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Corylus cornuta

INTRODUCTORY

  California hazelnut in early spring, Calaveras Big Trees State Park. © 2007 Dr. Mark S. Brunell.
AUTHORSHIP AND CITATION:
Fryer, Janet L. 2007. Corylus cornuta. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/shrub/corcor/all.html [].

FEIS ABBREVIATION:
CORCOR
CORCORC
CORCORO

NRCS PLANT CODE [273]:
COCO6
COCOC
COCOC2

COMMON NAMES:
California hazelnut
beaked hazelnut

TAXONOMY:
Corylus cornuta Marshall (Betulaceae) is the scientific name of this species [88,102,128,144,210,253]. There are 2 subspecies:

Corylus cornuta subsp. californica (A. DC.) E. Murray, California hazelnut [88,263]
Corylus cornuta subsp. cornuta, beaked hazelnut [88]

Within this review, Corylus cornuta refers to the species as a whole. Subspecies are referred to by the common names above.

Hybrids: California hazelnut and beaked hazelnut hybridize and introgress (review by [111]) where their ranges overlap in southern British Columbia and eastern Oregon (review by [111]),[34,126].

In the laboratory, California hazelnut was outcrossed as the female parent with 7 other hazelnut species [80]. Although California hazelnut does not naturally cooccur with other native hazelnut species, hybridization is possible in the Willamette Valley of Oregon and other locations where California hazelnut grows adjacent to European filbert (C. avellana) orchards [81].

Beaked hazelnut hybridizes naturally with American hazelnut (C. americana) [52] but apparently does not easily hybridize with other hazelnut species [80].

SYNONYMS:
California hazelnut—
Corylus cornuta var. californica (A. DC.) Sharp [128,144]
Corylus californica (A. DC.) Rose [144]

beaked hazelnut—
Corylus cornuta var. cornuta [126,130,144]
Corylus rostrata Ait. [144]

LIFE FORM:
Shrub-tree

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
The quaking aspen (Populus tremuloides)/beaked hazelnut forest alliance of North Dakota, South Dakota, Wyoming, and Colorado is ranked as G3 (imperiled globally because of rarity) by The Nature Conservancy [235]. Information on state-level protected status of Corylus cornuta in the United States is available at Plants Database.

DISTRIBUTION AND OCCURRENCE

SPECIES: Corylus cornuta
GENERAL DISTRIBUTION:
Corylus cornuta is native to southern Canada and the United States. It occurs from British Columbia east to Newfoundland and south to California, Colorado, Mississippi, and South Carolina [88,170]. Flora of North America provides a distributional map of Corylus cornuta and its subspecies.

California hazelnut is distributed contiguously from southwestern British Columbia south to south-central California, with a disjunct population in west-central British Columbia [88,170].

Beaked hazelnut occurs contiguously from north-central British Columbia east to Newfoundland and south to North Dakota, Iowa, Michigan, Alabama, and South Carolina. Disjunct populations occur in eastern Washington, northern Idaho and western Montana, northeastern Wyoming, west-central South Dakota, and north-central Colorado [88,171]. Beaked hazelnut is rare in Illinois and extirpated in Ohio [88].

HABITAT TYPES AND PLANT COMMUNITIES:
California hazelnut is a minor species, being "a rather unimportant constituent" in most plant communities in which it occurs [60]. It may be frequent to dominant on shrublands in postfire and other early disturbance succession, however. For example, a 1962 survey on the Tillamook Burn of northwestern Oregon showed that 17 years after the last of 3 repeat wildfires (1933, 1939, and 1945), California hazelnut frequency ranged from 66% to 83% in red alder (Alnus rubra)- and vine maple (Acer circinatum)-dominated associations [17]. California hazelnut is most common in coast Douglas-fir (Pseudotsuga menziesii var. menziesii)-hardwood mixed-evergreen forests. It is a component of mixed-conifer forests and hardwood woodlands. Vegetation classifications describing plant communities where California hazelnut is dominant are listed below.

California: Oregon: Beaked hazelnut is common to dominant in seral aspen (Populus spp.) and pine (Pinus spp.) communities of the Great Lakes states and the Northeast [156,218]. It is the most common understory dominant in aspen-birch (Betula spp.) forests of those regions. In the southern Canadian provinces and the Great Lakes States, beaked hazelnut forms an often dense understory beneath quaking aspen canopies [132,132]. Beaked hazelnut was the most important shrub, for example, in a quaking aspen-paper birch-red maple-sugar maple (Betula papyrifera-Acer rubrum-Acer saccharum) Wisconsin forest, comprising 60% to 70% of total understory shrub biomass [65]. Beaked hazelnut also frequently dominates the understories of jack pine (P. banksiana) and/or red pine (P. resinosa) forests and mixed conifer-hardwood forests [218,238]. A beaked hazelnut population study in Itasca State Park, Minnesota, found mean beaked hazelnut coverage was greater in quaking aspen-paper birch and jack pine and/or red pine forest types than in sugar maple-basswood (Tilia americana) or balsam fir-white spruce (Abies balsamea-Picea abies) forest types [156]. Beaked hazelnut sometimes codominates with American hazelnut, particularly in pine communities of the Great Lakes region [237,245].

Beaked hazelnut is a minor component of coastal grassland, little bluestem (Schizachyrium scoparium) prairie, and yellow sedge (Carex pensylvanica) meadows on Massachusetts's coastal islands [78]. It is noted on grass-sedge (Poaceae-Carex spp.) balds in the southern Appalachian Mountains [288] and in upland loblolly pine-oak (Pinus taeda-Quercus spp.) coves on the Coastal Plain of Alabama [23]. It is rare in Engelmann spruce-subalpine fir (Picea engelmannii-A. lasiocarpa) forests of eastern British Columbia [294].

Vegetation classifications describing plant communities where beaked hazelnut is dominant are listed below.

United States
Colorado:

Michigan: Minnesota: North Carolina: Wisconsin: West Virginia: Regions: Canada
Alberta: New Brunswick: Manitoba: Ontario: Quebec:

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Corylus cornuta
California hazelnut. Charles Webber © California Academy of Sciences.   Beaked hazelnut. Dave Powell, USDA Forest Service, Bugwood.org

GENERAL BOTANICAL CHARACTERISTICS:
This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (for example, [88,128,210]).

Corylus cornuta is a deciduous shrub or small tree with ascending branches. Leaves are thin to leathery, hairy, and have serrated edges. The inflorescences are catkins. Male and female catkins develop on separate twigs before leaf emergence (review by [246]). Male catkins grow laterally on short shoots of branchlets, usually in clusters of 2 to 3. Female catkins are small and ovoid in shape, and clustered at the ends of short branches. The fruit is a stiff, hairy involucre with a long, tubular beak shape. The seeds are unwinged nuts, growing in clusters of 2 to 6 [88,98,253,272]. Corylus cornuta's root and rhizome system is shallow (review by [246]).

California hazelnut is a 13- to 49-foot (4-15 m)-tall shrub or small tree. It typically has several trunks. Twigs are slender and may grow in a zigzag pattern. Male catkins measure 0.2 to 0.3 × 1.6 to 2.4 inches (0.5-0.8 × 4-6 cm). Nuts are in clusters of 2 to 4, with the involucral beak less than 2 times the length of the nuts [88,126,128]. California hazelnut is usually not rhizomatous (review by [111]).

Stand structure: California hazelnut varies in habit from scattered individual plants to densely clumped thickets [34]. Isolated shrubs are typical (review by [111]).

Beaked hazelnut is a 13- to 20-foot (4-6 m)-tall shrub [88]. Its typical growth form is densely clonal. Through much of its range, beaked hazelnut clones have multiple stems. On the Cloquet Forestry Center, stems grew at about 2-foot (0.6 m) spacing [34,178]. In the extreme western edge of its distribution, beaked hazelnut usually has several stems radiating from a single root crown [34]. Leaf size varies from 1 to 5 inches (3-10 cm) long and 0.8 to 3.0 inches (2.0-7.6 cm) wide [135]. Male catkins measure 0.2 to 0.3 × 1.8 to 2.4 inches (0.5-0.8 × 4.5-6 cm) [34,88]. Beaked hazelnut is predominantly monoecious, but ratios of male:female flowers may vary within and between populations. In northern Minnesota, male flowers were more numerous than female flowers, and male flowers were produced at a younger stem age. Some plants had only male or only female flowers while some had both flower types on separate branches, but the majority produced mostly male flowers with some female flowers on the same branches [135]. The involucral beak of beaked hazelnut's fruit is 2 to 4 times the length of the nut [34,88].

Beaked hazelnut has a shallow, dense, extensive underground system [166] that includes a taproot and intertwined lateral roots and rhizomes (reviews by [111,246]),[135]. Over 90% of beaked hazelnut roots and rhizomes are in the top 6 inches (20 cm) of soil (review by [246]),[135]. On undisturbed sites in Minnesota, Buckman [39] found the majority of beaked hazelnut rhizomes grew in the bottom of the organic soil layer, lying at or close to mineral soil. Beaked hazelnut's taproot generally extends 2+ feet (0.6 m) below the soil surface [135].

Stand structure: Beaked hazelnut's rhizomatous habit generally produces thickets that form a continuous understory in the absence of disturbance (review by [111]). Where beaked hazelnut is dominant, stem density may exceed 3,000 stems/acre in mature beaked hazelnut understories and 60,000 stems/acre in seral stands [68,258]. Light intensity beneath a beaked hazelnut thicket may be 2% to 7% of full sun (review by [246]). A study on the Riding Mountain Forest Experimental Station, Manitoba, showed that on a 1-acre (0.4 ha) plot, total leaf surface area of beaked hazelnut was approximately 7 acres (3 ha) (review by [281]). Hogg and others [132] provide leaf area index and photosynthesis measurements for beaked hazelnut and quaking aspen in a quaking aspen/beaked hazelnut forest in Prince Albert National Park, Saskatchewan. Reiners [214] provides a comprehensive stand structure analysis of a northern pin oak-red maple-paper birch/speckled alder (Alnus incana subsp. rugosa)-beaked hazelnut community in the Cedar Creek Natural History Area of Minnesota, including litter and woody debris biomass, productivity, and species diversity of the tree, shrub, and ground layers.

RAUNKIAER [212] LIFE FORM:
Phanerophyte
Geophyte

REGENERATION PROCESSES:
Corylus cornuta reproduces from seed and vegetatively. Vegetative reproduction is more common (reviews by [111,246]). Seed regeneration is important for Corylus cornuta establishment on new sites [68,258].

Pollination: Corylus cornuta is wind pollinated [126,135]. In a northern Minnesota field study, successful fertilization ranged from 54% to 81%, with the largest female catkins having highest rates of pollination [135].

Breeding system: Corylus cornuta is mostly monoecious, although some plants are dioecious [102,135,253]. Laboratory pollination studies showed self-incompatibility in beaked hazelnut; however, 25% of California hazelnut selfings produced viable nuts. Selfing is reportedly rare in Corylus spp., and the researchers recommended further breeding studies for California hazelnut to determine how common selfing may be in California hazelnut populations [81].

Seed production: Top-killed Corylus cornuta generally produce male catkins from new sprouts in the next flowering cycle [46]. On the Cloquet Forestry Center of northern Minnesota, male catkins were produced on 1-year-old beaked hazelnut sprouts, while female catkins grew on 2-year-old sprouts. Maximum production occurred when sprouts were around 11 years of age. Stems stopped producing nuts at around age 18. Saplings rarely flower; typically, plants are top-killed and sprout before first flowering [135]. Large nut crops are produced about every 2 to 3 years (review by [20]). In Alberta, beaked hazelnut nut production in a quaking aspen/beaked hazelnut stand varied temporally from approximately 13,000 nuts/acre in 1968 to 44 nuts/acre in 1969 (review by [246]). In a quaking aspen-balsam poplar stand near Edmonton, New York, beaked hazelnut production was estimated at 6,400 nuts/acre [148]. Heavily shaded Corylus cornuta stems may not flower or fruit (review by [246]),[35]. Rodents (review by [246]) and hazelnut weevils [269] can seriously depredate nut crops.

Seed dispersal: A variety of birds and mammals disperse the nuts. Jays and rodents are most important to successful Corylus cornuta seed dispersal and subsequent seedling establishment [20,93]. Steller's jays and scrub jays collect and cache California hazelnut seeds. They may disperse nuts over relatively long distances [35]. Blue jays are the primary avian dispersers and cachers of beaked hazelnut seeds [141]. Red squirrels and least chipmunks are important rodent cachers of beaked hazelnut seeds. Rodents typically disperse Corylus cornuta nuts 100 feet (90 m) or less. Seed predation rates are generally high, but animal seed caching is probably critical to Corylus cornuta seedling establishment. Most nuts above the litter layer are consumed; if not, they generally desiccate and die quickly. A study on the Cloquet Forestry Center showed red squirrels and least chipmunks scatter-hoarded beaked hazelnut nuts under leaves or in soil. More than 66% of scatter-hoarded nuts were consumed or relocated by the rodents [135]; however, remaining cached nuts were protected by litter and/or soil, so they had a better chance of germinating and establishing than uncached nuts. Gravity and water disperse some nuts [135,184], although gravity and water do not disperse nuts effectively on flat lands [258].

Seed banking: Hazelnut (Corylus spp.) seeds remain viable about 1 year. Given the short seed life and high predation rates of Corylus cornuta nuts [20], it is unlikely that Corylus cornuta retains a seed bank.

Germination: Corylus cornuta nuts are not dormant at ripening, but dry environmental or storage conditions induce chemical dormancy. Mechanical restriction imposed by the hard pericarp further inhibits germination. Overwinter (3- to 6-month) stratification breaks nut dormancy [20,53,135]. Germination is hypogeal [20]. Chan [53] obtained 40% to 88% germination of stratified California hazelnut nuts in the greenhouse. Other studies report 30% to 60% germination in the laboratory (review by [246]). Both germination and establishment rates are low in dense shade. Corylus cornuta nuts show low germination rates when not protected by litter and/or soil (review by [246]). In a laboratory experiment using seed from the Cloquet Forestry Center, germination of 1-year-old beaked hazelnut seeds was 0% for nuts stored room temperature, 34% for nuts in cold storage (20 °F (11 °C)), and 72% for nuts buried 1 foot (0.3 m) deep in mineral soil. In a related field experiment on the Cloquet Forestry Center using the same seed collection, mesic soil moisture conditions favored beaked hazelnut germination. Seeds hand-buried at a 1-foot depth showed 26% to 32% germination on upland jack pine communities and 0% germination in lowland swamps. Highest germination rates occurred in black spruce-tamarack (Larix laricina) stands, which grew between upland jack pine and lowland swamp communities [135].

Seedling establishment: Corylus cornuta seedling establishment is noted in most literature as sporadic and rare, occurring in years with high nut production and low rodent numbers (review by [246]). However, Corylus cornuta seedling establishment may be more frequent than previously thought on open sites that are not densely colonized by other plants [258]. Beaked hazelnut seedlings were noted as common in an open, seral white ash/grass-hawkweed (Fraxinus americana/Poaceae-Hieracium spp.) community in New Brunswick [221]. Seedling establishment was also documented in northern Minnesota. Study sites were on thinned red pine stands with sparse beaked hazelnut clumps in the understory. Beaked hazelnut plants on these study sites were young: 25% to 43% of clones were less than 20 years of age, and most were <12 inches (30 cm) in total clonal diameter [258]. Rhizome development begins at 7 to 12 years of age (review by [246]),[135,258], so rhizomes were relatively undeveloped in the young beaked hazelnut population [258], and there was still underground space available for seedlings to establish. Fire Case Studies provides a detailed account of beaked hazelnut establishment from both seed and rhizomes after prescribed burning in northern Minnesota.

Foraging by American beavers and other browsing mammals may reduce recruitment of Corylus cornuta seedlings and sprouts. In Ontario, beaked hazelnut abundance increased with distance from American beaver ponds [76].

Vegetative regeneration: Corylus cornuta sprouts from the root crown and/or rhizomes after top-kill. It may also layer [35,135],(reviews by [111,246]). Fire, heavy browsing, or mechanical damage promote sprouting (review by [246]),[51,135,293]. Saplings have few rhizomes; therefore, their ability to sprout is limited [68]

California hazelnut sprouts from the root crown [35,126]. Some eastern most populations may sprout from rhizomes [35].

Beaked hazelnut sprouts from rhizomes and/or the root crown [162,258] and sometimes regenerates by layering [46]. A combination of rhizome and root crown sprouting is most common [34,46,210,260] except in the extreme western portion of beaked hazelnut's range, where beaked hazelnut may be only weakly rhizomatous or lack rhizomes [34]. Mature beaked hazelnut populations in the Great Lakes states and the Northwest have extensive rhizome and root systems that support prolific sprouting and development of dense thickets [162,258].

Growth: Clonal development and growth are slow for young Corylus cornuta plants (review by [246]). Hsiung [135] details embryonic, seedling, sapling, and clonal growth stages of a beaked hazelnut population on the Cloquet Forestry Center. He found that beaked hazelnut plants have 3 developmental stages: a 10- to 15-inch-tall (25-38 cm) seedling stage until ages 7 to 12; a period of rhizome and aerial shoot development until around age 40; and maturation into large shrubs after about age 40. Even at age 20, clones remained relatively small (10-12 inches (25-30 cm) in diameter). Six-year-old clones had a mean total crown diameter of 0.8 inch (2 cm) and supported 2 to 3 spouts, while 38-year-old clones averaged 7.9 feet (2.4 m) in total crown diameter, with an average of 25 stems [135].

Sprout growth is greatly accelerated in mature clones compared to aerial stem growth of seedlings and saplings [135]. Mature Corylus cornuta plants top-killed by fire or other disturbance generally reach 2 feet (0.6 m) in height after 2 growing seasons and 8 feet (2 m) after 15 to 20 years. "Decadent" stems may grow only 1 inch (2.5 cm)/year (review by [246]). Beaked hazelnut sprouted from rhizomes after glyphosate treatments on a jack pine plantation in Ontario. Before spraying, beaked hazelnut plants had mean crown and root crown diameters of 4.4 feet and 1.3 inches (1.4 m and 3.2 cm), respectively. Two years after spraying, distance between beaked hazelnut sprouts averaged 19.3 inches (49 cm). There was a mean of 8 shoots/node, and shoots averaged 3.2 feet (1.0 m) in height. Crowns and root crown diameters were not remeasured [178].

Plant communities with open structure support rapid Corylus cornuta growth. A beaked hazelnut population study in undisturbed, open quaking aspen and jack pine-red pine forests in Itasca State Park showed continual recruitment of beaked hazelnut stem sprouts over 19 years of study. Stem recruitment was less during drought years, but overall stem recruitment (x=32 stems/ha) was steady across the 19 study years. Beaked hazelnut stem density in sugar maple-basswood and balsam fir-white spruce forests, which were less open, declined 61% during the study period (x=4.5 stems/ha) [156].

Mortality: In an age class study of beaked hazelnut in a quaking aspen forest in northern Minnesota, beaked hazelnut showed a constant mortality rate across quaking aspen stand age (0-100 years). High light intensity favored beaked hazelnut regeneration, while dense basal area of overstory trees increased beaked hazelnut mortality [157].

Underground Corylus cornuta clone age may be great, but individual aerial stems are short lived. On the Cloquet Experimental Forest, maximum aboveground stem age was 21 years. Most stems did not flower past age 18 [135].

SITE CHARACTERISTICS:
California hazelnut—
This subspecies is most common on mesic and/or lightly shaded sites [128]. It is grows on wooded hillsides and streambanks and in coves and canyons [70,88]. In the Willamette Valley, California hazelnut occurs on well-drained hillsides, old fields, logged sites, and burns [33]. California hazelnut is not as well adapted to cold sites as beaked hazelnut [246]. In British Columbia, where California hazelnut is at the edge of its northern range, it occurs only on sheltered sites in the rain shadow of the Coast Ranges (review by [111]).

Soils: California hazelnut grows on well-drained soils [70,268,272]. Soil textures supporting California hazelnut include sands, sandy loams, and gravels [70,272]. California hazelnut does not grow well in clays (review by [111]),[150], and cannot tolerate poorly drained [130] or serpentine soils [123]. California hazelnut is an indicator species for low-elevation, warm sites with well-drained soils in western Oregon and southwestern Washington [116].

California hazelnut prefers moist soils and may not grow in dry soils in the southern portion of its range. In giant sequoia (Sequoia gigantea) groves and white fir (Abies concolor) forests of Sequoia-Kings Canyon National Park, California, California hazelnut is restricted to sites with high soil moisture in summer months [229,230]. California hazelnut is noted on some sites that dry out in summer, however. It grows on rocky slops in the Coast Ranges [88]. On the western slopes of the Cascade Range of Oregon, Douglas-fir/California hazelnut-salal (Gaultheria shallon) communities occur mostly on ridgetops and upper south-facing slopes, while Douglas-fir /vine maple-Pacific rhododendron (Acer circinatum-Rhododendron macrophyllum) communities occur on more mesic topographic positions [115].

Elevation: California hazelnut is found from 3,300 to 8,200 feet (1,000-2,500 m) across its range [88]. It occurs below 6,900 feet (2,100 m) in California [128] and from 0 to 2,600 feet (800 m) in western British Columbia (review by [111]).

Beaked hazelnut—
This subspecies generally grows on moist to dry roadsides, "waste places", fencerows, pastures, thickets, wood edges, and in the understory of open woodlands and forests [88,98,102,246]. It grows on dry, rocky soils in the piedmont and mountainous areas of the Carolinas [210]. Soil texture, soil moisture content, and light intensity are apparently critical factors in determining where beaked hazelnut can grow [135].

Soils: Beaked hazelnut distribution is irregular across the landscape, with beaked hazelnut growing only on sites with suitable soil textures and moisture content. Beaked hazelnut gains greatest biomass in loamy soils, especially loamy sands [135]. Moisture regime is wet-mesic to dry-mesic, with dry-mesic soils preferred [62,227,291]. In the northern United States, beaked hazelnut generally grows on mesic sites while American hazel grows on xeric sites, although there are many exceptions [39]. Rowe [227] lists beaked hazelnut as an indicator species of xero-mesic soils on Duck Mountain Forest Reserve, Saskatchewan. Beaked hazelnut does not grow well on fine-textured clays and wet soils such as mucks and peats [135,181]. It is anecdotally reported as flood intolerant [36]. Soils supporting beaked hazelnut are generally moderately to highly rich in nutrients (review by [111]) and range from strongly to slightly acid (pH 5.3-6.1) (review by [246]),[135]. On the Cloquet Forestry Center, beaked hazelnut was most frequent on sites with a soil moisture content of 20% and did not occur on sites with soil moisture contents >56%. Mineral soils or soils with low organic content were favored. Beaked hazelnut coverage was greatest on soils with 10% organic matter content, and beaked hazelnut did not occur on sites where soil organic matter content was >53%. Optimum pH range was from 5.7 to 6.3 [135]. Across the Canadian provinces, beaked hazelnut is an indicator species of basic, calcium-rich soils with high levels of available nitrogen and a fresh (dry-mesic) soil moisture regime. In British Columbia, beaked hazelnut frequency decreases with increasing precipitation and latitude and increases with increasing continentinality of climate [218].

Elevation: Beaked hazelnut occurs from 300 to 2,000 feet (100-500 m) across its geographical range [88]. It ranges from 100 to 2,800 feet (30-850 m) in the Adirondack Mountains [154] and from 2,000 to 3,000 feet (500-1,000 m) in Alberta [62].

SUCCESSIONAL STATUS:
Corylus cornuta is most common in early forest succession but may persist into late succession (review by [246]),[74,245]. It is moderately shade tolerant [147,176]. Overstory removal by fire, logging, or other means usually increases Corylus cornuta density and height [58,61,213]. Corylus cornuta maybe slow to establish on sites where it was not previously present. Seedling establishment is rarely observed in closed, late-seral communities [58] but may occur on open, sparsely vegetated sites. Beaked hazelnut seedlings were noted, for example, on coal mine spoils in Alberta [231] and in young red pine-jack pine stands on the Cloquet Forestry Center [68]. See Fire Case Studies for a detailed report on beaked hazelnut seedling establishment after prescribed fire on the Cloquet Forestry Center. For further details on beaked hazelnut and California hazelnut establishment after fire, see Plant Response to Fire.

California hazelnut occurs in both early and late succession. It occurs, for example, in logged, slash-burned, and old-growth Douglas-fir forests on the Coast Ranges [18,113] and in mid- to late-seral black cottonwood (Populus balsamifera subsp. trichocarpa) communities by the Willamette River, Oregon [85]. Logging generally favors California hazelnut. In a Douglas-fir forest on the Willamette National Forest, California hazelnut was positively correlated (r>0.50) with thinning treatments [25]. In the Columbia River Gorge of Oregon and Washington and on the foothills above Willamette Valley, California hazelnut-vine maple-cascara (Rhamnus purshiana) shrub communities form on powerline rights-of-way. Periodic removal of trees arrests the shrublands in early succession [236]. Whittaker [290] described California hazelnut as a late-successional invader on mountain meadows in the Siskiyou Mountains of Oregon.

California hazelnut may persist into late succession, although it is more common in seral communities. In the Willamette Valley, California hazelnut grows in late-successional Oregon white oak/California hazelnut-poison-oak-Saskatoon serviceberry (Toxicodendron diversilobum-Amelanchier alnifolia) communities where fire has been excluded for 140+ years [33,265]. California hazelnut may be important in gap succession in mature and old-growth Douglas-fir forests. On foothills above Willamette Valley, California hazelnut was significantly more frequent (P=0.1) in small forest openings compared to closed forest [232].

Beaked hazelnut: Many studies document beaked hazelnut's dominance or strong presence in early seral communities. Most disturbances that open the canopy—including fire, insects, disease, and logging—increase beaked hazelnut frequency [281]. For example, a study of succession following a spruce budworm outbreak in northern Minnesota found beaked hazelnut was a strong "invader" after death of the balsam spruce and white spruce overstory [22], although it is likely that dense beaked hazelnut establishment was from preexisting rhizomes, not from seed. Beaked hazelnut and other shrubs were densest where overstory mortality exceeded 80%. Beaked hazelnut density averaged 15,340 stems/ha 23 years after the spruce budworm infestation [22]. In eastern Quebec, beaked hazelnut was more common in a 20-year-old balsam fir-yellow birch clearcut than in a mature adjacent balsam fir-yellow birch forest, with densities of 300 and 25 beaked hazelnut stems/acre in seral and mature stands, respectively [14]. Analyses of disturbed sites in Manitoba revealed that beaked hazelnut was the most abundant shrub on burned, logged, or spruce budworm-attacked sites, with mean coverages (frequencies in parentheses) of 21.2% (6%), 48.6% (19%), and 14.7% (21%), respectively. As an indicator species of fire, logging, or spruce budworm disturbance, beaked hazelnut was ranked third highest of 52 understory species (indicator-species value=61.2, P≤0.01) [147].

Logging: Recovery of preharvest beaked hazelnut cover on logged sites is generally rapid [5]. A successional study on the Superior National Forest, Minnesota, found beaked hazelnut was more common on logged, logged and slash-burned, and logged and rock-raked sites than on unlogged jack pine-black spruce forest [191]. Successional data spanning 50+ years are available for a logged sugar maple-yellow birch forest on the Upper Peninsula Experimental Forest of Michigan. Beaked hazelnut declined with time-since-logging. The study site was inventoried in 1926; clearcut in 1927; and partially cut in 1929, 1944, 1955, and 1966. A severe windstorm in 1953 caused blowdowns; otherwise, the site was not subject to stand-replacement events other than logging after 1926. Vegetation was reinventoried in 1931 and 1977. Beaked hazelnut was an important understory shrub in the 1926 and 1931 inventories (importance value=2), but in the 1977 inventory it was represented only as scattered large individuals in the overstory (importance value=0) [186]. Beaked hazelnut can be slow to establish after logging where it was not present before tree harvest [46].

Beaked hazelnut declines with canopy closure [138,156,245,246,252,287], while disturbances that open the canopy favor beaked hazelnut. On the Stephens State Forest of Iowa, beaked hazelnut was not reported in closed-canopy mixed-oak forest but was a dominant shrub in open mixed-oak forest-prairie transition communities [66]. Beaked hazelnut is most prevalent where ≥30% of full sunlight is available: Dense thickets usually form when beaked hazelnut grows in the open (reviews by [103,246]),[135]. Beaked hazelnut is common in early stages of succession from old fields to mixed pine-hardwood forest (review by [246]). It may be "weedy" in highly managed forests in the Great Lakes states [88].

Beaked hazelnut may persist into late forest succession when enough light reaches the beaked hazelnut subcanopy for maintenance [246], and may dominate on late-successional sites that cannot support trees. Beaked hazelnut persisted from early to late postfire succession in balsam fir-basswood forests of Itasca County, New York [101]. It was a component of a remnant old-growth white pine-eastern hemlock forest in New Hampshire [19] and occurred in mature, old-growth, and senescent balsam fir forests of the Gaspé Peninsula, Quebec [74]. It is important in old-growth gap succession [91] and may increase when the overstory senesces [281]. In Itasca State Park and Duck Mountain Provincial Park, Manitoba, beaked hazelnut increased with overstory decline in decadent quaking aspen stands [89,120]. Beaked hazelnut was noted as a late-successional species in rock outcrop succession in Manitoba, cooccurring with chokecherry and other shrubs species that established after pioneering lichens and grasses contributed organic matter and litter to the soil seedbed [90]. Beaked hazelnut is infrequent in closed-canopy, old-growth forests [87].

SEASONAL DEVELOPMENT:
California hazelnut—
California hazelnut catkins bud out before leaves elongate in spring [34]. Nuts develop in late summer [20] and ripen in late summer to early fall. The nut sheath turns brown at ripening [53]. Ripe California hazelnut seeds may remain on the tree longer than beaked hazelnut seeds [53]. California hazelnut seeds are sometimes winter-persistent [126].

California hazelnut phenology
Area Flowers Fruits
California Jan.-March [20,272] Sept.-Oct. [20]
Oregon early March [111] published data not available as of 2007
     Willamette, Mt Hood, & Siuslaw
     National Forests		 Jan.-March [268] published data not available as of 2007
west coast states and British Columbia very early spring [70,88] Sept.-Nov. [70]
British Columbia published data not available as of 2007 Aug.-Sept.

Beaked hazelnut—
Beaked hazelnut flowers in very early spring across its range [88,98,210]. Catkins grow first, expanding 5 to 15 days before leaves [135]. After rapid spring elongation, staminate catkins grow slowly through midsummer [98,135,210]. April pollen release is reported for beaked hazelnut in the Adirondack Mountains of New York [154] and northern Minnesota. Leaves expand from late April to late May in northern Minnesota, and vegetative growth stops in late July [135]. Nuts develop in late summer [20] and abscise when fully ripe in fall [53,135]. Growth ceases around September (reviews by [135,246]). Most leaves have fallen by late September in northern Minnesota [135].

Beaked hazelnut phenology
Area Flowers Fruits
Carolinas Feb.-March Sept. [210]
Great Plains Apr.-May [102] Sept. [102]
Tennessee Jan.-Feb. Aug.-Sept. [20]
Minnesota April-May Aug.-Sept (review by [246]),[135]
West Virginia April-May [253] published data not available as of 2007
north-central Wisconsin published data not available as of 2007 late July [54]

FIRE ECOLOGY

SPECIES: Corylus cornuta
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Corylus cornuta sprouts from the root crown after top-kill by fire. Some populations also sprout from rhizomes after top-kill. Ability to develop rhizomes is strongest in Corylus cornuta populations in the Great Lakes states and Northeast, with rhizomatous habit apparently lessening towards the species' western distribution.

As of 2007, only a few studies documented postfire seedling establishment in Corylus cornuta [68,153,256]. Corylus cornuta seedling establishment is probably minor in populations that had well-developed rhizomes before top-kill [153]. Strong spatial dominance of Corylus cornuta rhizomes and roots apparently competitively excludes Corylus cornuta seedlings (reviews by [111,246]). Seedling establishment may be more important where stand structure of mature beaked hazelnut clones is patchy, for rhizomatous populations that are young and have not yet developed rhizomes, and for nonrhizomatous populations. Regeneration from seed provides opportunity for Corylus cornuta colonization on burns and other disturbed sites [68,258]. Since Corylus cornuta is adapted for seed dispersal by animals [20,93], it is likely that postfire seed dispersal and seedling establishment is important for population expansion and maintenance of genetic diversity.

California hazelnut sprouts from the root crown after top-kill by fire [35,126]. Some easternmost populations may sprout from rhizomes [35], although their ability to do so after fire had not been studied as of 2007.

Beaked hazelnut sprouts from the root crown after top-kill by fire. Populations in the Great Lakes states and the Northeast also sprout from rhizomes [6,95,147,153,158,215,246,272]. With a few exceptions [207,254], studies on beaked hazelnut response to fire found in this literature review were conducted in the Great Lakes states or northeastern portions of Canada and the United States, where beaked hazelnut is strongly rhizomatous. Beaked hazelnut populations elsewhere may not achieve as great a coverage after fire compared to northern populations.

Beaked hazelnut is often a minor to rare plant outside the Great Lakes and northeastern regions [235,273], and strength of rhizomatous habit is not well documented for populations outside those regions. Since beaked hazelnut apparently does not form extensive thickets towards its western distribution, it is possible that some western populations sprout mostly from root crowns. Understanding interpopulational differences in beaked hazelnut's ability to sprout after fire is important in predicting beaked hazelnut's ability to establish after fire. Fire ecology studies on beaked hazelnut populations in the Appalachians, Midwest, and Great Plains are needed to understand the breadth of postfire and other postdisturbance responses in beaked hazelnut.

Fire regimes:
California hazelnut
Beaked hazelnut

California hazelnut— Forests and woodlands with California hazelnut historically experienced short return-interval surface fires and/or mixed-severity fires [145,261]. Fire altered woodland and forest structure by reducing density of California hazelnut and other shrubs and late-successional, fire-sensitive conifers. Large, fire-resistant trees were generally retained [30,278,279].

Native Americans increased fire frequency in coniferous forests with a California hazelnut component by setting fires. Processing California hazelnut seeds and increasing density of California hazelnut sprouts were objectives of such fire use [159,168,270]. Low-severity summer or fall surface fires roasted fallen nuts and burned off the nut shells [159]. The nuts were collected for food after the fire had passed, and next-year sprouts were used in basketry [12,13,33,169,215]. The Coquille of Oregon burned California hazelnut fields about every 5 years to promote sprout and nut production [159].

Conifer forests: Coast Douglas-fir communities, where California hazelnut is most common, had mixed-severity fires ranging from less than 3-year to longer than 50-year intervals. Mean fire-return intervals have become longer since fire exclusion began in the 1900s. A fire history study of Douglas-fir-sugar pine/tanoak-Pacific madrone/California hazelnut-Oregon grape (Mahonia nervosa) forest on the Klamath and Six Rivers National Forests of California revealed fire-return intervals ranging from 5 to 41 years in the presettlement period, 7 to 26 years in the settlement period, and 3 to 71 years in the fire exclusion period. Mean fire-return intervals for those periods were 13.8, 13.4, and 37.4 years, respectively [292]. California hazelnut coverage declines in coast Douglas-fir forests as time-since-disturbance increases [25].

Fire-return intervals in ponderosa pine and ponderosa pine-California black oak forests historically increased with increasing elevation in the Sierra Nevada [48], with a tendency towards shorter mean fire-return intervals (5-15 years) on dry, west- and south-facing slopes and longer fire-return intervals (15-25 years) on mesic, east- and north-facing slopes. Midelevation forests typically had mixed-severity fires that created patchy mosaics [86]. Fire-return intervals for ponderosa pine forests ranged from 6 to 22 years in the Cascade Range of southern Oregon and northern California (review by [217]).

At higher elevations, Sierra Nevada mixed-conifer forests had historically longer fire-return intervals compared to lower-elevation ponderosa pine forests. The fire regime was mostly low-severity underburns at intervals ranging from 7 to 16 years [279]. Studies on the Feather River-San Joaquin River watershed of the Sierra Nevada show a historic fire-return interval ranging from 7 to 9 years in the mixed-conifer zone [275]. A Lake Tahoe study showed a range from 5 to 15 years from 1649 to 1921 [248]. In giant sequoia groves, where California hazelnut is a common understory associate, understory fires historically reoccurred at 2- to 39-year intervals [48,149].

Forests in the northern portion of California hazelnut's range historically had longer fire-return intervals than forests to the south. Agee and others [4] report an historic 93-year mean fire-return interval for Douglas-fir-grand fir forests in the Desolation Peak area of the Cascade Range in Washington. The type, which has an understory component of California hazelnut, is a transition type between western hemlock-Pacific silver fir (Abies amabilis) forests of the coast and ponderosa pine forests of the interior Cascade Range [4].

Western hardwood communities such as Oregon white oak (Quercus garryana) and blue oak historically experienced frequent surface fires at intervals of <10 years [2,3,163,242].

The following table provides fire regime information that may be relevant to California hazelnut.

Fire regime information on vegetation communities in which California hazelnut may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [161]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the PDF file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Pacific Northwest
California
Pacific Northwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Northwest Woodland
Oregon white oak-ponderosa pine Replacement 16% 125 100 300
Mixed 2% 900 50  
Surface or low 81% 25 5 30
Pine savannah (ultramafic) Replacement 7% 200 100 300
Surface or low 93% 15 10 20
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Oregon white oak Replacement 3% 275    
Mixed 19% 50    
Surface or low 78% 12.5    
Northwest Forested
Douglas-fir (Willamette Valley foothills) Replacement 18% 150 100 400
Mixed 29% 90 40 150
Surface or low 53% 50 20 80
Oregon coastal tanoak Replacement 10% 250    
Mixed 90% 28 15 40
Ponderosa pine (xeric) Replacement 37% 130    
Mixed 48% 100    
Surface or low 16% 300    
Dry ponderosa pine (mesic) Replacement 5% 125    
Mixed 13% 50    
Surface or low 82% 8    
Douglas-fir-western hemlock (dry mesic) Replacement 25% 300 250 500
Mixed 75% 100 50 150
Douglas-fir-western hemlock (wet mesic) Replacement 71% 400    
Mixed 29% >1,000    
Mixed conifer (southwestern Oregon) Replacement 4% 400    
Mixed 29% 50    
Surface or low 67% 22    
California mixed evergreen (northern California) Replacement 6% 150 100 200
Mixed 29% 33 15 50
Surface or low 64% 15 5 30
Mixed conifer (eastside dry) Replacement 14% 115 70 200
Mixed 21% 75 70 175
Surface or low 64% 25 20 25
Mixed conifer (eastside mesic) Replacement 35% 200    
Mixed 47% 150    
Surface or low 18% 400    
Red fir Replacement 20% 400 150 400
Mixed 80% 100 80 130
Spruce-fir Replacement 84% 135 80 270
Mixed 16% 700 285 >1,000
California
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
California Shrubland
Chaparral Replacement 100% 50 30 125
Montane chaparral Replacement 34% 95    
Mixed 66% 50    
California Woodland
California oak woodlands Replacement 8% 120    
Mixed 2% 500    
Surface or low 91% 10    
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
California Forested
California mixed evergreen Replacement 10% 140 65 700
Mixed 58% 25 10 33
Surface or low 32% 45 7  
Coast redwood Replacement 2% ≥1,000    
Surface or low 98% 20    
Mixed conifer (North Slopes) Replacement 5% 250    
Mixed 7% 200    
Surface or low 88% 15 10 40
Mixed conifer (South Slopes) Replacement 4% 200    
Mixed 16% 50    
Surface or low 80% 10    
Aspen with conifer Replacement 24% 155 50 300
Mixed 15% 240    
Surface or low 61% 60    
Jeffrey pine Replacement 9% 250    
Mixed 17% 130    
Surface or low 74% 30    
Interior white fir (northeastern California) Replacement 47% 145    
Mixed 32% 210    
Surface or low 21% 325    
Red fir-white fir Replacement 13% 200 125 500
Mixed 36% 70    
Surface or low 51% 50 15 50
Red fir-western white pine Replacement 16% 250    
Mixed 65% 60 25 80
Surface or low 19% 200    
*Fire Severities:
Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Surface or low=Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects [117,160].

Beaked hazelnut is a moderately shade tolerant, seral subspecies, so it is most common in plant communities with frequent to moderate-length fire-return intervals. Aspen, pine, and mixed hardwood-pine forests, where beaked hazelnut is most common, historically had short fire-return intervals. A fire history of a red pine-eastern white pine forest in Pictured Rocks National Lakeshore, Michigan, for example, revealed a mean fire occurrence rate of 1 wildfire/21.8 years prior to the 19th century. Beaked hazelnut was the second most common shrub on sites showing evidence of past fires [172]. A 30-year mean fire-return interval is reported for presettlement white spruce-quaking aspen/beaked hazelnut forests of Prince Albert National Park, Alberta (Weir, J., personal communication in [131]).

Fire history data show mixed hardwood-conifer forests of southern Ontario had fire-return intervals of about 70 years from 1696 to 1920. Fire exclusion has been practiced since then, and the fire-return interval is estimated at 936 years. Within Algonquin Provincial Park, Ontario, beaked hazelnut occurred primarily in the understories of forests that historically experienced frequent fire. Forests where beaked hazelnut was important were dominated by shade-intolerant species including aspen (Populus tremuloides and P. grandidentata), paper birch, eastern white pine, red pine, jack pine, and red oak. Fire-return intervals for the forests were 22 to 88 years for red pine-jack pine and eastern white pine stands and 70 to 240 years for stands of shade-intolerant hardwoods such as aspen, paper birch, and red oak [208].

On the Cloquet Forestry Center, beaked hazelnut was most frequent in jack pine (23%) and aspen-birch (21%) communities, which have short fire-return intervals, and least common in white spruce-balsam fir (6%) and lowland mixed-hardwood forest (6%) communities, which have longer fire-return intervals [135].

It is likely that infrequent, severe fires in aspen and pine ecosystems of the Northeast historically killed both the overstory and the beaked hazelnut understory. On severely burned pine sites, beaked hazelnut may have established along with the conifer seedlings that would eventually dominate the overstory [258]. In Minnesota, for example, annual rings of beaked hazelnut rhizomes were the same age as the jack pine overstory, suggesting that both beaked hazelnut and jack pine established from seed after a severe wildfire. Canopy closure when the jack pines were about 15 years old prevented further beaked hazelnut seedling establishment [37].

Beaked hazelnut occurrence is declining in some areas outside the Great Lakes, the Northeast, and northeastern Canada [88]. Excluding these northern regions, fire studies mentioning beaked hazelnut were few as of 2007. For other regions, plant communities where beaked hazelnut is a known component of the vegetation tend to have an open structure that was historically maintained by frequent fire or flooding. For example, beaked hazelnut occurs in interior ponderosa pine communities in the Black Hills, which historically experienced frequent surface fires approximately every 10 years [274], and in bur oak (Q. macrocarpa) communities of the Midwest, which also historically experienced surface fire about every 10 years [280]. In the Great Plains, moderate return-interval fires may have helped maintain beaked hazelnut occurrence in wooded draws and ravines within plains grassland and prairie communities, which had shorter fire-return intervals than the woody communities [241]. Studies are needed on the importance of fire in retaining beaked hazelnut as a component of the vegetation in plant communities where it is not dominant.

The following table provides fire regime information that may be relevant to beaked hazelnut. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".

Fire regime information on vegetation communities in which beaked hazelnut may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [161]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the PDF file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Pacific Northwest Northern Rockies Northern Great Plains Great Lakes Northeast
Southern Appalachians Southeast      
Pacific Northwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Northwest Woodland
Pine savannah (ultramafic) Replacement 7% 200 100 300
Surface or low 93% 15 10 20
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Northwest Forested
Ponderosa pine (xeric) Replacement 37% 130    
Mixed 48% 100    
Surface or low 16% 300    
Dry ponderosa pine (mesic) Replacement 5% 125    
Mixed 13% 50    
Surface or low 82% 8    
Northern Rockies
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Northern Rockies Shrubland
Riparian (Wyoming)
Mixed 100% 100 25 500
Mountain shrub, nonsagebrush Replacement 80% 100 20 150
Mixed 20% 400    
Northern Rockies Forested
Ponderosa pine (Northern Great Plains) Replacement 5% 300    
Mixed 20% 75    
Surface or low 75% 20 10 40
Ponderosa pine (Northern and Central Rockies) Replacement 4% 300 100 >1,000
Mixed 19% 60 50 200
Surface or low 77% 15 3 30
Ponderosa pine (Black Hills, low elevation) Replacement 7% 300 200 400
Mixed 21% 100 50 400
Surface or low 71% 30 5 50
Ponderosa pine (Black Hills, high elevation) Replacement 12% 300    
Mixed 18% 200    
Surface or low 71% 50    
Ponderosa pine-Douglas-fir Replacement 10% 250   >1,000
Mixed 51% 50 50 130
Surface or low 39% 65 15  
Douglas-fir (xeric interior) Replacement 12% 165 100 300
Mixed 19% 100 30 100
Surface or low 69% 28 15 40
Douglas-fir (warm mesic interior) Replacement 28% 170 80 400
Mixed 72% 65 50 250
Northern Great Plains
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Northern Plains Woodland
Oak woodland Replacement 2% 450    
Surface or low 98% 7.5
Northern Great Plains wooded draws and ravines Replacement 38% 45 30 100
Mixed 18% 94    
Surface or low 43% 40 10  
Great Plains floodplain Replacement 100% 500    
Great Lakes
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Great Lakes Woodland
Great Lakes pine barrens Replacement 8% 41 10 80
Mixed 9% 36 10 80
Surface or low 83% 4 1 20
Jack pine-open lands (frequent fire-return interval) Replacement 83% 26 10 100
Mixed 17% 125 10 100
Northern oak savanna Replacement 4% 110 50 500
Mixed 9% 50 15 150
Surface or low 87% 5 1 20
Great Lakes Forested
Northern hardwood maple-beech-eastern hemlock Replacement 60% >1,000    
Mixed 40% >1,000    
Conifer lowland (embedded in fire-prone system) Replacement 45% 120 90 220
Mixed 55% 100    
Conifer lowland (embedded in fire-resistant ecosystem) Replacement 36% 540 220 >1,000
Mixed 64% 300    
Great Lakes floodplain forest
Mixed 7% 833    
Surface or low 93% 61    
Great Lakes spruce-fir Replacement 100% 85 50 200
Minnesota spruce-fir (adjacent to Lake Superior and Drift and Lake Plain) Replacement 21% 300    
Surface or low 79% 80    
Great Lakes pine forest, jack pine Replacement 67% 50    
Mixed 23% 143    
Surface or low 10% 333
Maple-basswood Replacement 33% >1,000    
Surface or low 67% 500    
Maple-basswood mesic hardwood forest (Great Lakes) Replacement 100% >1,000 >1,000 >1,000
Maple-basswood-oak-aspen Replacement 4% 769    
Mixed 7% 476    
Surface or low 89% 35    
Northern hardwood-eastern hemlock forest (Great Lakes) Replacement 99% >1,000    
Oak-hickory Replacement 13% 66 1  
Mixed 11% 77 5  
Surface or low 76% 11 2 25
Pine-oak Replacement 19% 357    
Surface or low 81% 85    
Red pine-white pine (frequent fire) Replacement 38% 56    
Mixed 36% 60    
Surface or low 26% 84    
Red pine-white pine (less frequent fire) Replacement 30% 166    
Mixed 47% 105    
Surface or low 23% 220    
Great Lakes pine forest, eastern white pine-eastern hemlock (frequent fire) Replacement 52% 260    
Mixed 12% >1,000    
Surface or low 35% 385    
Eastern white pine-eastern hemlock Replacement 54% 370    
Mixed 12% >1,000    
Surface or low 34% 588    
Northeast
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Northeast Woodland
Eastern woodland mosaic Replacement 2% 200 100 300
Mixed 9% 40 20 60
Surface or low 89% 4 1 7
Rocky outcrop pine (Northeast) Replacement 16% 128    
Mixed 32% 65    
Surface or low 52% 40    
Pine barrens Replacement 10% 78    
Mixed 25% 32    
Surface or low 65% 12    
Oak-pine (eastern dry-xeric) Replacement 4% 185    
Mixed 7% 110    
Surface or low 90% 8    
Northeast Forested
Northern hardwoods (Northeast) Replacement 39% >1,000    
Mixed 61% 650    
Eastern white pine-northern hardwoods Replacement 72% 475    
Surface or low 28% >1,000    
Northern hardwoods-eastern hemlock Replacement 50% >1,000    
Surface or low 50% >1,000    
Northern hardwoods-spruce Replacement 100% >1,000 400 >1,000
Appalachian oak forest (dry-mesic) Replacement 2% 625 500 >1,000
Mixed 6% 250 200 500
Surface or low 92% 15 7 26
Beech-maple Replacement 100% >1,000    
Northeast spruce-fir forest Replacement 100% 265 150 300
Southeastern red spruce-Fraser fir Replacement 100% 500 300 >1,000
Southern Appalachians
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Southern Appalachians Woodland
Oak-ash woodland Replacement 23% 119    
Mixed 28% 95    
Surface or low 49% 55    
Southern Appalachians Forested
Bottomland hardwood forest Replacement 25% 435 200 >1,000
Mixed 24% 455 150 500
Surface or low 51% 210 50 250
Mixed mesophytic hardwood Replacement 11% 665    
Mixed 10% 715    
Surface or low 79% 90    
Appalachian oak-hickory-pine Replacement 3% 180 30 500
Mixed 8% 65 15 150
Surface or low 89% 6 3 10
Eastern hemlock-eastern white pine-hardwood Replacement 17% >1,000 500 >1,000
Surface or low 83% 210 100 >1,000
Oak (eastern dry-xeric) Replacement 6% 128 50  
Mixed 16% 50 20  
Surface or low 78% 10 1 10
Appalachian oak forest (dry-mesic) Replacement 6% 220    
Mixed 15% 90    
Surface or low 79% 17    
Southern Appalachian high-elevation forest Replacement 59% 525    
Mixed 41% 770    
Southeast
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Southeast Woodland
Pine rocklands
Mixed 1% 330    
Surface or low 99% 3 1 5
Southeast Forested
Mesic-dry flatwoods Replacement 3% 65 5 150
Surface or low 97% 2 1 8
Coastal Plain pine-oak-hickory Replacement 4% 200    
Mixed 7% 100      
Surface or low 89% 8    
*Fire Severities:
Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low=Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [117,160].

Fuels:
California hazelnut was rated low in relative flammability based on an assessment of scorch damage and fire consumption of shrub crowns. Aerial surveys were taken 8 months after the Hayfork Wildfire Complex on the Shasta-Trinity National Forest in California [286]. Rickard [216] provides seasonal (fall-summer) biomass measurements of 5 categories of litterfall from a Douglas-fir/California hazelnut-ocecanspray-redflower currant (Holodiscus discolor-Ribes sanguineum) forest near the Columbia River in Prescott County, Oregon.

Beaked hazelnut: Huang and Schoenau [136] measured rate of litter decay in a quaking aspen/beaked hazelnut forest in Prince Albert National Park. They provide equations for predicting litter decay rate in similar ecosystems. A northern Minnesota study found that beaked hazelnut litter in a red pine-paper birch/beaked hazelnut forest decayed rapidly relative to red pine and paper birch litter [257].

Leaf area overstory/understory indices are available for a quaking aspen-balsam poplar (Populus balsamifera subsp. balsamifera)/beaked hazelnut forest in Prince Albert National Park, Alberta [21,56]. Peek [203] provides equations for predicting current-year leaf and twig production of beaked hazelnut. Buckman [40] provides equations for predicting hazelnut (beaked hazelnut and American hazelnut) cubic volume based on fuels data collected in northern Minnesota.

Beaked hazelnut can contribute large amounts of fuel where it is dominant. Tappeiner and Alm [257] found mean annual litterfall on a red-pine/beaked hazelnut stand on the Cloquet Forestry Center ranged from 1,730 to 3,720 kg/ha. Litterfall under jack pine/beaked hazelnut was 670 kg/ha greater than litterfall under jack pine alone, and litterfall under red pine/beaked hazelnut was 820 kg/ha more than under red pine without a beak hazelnut understory. Beaked hazelnut density ranged from 30,000 to 50,000 stems/ha the study sites. Biomass estimates are available for beaked hazelnut on the Superior National Forest of Minnesota [104], the Enterprise Forest of Wisconsin [104], and Michigan's Upper Peninsula [67]. Other equations for predicting beaked hazelnut biomass are presented in these sources: [41,226,243,259].

POSTFIRE REGENERATION STRATEGY [251]:
Surface rhizome and/or a chamaephytic root crown in organic soil or on soil surface
Tall shrub, adventitious buds and/or a sprouting root crown
Rhizomatous shrub, rhizome in soil
Initial off-site colonizer (off site, initial community)

FIRE EFFECTS

SPECIES: Corylus cornuta
IMMEDIATE FIRE EFFECT ON PLANT:
Corylus cornuta stems are fire sensitive; even low-severity fire top-kills Corylus cornuta [8,39,58,215,246]. Fires that burn into the organic soil layer may kill root crowns, rhizomes, and/or roots, thereby killing affected clones [7,125,174,258] (see Discussion and Qualification of Fire Effect below).

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Beaked hazelnut rhizomes lie just above mineral soil. They are protected from moderate-severity fire when the organic soil layer is moist, but may be killed when severe ground fire burns into moist soil or when humus is dry [39].

Few studies measure actual fire damage. Lynham and Curran [173], however, reported that beaked hazelnut burned down to 4- to 12- inch (10-30 cm) stem stubs after a crown fire in Quetico Provincial Park, Ontario. Remaining stem stubs were completely charred and dead. Rhizomes and roots were not damaged [173].

PLANT RESPONSE TO FIRE:
Corylus cornuta sprouts from the root crown and/or rhizomes after top-kill [6,39,51,58,95,147,153,158,215,246,272]. Rhizomatous habit greatly increases Corylus cornuta ability to rapidly regain or exceed prefire coverage. Most beaked hazelnut populations are rhizomatous, so they generally recover from most fires more quickly than California hazelnut populations, which generally contain isolated shrubs. Rhizomes are shallow, and Corylus cornuta plants may fail to sprout after ground fires that scorch the rhizomes and/or root crown [174].

There was little documentation of Corylus cornuta postfire seedling establishment as of 2007. Seedling establishment is generally considered rare (review by [246]); however, few postfire studies involve underground organ excavation, which is necessary to distinguish between Corylus cornuta seedlings and sprouts. It is likely that Corylus cornuta establishes at least occasionally on burned sites from nuts stored in animal caches. A few studies conducted in early plant succession suggest that Corylus cornuta establishes from rodent-cached seed [68,221,258]. Tappeiner [256,258] found both beaked hazelnut rodent caches and beaked hazelnut seedlings in young jack pine stands in Minnesota. Further studies are needed to document the frequency of postfire California hazelnut and beaked hazelnut seedling establishment.

Because California hazelnut is usually a minor shrub while beaked hazelnut is often a community dominant, there is far more information on beaked hazelnut's response to fire than there is for California hazelnut.

California hazelnut recovers from low- to moderate-severity fire by sprouting from the root crown. Boyd [33] describes California hazelnut as "an early fire follower". Coverage typically increases through midsuccession. On the H. J. Andrews Experimental Forest in west-central Oregon, California hazelnut showed greatest coverage in "middle" (5-10 years after fire) to "late" (>10 years after fire) postfire succession. Recovery was from root sprouts. California hazelnut was listed as a species of "major magnitude" (>5% cover) in mid- to late postfire succession [114].

Repeated fires may encourage clonal expansion of California hazelnut. In a review, Haeussler and others [111] speculate that continuous California hazelnut colonies in some areas of southern British Columbia are the result of postfire sprouting after repeated wildfires at short return intervals. These populations are at the edge of California hazelnut's northeastern distribution and may be rhizomatous.

No studies documenting California hazelnut postfire seedling establishment were found for this 2007 literature review. However, 1 study suggests that California hazelnut establishes from seed after fire. California hazelnut was absent before logging and postharvest fall burning on the H. J. Andrews Experimental Forest; occurred in trace amounts at postfire year 1 (0.1% cover), and increased to 0.6% cover by postfire year 8 [95]. California hazelnut's method of regeneration was not noted in the study, but prefire absence and the slow increase in California hazelnut's postfire coverage suggests regeneration was from seed, not sprouts.

California hazelnut occurs in early postfire succession, and may persist into late postfire succession in shrubland and woodland sites. It is reported, for example, as a dominant species in late-successional Oregon oak woodlands of the Willamette Valley, where fire has been excluded for 150+ years [33].

As of 2007, information on the seasonal effects of prescribed fire on California hazelnut was lacking, so no seasonal trends were discernible. One study showed a mixed response to fall prescribed fire. California hazelnut on the Teakettle Experimental Forest in the central Sierra Nevada had greater total coverage before fall prescribed burning than 4 years afterwards; however, California hazelnut frequency was similar before prescribed burning and in postfire year 4. Burning was conducted on a mixed-conifer site [285]. Studies are needed to determine possible differences California hazelnut's response to spring vs. fall prescribed fire.

There was also little documentation of the combined effects of fire and logging on California hazelnut. California hazelnut was slightly more common on burn-only treatments compared to burn-and-salvage treatments in a Douglas-fir/tanoak forest on the Klamath National Forest, California. It had 3.4% cover and 57% frequency on burn-only plots and 1.5% cover and 51% frequency on burn-and-salvage plots [122].

Logging, herbicides and fire: On the Coast Ranges of southern Oregon, logging, herbicide spraying, and prescribed fire reduced California hazelnut frequency in the short term. The study site was a Douglas-fir/red alder forest. Prefire Douglas-fir harvest was done in March and April 1974; 2,4,5-T was applied in April 1974; the herbicide dinoseb was applied in July 1974; and prescribed burning was done on 9 August 1974. California hazelnut frequency was 12% in June, after spraying and before fire treatments. In September and November, California hazelnut frequency had declined to 9%. Long-term recovery data were not available; however, California hazelnut was expected to recover rapidly by sprouting [219]. Dinoseb and 2,4,5-T are currently banned [275]; however, other harvest-herbicide-burning treatments may have similar short-term effects on California hazelnut.

In a red alder stand on the Oregon Coast Ranges, summer application of glyphosate followed by fall prescribed fire increased California hazelnut frequency (22%) compared to glyphosate alone (13%), glyphosate and crushing (6%), or soil scarification (3%) [146].

Beaked hazelnut: Postfire sprouting generally increases beaked hazelnut cover over prefire cover following low- to moderate-severity fire, while severe or repeated fires tend to reduce beaked hazelnut coverage [38,39,58,283]. Beaked hazelnut was positively correlated (r=0.56) with tall scorch height on prescribed burn sites on Elk Island National Park, Alberta. Beaked hazelnut sprouted following these fires [31], which were probably of moderate severity. Vegetation surveys conducted on quaking aspen-jack pine-black spruce sites after the 1999 Black River Wildfire in southeastern Manitoba showed beaked hazelnut cover and frequency declined with increasing fire severity [282,283].

Mean cover (%) and frequency (%) of beaked hazelnut sprouts by fire severity classes 1-4 years following the Black River Wildfire [283]
  Lightly scorched Low-severity fire Severe fire
Cover 10.7 1.8 0.4
Frequency 43 26 4

Beaked hazelnut saplings have limited ability to sprout [255] after fires of even light severity because they have not yet developed an extensive rhizome system.

Postfire recovery of beaked hazelnut may be delayed for 2 or more years when the root crown and/or rhizomes are burned [5,6]. Beaked hazelnut showed delayed sprouting after a crowning spring wildfire in a jack pine forest in northeastern Minnesota burned into the organic soil layer and killed root crowns. Most beaked hazelnuts with surviving root crowns sprouted from their root crowns in postfire year 1, while many beaked hazelnuts with dead root crowns sprouted from rhizomes in postfire year 2 [6]. Ahlgren [7] noted that a combination of high soil moisture content and severe fire resulted in higher belowground kill compared to mortality on sites with low soil moisture content. He speculated that steam generated by "intense" fire killed belowground beaked hazelnut tissue [7].

Severe fire or repeated summer fire can reduce beaked hazelnut cover for many years [58,244]. Spurr [244] found that beaked hazelnut thickets converted to red-jack pine forest after "hot" wildfires in the late 19th century.

Seedling establishment is less common than sprouting after fire [153], but seedling establishment is probably important on sites where beaked hazelnut was not present before fire [256]. Several authors note that without frequent fire, sites in northern Minnesota remained occupied by dense beaked hazelnut thickets that precluded beaked hazelnut, red pine, and jack pine seedling establishment [92,118,247]. Postfire vegetation studies on the Superior National Forest showed most postfire beaked hazelnut recovery was from sprouts, although some seedlings were excavated. Beaked hazelnut postfire recovery is shown below. Sprouts and seedlings were not segregated for frequency totals [153]. Since beaked hazelnut was not noted in the earliest postfire surveys, beaked hazelnut recovery on the Keeley Creek Burn may have been from postfire nut dispersal by animals.

Changes in beaked hazelnut frequency after wildfires on the Superior National Forest, Minnesota [153]
  Unburned control Heart Lake Burn (postfire year) Keeley Creek Burn (postfire year)
Year 1956 1965 1954 (3) 1956 (5) 1965 (14) 1956 (2) 1959 (5) 1965 (11)
Frequency (%) 70 57 80 83 73 0 0 3

Beaked hazelnut is most common in early postfire succession. Following the 14 May 1971 Little Sioux Wildfire in northeastern Minnesota, beaked hazelnut biomass increased for 3 postfire growing seasons, leveled off, and increased again in postfire growing season 5 [195].

Mean biomass [195] and height [196] of beaked hazelnut sprouts after the 1971 Little Sioux Wildfire in Minnesota
  Postfire growing season 1 (1971) Postfire growing season 2 (1972) Postfire growing season 3 (1973) Postfire growing season 4 (1974) Postfire growing season 5 (1975)
dry weight (g) 3.09 7.69 13.46 13.62 31.56
height (cm) data not available data not available 60 75 79

During the 5-year study period, beaked hazelnut nitrogen levels remained fairly even; magnesium levels increased for the first postfire growing season and then leveled off; and phosphorus, potassium, and calcium levels increased. See Ohmann and Grigal [196] for quantitative nutrient values.

In Golden Valley, Ontario, paper birch, red maple, and beaked hazelnut dominated new burns and clearcuts, even though the hardwood/beaked hazelnut habitat type was rare in the area. Stocker and others [252] speculated that the paper birch-red maple/beaked hazelnut association is an early successional stage of the sugar maple-yellow birch-eastern hemlock habitat type. In a study of multiple burn sites in a black spruce/balsam fir-northern white-cedar (Thuja occidentalis) forest of northwestern Quebec, beaked hazelnut declined greatly between postfire years 26 and 46, after which postfire coverage remained relatively constant for the next 128 years [71].

Mean beaked hazelnut cover on different-aged burns in northwestern Quebec [71]
Years since fire Cover (%)
26 31.0
46 4.0
74 2.4
120 3.1
143 0.1
167 1.1
174 2.7

Overstory associates that sprout, such as quaking aspen and paper birch, may retard beaked hazelnut postfire recovery. In Minnesota, there were significant differences (P=0.05) in beaked hazelnut sprout production among 33-year-old burns in jack pine, quaking aspen-paper birch, paper birch, and jack pine-paper birch communities. Sprout production was greatest on the jack pine burn and least on the jack pine/paper birch burn, with beaked hazelnut densities of 102,000 (jack pine), 95,470 (quaking aspen-paper birch), 43,330 (paper birch), and 6,150 (jack pine-paper birch) sprouts/milacre [158].

Few studies describe beaked hazelnut postfire recovery in oak (Quercus spp.) savannas. A study in south-central New York found that 1 year after a spring wildfire in a black oak-white oak/Blue Ridge blueberry (Q. velutina-Q. alba/Vaccinium pallidum) community, all beaked hazelnut plants sampled (n=12) had been top-killed and were sprouting. The beaked hazelnuts bore a mean of 4.1 sprouts/root crown [254].

Beaked hazelnut often persists into late postfire succession. In an Isle Royale National Park study, beaked hazelnut was abundant in about 25% of undisturbed paper birch-quaking aspen-balsam fir-white spruce/American fly honeysuckle (Lonicera canadensis) (80-100 years since last fire or other stand-replacing disturbance) and northern white-cedar-balsam fir-paper birch/mountain maple (Acer spicatum) (>200 years since last fire or other stand-replacing disturbance) forests [119].

Beaked hazelnut may retain dominance in late-successional communities with open structure. In wooded quaking aspen-bur oak-green ash (Quercus macrocarpa-Fraxinus pennsylvanica) draws in North Dakota's Turtle Mountains, beaked hazelnut dominated the understories of both unburned and burned sites in late succession, but beaked hazelnut cover was greater on the burned sites. Burn surveys were conducted in 1958, 72 years after a stand-replacing wildfire. Beaked hazelnut cover and frequency (in parentheses) were 55.5% (11.1%) on unburned sites and 79.8% (10.3%) on burned sites [207].

Logging and prescribed fire: Beaked hazelnut showed an initially mixed response to cutting and burning in a jack pine forest on Superior National Forest. Burning was conducted in early June on a site near East Bearskin Lake and in mid-July on a site near Grass Lake. Beaked hazelnut frequency declined greatly 1 year after burning at the Grass Lake site, but increased slightly on the burned East Bearskin Lake site. Cutting alone slightly reduced beaked hazelnut frequency on another East Bearskin Lake site. Beaked hazelnut recovered from all treatments quickly. By posttreatment year 3 beaked hazelnut had recovered much of its prefire frequency on burned sites [8].

Frequency of beaked hazelnut sprouts after cut-and-burn or cut-only treatments [8]
Treatment Frequency (%)

Grass Lake, cut-and-burn treatment
Precut (1962) 97
Postfire year 1 (1963) 37
Postfire year 2 (1964) 73

East Bearskin Lake, cut-and-burn treatment
Precut (1960) 93
Cut & burned (1961) 93
Postfire year 1 (1962) 97
Postfire year 2 (1963) 93
Postfire year 3 (1964) 97

East Bearskin Lake, cut-only treatment
Precut (1960) 100
Postcut year 1 (1961) 93
Postcut year 3 (1963) 83

On the Cloquet Forestry Center, winter logging followed by summer prescribed burning reduced beaked hazelnut density compared to logging alone [200]:

Beaked hazelnut density (stems/m²) the 1st and 2nd seasons after logging on the Cloquet Forestry Center, Minnesota [200]

Treatment

1st season

2nd season
Winter full-tree harvesting Spring full-tree harvesting Control Winter full-tree harvesting Spring full-tree harvesting Winter tree-length harvesting
& summer burn		 Control
10.64a 3.58ab 0.74b 6.74a 5.20a 0.28b 0.77c
For each season, means within the row that are followed by different letters are significantly different (P=0.05).

Method of tree harvest can affect relative beaked hazelnut abundance on postfire salvage sites. One study suggests that single-tree harvest may favor beaked hazelnut. Beaked hazelnut was identified as an indicator species of single-tree retention postfire salvage (indicator value=12.5, P=0.013) on quaking aspen-white spruce-balsam fir wildfire sites in northeastern Alberta. Relative abundance and frequency of beaked hazelnut were 100% and 13%, respectively, on single-tree retention burn plots but were 0% and 0%, respectively, on both patch-retention salvage and no-salvage burn plots [175].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Repeated prescribed fires can reduce beaked hazelnut coverage if there are approximately 8 or fewer years between fires [185,200]. Repeated summer fires probably lower beaked hazelnut ability to sprout by reducing stored food reserves [46]. On the Cutfoot Experimental Forest in north-central Minnesota, spring and summer prescribed burning was conducted in a 90-year-old red pine forest. Plots were burned 1, 2, or 4 times. On all burned plots except repeat-burn summer plots, beaked hazelnut and American hazelnut density increased by at least a factor of 2 compared to unburned plots [38,39]. Hazelnut sprout regrowth is shown below.

Mean density and volume of hazelnut* sprouts after prescribed burning on the Cutfoot Experimental Forest, Minnesota [38,39]
Season and fire frequency Fire years Total density (stems/acre)
in 1961		 Shrubs ≥12 in tall
in 1961		 Volume (ft³/acre)
in 1962

Once burned
   spring 1958 40,400 38,700 829,500
   summer 1958 41,900 38,400 16,200

Twice burned (2-yr intervals)
   spring 1958 & 1960 74,400 63,600 13,200
   summer 1958 & 1960 34,200 18,300 1,600

Quadruple burned (1-yr intervals)
   spring 1958, 1959, 1960, & 1961 95,000 31,500 1,00
   summer 1958, 1959, 1960, & 1961 9,500 800 500
Unburned not applicable 21,600 20,300 38,500
*Pooled data for beaked hazelnut and American hazelnut. Data are means.

On the Slave Lake Forest 100 miles (200 km) north of Edmonton, Alberta, a fall prescribed fire followed by a spring prescribed fire 6 years later reduced beaked hazelnut cover and frequency compared to before the fires. The forest consisted of nearly pure stands of 43-year-old quaking aspen with a beaked hazelnut/bunchberry/wild sarsaparilla understory. Cover (and frequency in parentheses) of beaked hazelnut was 61.2% (48%) before fire, 31.2% (16%) in postfire month 1 following the fall fire, and 4% (4%) the year following the spring reburn [209]. For further information on this study, see the Research Project Summary Understory recovery after burning and reburning quaking aspen stands in central Alberta.

A study on a red pine-white pine plantation on the Kellogg Experimental Forest, Michigan, had similar findings. Beak hazelnut density was reduced by a single May fire compared to the unburned control. In postfire year 4, mean beaked hazelnut densities were 111 stems/ha and 167 stems/ha on burned and control plots, respectively [188]. See the Research Project Summary Effects of surface fires in a mixed red and eastern white pine stand in Michigan for further information.

On the Petawawa Research Forest, Ontario, plots burned by 2 low-severity fires in 2 consecutive years had very little beaked hazelnut the following year. A single severe fire also reduced beaked hazelnut density. See the Research Project Summary of Van Wagner's [277] study for further information.

A combination of top-killing treatments, such as logging and fire or herbicides and fire, may provide more effective beaked hazelnut control than a single treatment method.

Conifer thinning in December 1971 followed by a 17 July 1972 prescribed fire in an Ontario white pine-paper birch-red pine forest greatly reduced beaked hazelnut density and biomass at postfire year 1 compared to pretreatment levels [239,240].

Beaked hazelnut composition before and after treatments on the Petawaw Forest Experiment Station, Ontario. Data are means [239].
  Stems/ha Minimum height
(m)		 Maximum height
(m)		 Biomass
(kg/ha)
Before treatments, sampled
8 Oct. 1971		 45,515 0.55 1.65 1,604
After thinning, sampled
23 May 1972		 16,236 0.58 1.74 716
After thinning and fire, sampled
15 Aug. 1972		 6,563 0.30 0.91 443

FIRE MANAGEMENT CONSIDERATIONS:
Since California hazelnut is a minor shrub and beaked hazelnut often dominant and weedy (see Management Considerations), fire management strategies for the 2 subspecies may be entirely different. Although California hazelnut control may be wanted on some sites, California hazelnut is usually not singled out for control with fire and/or herbicides to the degree beaked hazelnut is. Results of fire research on beaked hazelnut cannot reliably be applied to California hazelnut, since beaked hazelnut is strongly rhizomatous in much of its range and California hazelnut is not.

California hazelnut—
As of 2007, published recommendations for either controlling or promoting California hazelnut with fire were not available. Based upon California hazelnut's ability to sprout from the root crown and its place in early succession, it is likely that frequent prescribed surface fires would benefit California hazelnut.

A single application of fire is unlikely to affect California hazelnut coverage. On the Mt Hood National Forest of Oregon, a spring prescribed fire did not significantly reduce cover of California hazelnut and other shrubs compared to an unburned control in postfire year 1 [228].

Beaked hazelnut—
Beaked hazelnut benefits from prescribed burning at regular intervals, and managers may wish to increase beaked hazelnut coverage in regions where it is a minor or rare plant. Burning every 10+ years would probably maximize beaked hazelnut growth and biomass gain [39],(review by [246]). Fires conducted early in the growing season promote beaked hazelnut growth over fall fires [256].

Beaked hazelnut reduction is wanted on most managed sites. Rapid postfire growth of beaked hazelnut sprouts may interfere with growth of conifer seedlings [8], although pines, particularly jack pine, eventually grow above beaked hazelnut and other shrubs on many sites [9]. Prefire herbicide spraying followed by prescribed burning can greatly reduce beaked hazelnut postfire sprouting [199]. Severe fire or repeat burning at short intervals can also reduce beaked hazelnut coverage. For example, a study in southern Ontario's quaking aspen-jack pine-black spruce forests compared postdisturbance vegetation on sites that had experienced severe, crowning wildfire and on sites that had been clearcut. Beaked hazelnut occurred on both burned and clearcut study plots, but its cover was significantly greater (P<0.05) on clearcuts compared to severe wildfire sites [112].

In the short term, repeated prescribed fire tends to reduce beaked hazelnut biomass while increasing stem density [277]. To date (2007), the effects of repeat prescribed fire on beaked hazelnut have not been documented past 7 years. Such long-term studies are needed, for it is likely that a long series of prescribed fires would reduce beaked hazelnut's rhizome and root carbohydrates, thereby reducing beaked hazelnut's ability to sprout.

Several studies have shown that repeated, moderate-severity surface prescribed fires reduced beaked hazelnut stem biomass [39,68,256]. To optimize beaked hazelnut control, the first 2 repeat burns are conducted 1 or 2 years apart with follow-up burning at <7-year intervals. Pre- or postfire control with herbicides may be required with the first fire if the beaked hazelnut population has a well-established rhizome and root system [68,256]. Repeat prescribed burns without herbicides may be sufficient for controlling beaked hazelnut populations in the seedling or young clonal stages. For young populations, prescribed fire can be used to prevent beaked hazelnut understory dominance of northeastern aspen and pine communities. Tappeiner [258] suggested that in young beaked hazelnut stands, moderate-severity surface fires at 10- to 15-year intervals may prevent beaked hazelnut from obtaining understory dominance. Eliminating nearby seed sources may further retard beaked hazelnut by limiting establishment from off-site seed sources [258]. See Fire Case Studies below for an example application of moderate-severity prescribed fire for beaked hazelnut control.

Using a single severe fire to control beaked hazelnut is not generally recommended. The window of opportunity for conducting prescribed burning at severities sufficient to kill beaked hazelnut rhizomes is short, occurring about 1 week of the year in the Great Lakes region [258]. The prescription would require burning conditions that are usually unacceptable for prescribed fire [16,258].

FIRE CASE STUDIES:

Comparing prescribed fire and 2,4-D use for beaked hazelnut control in northeastern Minnesota
FIRE CASE STUDY CITATION:
Fryer, Janet L. 2007. Comparing prescribed fire and 2,4-D use for beaked hazelnut control in northeastern Minnesota. In: Corylus cornuta. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/ [].

SPECIES INCLUDED IN THE STUDY:
This Fire Case Study contains information on the following subspecies:

Common name Scientific name
beaked hazelnut Corylus cornuta subsp. cornuta

FIRE CASE STUDY REFERENCES:
Unless otherwise indicated, the information in this Fire Case Study comes from the following studies:

Dahlman, R. A. 1991. Comparison of fires and 2,4-D for control of Corylus cornuta (beaked hazel). Minneapolis, MN: University of Minnesota. 47 p. Thesis. [68].

Tappeiner, J. C., II. 1979. Effect of fire and 2,4-D on the early stages of beaked hazel (Corylus cornuta) understories. Weed Science. 27(2): 162-166. [256].

STUDY LOCATION:
This study was conducted on the University of Minnesota's Cloquet Forestry Center, located on the western edge of Cloquet [68,256].

SITE DESCRIPTION:
Study sites are on well-drained soils in the Omega series. The soils are strongly acid, with a pH range of 4.5 to 5.5. Soil texture is fine-loamy to loamy sand 10 to 20 inches deep over a sand layer. Topography is nearly level with occasional rolling glacial outwashes and lake plains [68].

PREFIRE PLANT COMMUNITY:
Study plots were in a mixed jack pine-red-eastern white pine/beaked hazelnut/bigleaf aster (Pinus resinosa-P. banksiana P. strobus/Corylus cornuta var. cornuta/Eurybia macrophylla) community and on mixed pine plantations. Plots were located on stands in early succession, with stands ranging from 40 to 70 years of age [256]. Plot data from the natural community and the plantations were pooled for analyses [68,256]. Site productivity was medium, with mean tree basal area of 180 feet² and densities of 400 to 1,400 trees/acre. Trees ranged from 2 to 14 inches in diameter and 40 to 70 feet tall. Associated trees included quaking aspen (Populus tremuloides) and paper birch (Betula papyrifera); associated shrubs included bush-honeysuckle (Diervilla lonicera), serviceberry (Amelanchier spp.), and low sweet blueberry (Vaccinium angustifolium); associated herbs included western bracken fern (Pteridium aquilinum), false lily-of-the-valley (Maianthemum canadense), and bunchberry (Cornus canadensis) [68]. Mean annual litterfall on the study sites is approximately 1,760 lbs/acre, which allows enough litter build-up to carry fire for at least 2 consecutive years [256].

Beaked hazelnut plants were segregated into 3 size classes prior to burning:

Beaked hazelnut stand structure in the pine understories [68]
Size class Seedlings Small clones Large clones
age (years) 1-12 6-20 20-40+
Clone diameter (inches) <0.1 0.1-2 6-60+
Number of aerial stems 1 1-3 3-25+
Aerial stem height (inches) 2-14 14-24 20-100+
Rhizome diameter (mm) <0.1 2-5 6-25
Clones/acre 300-600 180-400 100-200

Study sites are classified in the following plant community and likely experienced the historic fire regime described below:

Fire regime information on the plant community in which beaked hazelnut occurred in this study. Fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Model [161]. This vegetation model was developed by local experts using available literature, local data, and expert opinion as documented in the PDF file linked below.
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
Jack pine-open lands (frequent fire-return interval) Replacement 83% 26 10 100
Mixed 17% 125 10 100
*Fire Severities:
Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects [117,160].

SPECIES PHENOLOGY:
Beaked

hazelnut aerial stems were expanding rapidly just before the June fires and had nearly ceased growth just before the July and August fires [68].

FIRE SEASON/SEVERITY CLASSIFICATION:
Spring/moderate severity
Summer/low severity

FIRE DESCRIPTION:
Fire management objective: The overall study objective was to determine if beaked hazelnut development and spread in early successional jack pine-red pine-eastern white pine understories can be stopped or slowed with control treatments. Specific objectives were [68]:

1) Determine the effects of fire and light applications of 2,4-D on beaked hazelnut plants at the seedling, small clone, and large clone stages of development (see cautionary statement in Study Applications).

2) Compare seasonal effects of fire and herbicide treatments at these phenological stages: early June during stem and leaf elongation, mid-July when shoot growth stops, and August when plants are near dormancy.

3) Determine the effects of 1, 2, and 3 consecutive annual fires on beaked hazelnut in seedling, small clone, and large clone stages of development.

Fire prescription and behavior: Treatments began in 1970 and were finished in 1971. Prescribed burning was conducted as close to 5 June, 5 July, and 15 August as weather and fuel conditions permitted. A total of 12 plots were burned. Plots were paired for treatments: 2 each in June, July, and August of each year. Summer burn treatments were repeated on 3 of the 6 paired plots. Burning was conducted as close as possible to the target 5 June, 5 July, and 15 August dates, after 3 or more days without rain. Backing surface fires were ignited in afternoon under light, steady winds. The prescription was formulated to minimize fire intensity, assure ease of control, and provide a wide window of opportunity for application. Heat tablets buried in the duff layer showed temperatures on the forest floor exceeded 125 °F only once during burning [68,256].

Fire weather for the paired burns [68]
Plots Date of fire Days since rain Relative humidity (%) Windspeed (mph) and direction Air temperature (°F)
A & B 8 June 1970 10 40 14 SW 89
C & D 7 July 1970 4 45 12 SW 89
3 June 1971 9 37 6 NW 85
23 May 1972 3 39 6 SE 82
E & F 10 Aug. 1970 11 33 5 S 86
12 Aug. 1971 3 44 12 NW 84
G & H 2 June 1971 8 42 3 SW 78
17 May 1972 4 31 6 SW 89
I & J  9 July 1971 3 41 7 NW 82
L & K  26 Aug. 1971 3 37 3 SE 72

HERBICIDE USE:
A total of 14 plots were sprayed with 2,4-D. In 1970, 6 plots were sprayed at the rate of 1 lb/acre: 2 plots each in June, July, and August. In August 1970, 2 additional plots were treated at a rate of 0.5 lb/acre. Six more plots were sprayed in June, July, and August 1972 at 1 lb/acre and 0.5 lb/acre: 2 for each herbicide concentration in June, July, and August. None of the spray plots was retreated [68,256].

FIRE EFFECTS ON TARGET SPECIES:
Fire management objective: Posttreatment data were collected in the August following treatment. Minimum accepted significance level was P<0.05 for all statistical analyses [68,256]. Criteria used to evaluate treatment results were [68]:

1) the proportion of beaked hazelnut clones in each size class that were killed (failure to show signs of life 1 year after treatment)

2) the ratio of live stems (surviving stems and new sprouts) 1 year after treatment to live stems present before treatment

3) the ratio of total length of live stems 1 year after treatment to total length of live stems before treatment

Fire effects: The first and second fires reduced the litter layer appreciably. The first fire consumed about half of the litter layer, and the second fire consumed about one-third of remaining litter. The third fire was discontinuous because there was not enough fuel left on the forest floor for it to carry. Since most fires did not burn into organic soil, beaked hazelnut rhizomes were largely unaffected by the fires. None of the fires did visible damage to overstory trees [68].

In general, 2,4-D caused more beaked hazelnut mortality than prescribed burning [256] (see Herbicide Effects on Target Species). Fire top-killed most large clones, top-killed some small clones and killed others, and killed most seedlings. Top-killed clones sprouted from rhizomes. High mortality of small plants was likely, since seedlings and small clones lack rhizomes and have an undeveloped root system and few food reserves. All fire treatments gave some beaked hazelnut control in all 3 size classes, however, either from direct mortality or removal of seed-bearing-age aerial stems.

Beaked hazelnut mortality increased for all size classes with repeated burning [256]. The first fires caused high seedling mortality (x=74% for June, July, and August fires), some small clone mortality (x=38% for the 3 fires), and mortality of a few large clones (x=8% for the 3 fires). Beaked hazelnut mortality was significantly higher in June than July or August for all size classes after the first fire. A second fire increased beaked hazelnut seedling mortality to 89%: the same level of mortality as that of seedlings sprayed at the 0.5 kg/ha concentration [256]. The second fire significantly increased mortality of beak hazelnut seedlings and small clones above mortalities from the first fires. Large clone mortality did not significantly increase with repeated fires. Aerial stem densities increased an average of 160% for large clones. The biggest increase in large clone density (230%) followed the August fires [68].

Beaked hazelnut mortality varied across plots. On some plots, a single fire resulted in higher seedling and small clone mortality than 2 repeated fires on other plots. On 2 plots, thick, nearly pure pine litter supported an intense fire that killed all beaked hazelnut seedlings and saplings and 90% of large clones [256].

Beaked hazelnut survival after 1 fire. Data are means [68,256].

Seedlings
  Control June fire July fire August fire
Mortality (%) 5.3 80.3 75.8 59.2
Number of aerial stems before/after treatment 40/39 111/9 109/29 296/130
Stem length (inches) before/after treatment 9.5/11.5 7.4/3.2 5.2/1.1 6.5/2.1

Small clones
Mortality (%) 4.0 54.3 41.1 28.2
Number of aerial stems before/after treatment 53/65 71/13 77/40 125/100
Stem length (inches) before/after treatment 36.7/65.0 17.8/6.7 13.0/3.4 15.26.4

Large clones
Mortality (%) 0 16.0 4.2 4.4
Number of aerial stems before/after treatment 98/88 364/418 281/409 290/666
Stem length (inches) before/after treatment 22.6/27.7 1.4/6.3 18.7/7.0 20.1/11.6

Beaked hazelnut response after repeated fires. Data are means [68,256].

Seedlings
  Control 1 fire 2 fires 3 fires
Mortality (%) 5.3 74a* 89b 87b
Number of aerial stems before/after treatment 40/39 296/130 240/32 120/7
Stem length (inches) before/after treatment 9.5/11.5 6.5/2.1 8.2/2.9 15.9/2.3

Small clones
Mortality (%) 4.0 38a 63b 54b
Number of aerial stems before/after treatment 53/65 273/153 257/104 47/14
Stem length (inches) before/after treatment 36.7/65.0 15.2/5.5 28.3/7.0 40.4/5.2

Large clones
Mortality (%) 0 8a 17a 18a
Number of aerial stems before/after treatment 98/88 935/1,493 765/1,223 226/153
Stem length (inches) before/after treatment 22.6/27.7 16.5/8.2 19.2/5.2 12.0/1.7
*Within a size class, means followed by a different letter are significantly different (P=0.05).

HERBICIDE EFFECTS ON TARGET SPECIES:
Herbicide was as effective or more effective than prescribed fire in controlling beaked hazelnut in all 3 size classes. One-half pound of 2,4-D/acre killed nearly as many seedlings and small clones as 1 pound/acre. For large clones, mortality was greatest (93%) with July or August application at 1 lb/acre. At the 1 lb/acre concentration, July and August spraying, when stem growth was slow, caused significantly greater mortality than June spraying, when stems were actively expanding. Weather affected large and small beaked hazelnut clones differently. Herbicide mortality was greatest for seedlings and small clones during the moister conditions of 1971, but large clone mortality was greatest in 1972, the relatively dry year [256].

Spraying also affected associated species, ranging from minor damage to herbaceous species to complete kill of paper birch seedlings [68]. No "major shift" in herbaceous species composition was apparent by the third postspray growing season [256]. See Dahlman [68] for details of effects of 2,4-D on species other than beaked hazelnut.

Beaked hazelnut response after 2,4-D spraying. Data are means [68,256].

Seedlings
  Control 0.5 lb/acre

1 lb/acre
Mortality (%) 5 89a* 88a (June)
97b (July & Aug.)**
Number of aerial stems before/after treatment*** 40/39 275/25 489/29
Stem length (inches) before/after treatment*** 9.5/11.5 15.3/6.5 17.8/14.9

Small clones
Mortality (%) 4 87a 84a (June)
95b (July & Aug.)
Number of aerial stems before/after treatment 53/65 320/34 564/43
Stem length (inches) before/after treatment 65.6/111.4 43.4/6.5 21.9/15.4

Large clones
Mortality (%) 0 74a 55b (June)
93c (July & Aug.)
Number of aerial stems before/after treatment 98/88 601/112 1,028/161
Stem length (inches) before/after treatment 22.6/27.7 14.2/6.5 11.9/4.7
*Within a size class, means followed by a different letter are significantly different (P=0.05).
**Mortality data are pooled for July and August treatments.
***Stem number and length data are pooled for June, July, and August treatments.

In the spring of 1973, which was 1 year or more after all treatments, 5 to 10 beaked hazelnut seedlings were found on some fire and herbicide plots [68,256].

FIRE MANAGEMENT IMPLICATIONS:
Fire management objective: This study demonstrated that beaked hazelnut can be controlled in its early stages of development with repeated late spring or summer prescribed fire, a light application of 2,4-D in late spring, or a heavier application of 2,4-D in summer.

Study applications: Prescribed fire can be a viable alternative to using herbicides to control beaked hazelnut in jack pine-red pine communities and plantations. To control beaked hazelnut in these communities, the authors recommend burning the understory once or twice in summer or spraying with herbicide in June, July, or August. Herbicide recommendations can change as herbicide technology develops. Although 2,4-D was used in this 1970s study, it may not be the current herbicide of choice [68]. Unlike herbicide recommendations, the fire prescriptions and plant responses reported in this study are unlikely to go out-of-date.

Unsurprisingly, this study showed that a high concentration of herbicide causes greater mortality in all size classes of beaked hazelnut than either a lower concentration of herbicide or prescribed fire. A less concentrated herbicide may cause high mortality of seedlings and small clones, but large clones will probably survive. A lower concentration of herbicide releases less herbicide into the environment, thereby reducing herbicide kill of nontarget species. Low- to moderate-severity summer fire is likely to give beaked hazelnut control similar to that of lower-concentration spraying, with a repeat fire needed in most cases. Fire will probably create a more variable landscape than spraying, with a mosaic of herbaceous vegetation, small beaked hazelnut clones, and large beaked hazelnut clones [68,256]. The occurrence of beaked hazelnut seedlings in postfire and postspray year 1 underscores the importance of follow-up treatments to control beaked hazelnut. Since seedlings start producing rhizomes around age 7 to 12 (see Growth), frequent prescribed fires are required to control beaked hazelnut and maintain an open understory. After initial beaked hazelnut control is obtained, Tappeiner [256] recommends burning every 8 to 12 years or spraying every 15 to 20 years to prevent a dense beaked hazelnut thicket from establishing. After initial control, repeat prescribed fires can be of low severity, damaging neither the pine crowns nor leaving fire scars on pine stem bases [256].

Frequent low-severity surface fires, beginning early in stand development, would likely prevent a dense beaked hazelnut understory from developing [68]. Since the third fire did not greatly increase beaked hazelnut mortality in this study, Tappeiner [256] concluded that 2 consecutive fires will probably be sufficient for initial beaked hazelnut control for stands in early succession. Additionally, a third fire may be difficult to carry because of sparse fuels. Two annual burns may cause >80% mortality of beaked hazelnut seedlings and around 60% mortality of small clones.

Litter layers beneath pine/beaked hazelnut sites were moister than litter on sites without beaked hazelnut, and fire was discontinuous on some pine/beaked hazelnut plots. If a third fire is needed for initial control, Dahlman [68] suggests a delay of 2 to 3 years between the second and third fires to allow fuel buildup on the forest floor.

Fire effects will vary considerably in stands similar to those in this study because of variation in litter, live herbaceous vegetation fuel loads, and weather at time of burning. A single application of fire may control beaked hazelnut in dry years or on sites with heavy litter build-up. Tappeiner recommends evaluating the effects of a single fire before deciding to reburn [256].

Where a dense beaked hazelnut understory and/or large beaked hazelnut clones already exist, herbicides may be required to reduce the beaked hazelnut understory before fire is introduced on a regular basis. Once large clones are killed, follow-up prescribed fire and/or spraying can control young beaked hazelnut plants. In consecutive early June fires, the first fire will probably kill most seedlings and kill some small clones. The second fire will probably maximize small clone death. Follow-up herbicide spraying after the first fire would provide similar control [68].

Based on high mortality of seedlings and small clones in this study, frequent, low-intensity surface fires may have been more important than previously recognized in controlling beaked hazelnut in the understories of presettlement red pine-jack pine stands [68,256]. Low-intensity fires such as those used in this study are unlikely to leave fire scars on the pines, so they are not recorded for fire history studies [68]. Other researchers [92,244] have noted that historically, several surface fires occurred in red pine-jack pine stands before a stand-replacement fire. Tappeiner [256] stated that "fire scars in the base of old red pine are a good record of fire history, but they may not be a complete record with regard to control of beaked hazelnut and conifer stand establishment."

Herbicide Precautionary Statement

This Fire Case Study reports research involving herbicides. All uses of pesticides must be registered by appropriate State and/or Federal agencies before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife--if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers.

MANAGEMENT CONSIDERATIONS

SPECIES: Corylus cornuta
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
California hazelnut— Livestock use of California hazelnut is variable. Dayton [70] reports that cattle and domestic sheep browse California hazelnut extensively on some rangelands but use it lightly or not at all on other sites. Use may be light if more palatable browse is available [234]. Limited abundance in most areas generally makes California hazelnut an unimportant browse species [70]; however, livestock may browse California hazelnut heavily where it is abundant.

Wildlife use of California hazelnut browse is generally low to moderate [234]. Mule deer make only light use of California hazelnut browse when more palatable browse is available. Even new sprouts may not be selected. There was no significant difference (P<0.05) in mule deer utilization of California hazelnut before or after thinning and burning treatment in giant sequoia stands in Whittaker Forest Research Station, California, although mule deer use of some associated shrubs increased greatly after posttreatment sproutings [165].

Many birds and mammals consume California hazelnut seeds including Steller's jays, Douglas's squirrels, and golden-mantled ground squirrels [276]. California hazelnut seeds are especially important to squirrels and other acorn-eating animals in times of oak (Quercus spp.) acorn crop failure [49].

Beaked hazelnut—Information on livestock use of beaked hazelnut was not found in the literature.

Beaked hazelnut is browse tolerant [29], and a variety of wildlife species utilize beaked hazelnut browse and nuts (reviews by [111,246]). Deer, moose, and elk consume the browse, especially in winter [134,289],(review by [246]). Snowshoe hares utilized beaked hazelnut browse moderately to heavily on Manitoulin Island, Ontario [72]. High availability makes beaked hazelnut important year-round forage on many sites in the Great Lakes states and the Northeast, even though it is not generally preferred (review by [246]),[247].

Moose and elk may browse beaked hazelnut heavily on some sites. A study in Riding Mountain National Park found elk and moose browsed beaked hazelnut seasonally, as a winter food, and year-round. Although beaked hazelnut use was less than other shrubs based on relative abundance, its total browse use was higher than all shrubs except willows (Salix spp.) [225]. Moose utilization of beaked hazelnut is generally moderate to heavy in winter [24,26,140,143,202], while moose use is usually light to nonexistent in other seasons [140,202]. A study on the Little Sioux Burn near Ely, Minnesota, showed that in postfire year 2, moose browsed beaked hazelnut sprouts "moderately" from October through December, browsed them "lightly" in spring, and did not use beaked hazelnut in summer [140].

American beavers prefer beaked hazelnut browse [75]. In Ontario, beaked hazelnut was among the top 6 browse species selected by American beavers [76], and beaked hazelnut was browsed more often than expected (P<0.05) by American beavers in Michigan [27]. American beavers may locally influence forest structure by reducing relative abundance of beaked hazelnut and other palatable browse species and increasing relative abundance of conifers [75].

On the Cloquet Forestry Center, beaked hazelnut buds and catkins generally ranked second to quaking aspen catkins in use as winter and early spring ruffed grouse foods, ranking first on some sites [109].

American black bears, many small mammal species, and many bird species consume beaked hazelnut seeds [35,223],(review by [246]). Near Edmonton, New York, researchers found red squirrel middens containing nothing but beaked hazelnut seeds [148]. Wild turkeys also eat the nuts [99].

Beaked hazelnut understories provide habitat for a variety of bird species in quaking aspen forests of the North [131]. On the Cloquet Forestry Center, Magnus [177] found quaking aspen-paper birch/beaked hazelnut communities were prime ruffed grouse habitat in all seasons.

Palatability:
California hazelnut is fairly palatable to domestic goats and mule deer and generally unpalatable to domestic sheep, cattle, and horses [234,272]. Hairy leaf texture probably reduces California hazelnut's palatability [272]. Sprouts may be closely browsed for a few years, however [234]. Palatability of California hazelnut sprouts declines with stem age. In a 1964 browse utilization survey of the repeat Tillamook Burns (1933-1945) of Oregon, Columbian black-tailed deer only grazed California hazelnut sprouts when green forage was unavailable in winter [64].

Beaked hazelnut is moderately palatable to most wild ungulates. It is rated unpalatable to moderately palatable for white-tailed deer [129]. It is important white-tailed deer forage in the Great Lakes states, however, due to its abundance [247],(review by [246]). A study on the Superior National Forest, Minnesota, found white-tailed deer used beaked hazelnut slightly less than expected based on availability [73]. A similar study in New Brunswick study found white-tailed deer and snowshoe hares browsed beaked hazelnut less than expected based upon availability [262].

White-tailed deer prefer beaked hazelnut sprouts over old stems. A study on a northern Minnesota quaking aspen burn found white-tailed deer and moose were concentrated in areas with large amounts of hardwood sprouts, including beaked hazelnut. Greatest use was in late fall, although spring browse was also used heavily [139].

Productivity estimates: Grigal and others [104,197] give estimates of browse production of beaked hazelnut and other shrubs on the Superior National Forest. Peek [203] provides equations for predicting current-year browse production of beaked hazelnut. Beuch and Rugg [42] present biomass equations for predicting availability of beaked hazelnut and other shrubs that provide American beaver forage.

Nutritional value:
California hazelnut— Little information was available on the nutritional value of California hazelnut. For nutritional analysis of California hazelnut browse on the Tillamook Burn of Oregon, see Radwan and Crouch [211]. California hazelnut samples were collected 18 years after the last of 4 repeat wildfires [211].

Beaked hazelnut— For information on nutritional and energy values of beaked hazelnut browse, see these sources: [1,55,96,104,105,182,201,259].

Beaked hazelnut seeds are a nutritious food for birds, rodents, white-tailed deer, and American black bears [35,223],(review by [246]). The seeds are richer in protein (26.5%) and fats (61.4%) and lower in carbohydrates (7.2%) than the seeds of associated beeches (Fagus spp.) and oaks. Buds and male catkins are protein-rich foods of ruffed grouse [107], (review by [246]).

Cover value:
California hazelnut— Little information was available on wildlife use of California hazelnut as cover. White-footed voles, which have G3 (vulnerable) protection status, were positively correlated with California hazelnut (r=0.86, P=0.0004) on the Umpqua National Forest of southwestern Oregon [180].

Lattin and Wetherill [164] inventoried herbivorous insects living on California hazelnut in western Oregon. A beetle, the hazelnut weevil, is an obligate California hazelnut feeder. For an account of the hazelnut weevil's life history, see Treadwell and Storch [269].

Beaked hazelnut— Beaked hazelnut thickets provide cover for white-tailed deer, rabbits and other small mammals, American woodcocks, and grouse (review by [246]),[133]. On the Cloquet Forestry Center, survival of male ruffed grouse during mating season was associated with drumming logs located next to dense beaked hazelnut cover [108].

VALUE FOR REHABILITATION OF DISTURBED SITES:
Corylus cornuta is used for wildlife, shelterbelt, and restoration plantings. For reviews of nursery procedures for cultivating Corylus cornuta, see these sources: [20,53,246].

California hazelnut is resistant to laminated root rot (Phellinus weirii). California hazelnut and other nonhost shrubs are planted in the Pacific Northwest to increase biodiversity and reduce rates of laminated root rot infection in Douglas-fir and fir-spruce (Abies-Picea spp.) forests [100].

OTHER USES:
Corylus cornuta nuts are palatable to humans [10]. Nut production of wild Corylus cornuta shrubs is sparse compared to European filbert and other commercial hazelnuts (Corylus spp.) [52]. However, Corylus cornuta is used in hazelnut breeding programs to produce high-yield, disease-resistant hybrid cultivars. California hazelnut and beaked hazelnut show more genetic resistance to eastern filbert blight fungus than commercial hazelnuts [63]. Beaked hazelnut from the southern Canadian provinces is used to breed cold-resistant hazelnut cultivars [84].

Native American use: Native Americans ate California hazelnut nuts [13,33,57,159,159] and used them for trading [137,159]. Lewis and Clark and the botanist Douglas, for example, bartered with local tribes for California hazelnut seeds [137].

Native Americans used California hazelnut sprouts for making fish traps [57,271], baskets [13,57,215,271,296], and baby carriers [57]. The wood was used for implements [296]. Native Americans used California hazelnut medically as an emetic, a wormer, an astringent, and for teething (review by [88]).

OTHER MANAGEMENT CONSIDERATIONS:
California hazelnut— California hazelnut may interfere with establishment and growth of conifer seedlings [39,260]. Herbicides are sometimes used on California hazelnut and other shrubs to reduce interference with conifer growth [133,260]. In Oregon and Washington trials, complete California hazelnut kill was reported with triclopyr. California hazelnut was top-killed but sprouted after 2-4-D application [137]. The Washington State Cooperative Extension Service [284] provides a list of herbicides registered for use on California hazelnut and provides recommendations for herbicide concentrations, seasons of application, and application methods.

Few studies documented California hazelnut response to logging as of 2007. Since California hazelnut is nonrhizomatous, large population increases are unlikely after logging. A study on the Fort Lewis Military Reservation, Washington, showed little difference in California hazelnut abundance on thinned and unthinned second-growth Douglas-fir stands. Both stands originated after clearcutting in the 1940s and had never burned. The thinned site was first logged in the early 1970s and again in the late 1980s. In 1991 to 1992 surveys, California hazelnut cover and frequency were 2.4% and 45.8%, respectively, on the unthinned site and 3.5% and 45.0%, respectively, on the thinned site [266].

Beaked hazelnut—Beaked hazelnut plays an important role in nutrient recycling in forests of the Great Lakes States and the Northeast [59,257]. In 50- to 60-year-old red pine-paper birch/beaked hazelnut stands on the Cloquet Forestry Center, beaked hazelnut litter contributed high levels of nitrogen, calcium, and magnesium to the forest floor. Its litter decomposed relatively rapidly, so the nutrients were recycled quickly [257].

Beaked hazelnut density is increasing in many red pine-eastern white pine-jack pine forests of the northern United States and southern Canada, while pine (Pinus spp.) recruitment is dwindling [73]. Rapid growth makes beaked hazelnut highly competitive for light and soil moisture, so beaked hazelnut may interfere with growth of young conifers [46,89,111,152,166,187,218]. Hsiung [135] reports that on the Cloquet Forestry Center, wherever beaked hazelnut occurs "the soil is dominantly occupied by its underground system". Beaked hazelnut has been widely blamed for poor conifer regeneration and growth in the Northeast [152,162,166,204,218]. Eyre and others [82,204], for example, called beaked hazelnut and American hazelnut the "worst offenders" in hindering red pine reproduction and growth, and Perala [204] stated that beaked hazelnut "grows aggressively in nearly every upland timber type" in Minnesota. Theories for beaked hazelnut "invasion" or sometimes near-monocultural dominance in conifer forest understories include altered fire regimes, increases in white-tailed deer density above historic numbers and a concomitant increase in browsing pressure on pines, harvest of old-growth pines, white pine blister rust infection of eastern white pine, and a combination of those factors [151,247]. In the 1960s and 1970s, beaked hazelnut was heavily treated with herbicides on many sites to reduce "competition" with pine seedlings (for example, see these sources: [151,222]); however, pine recruitment generally did not increase despite herbicide reduction of beaked hazelnut. In a browsing effects experiment in the late 1980s at Itasca Sate Park, Steingraber [247] found that white-tailed deer browsing pressure on eastern white pine and beaked hazelnut was similar (about 85% utilization outside exclosures). Beaked hazelnut was better able to recover from browsing, however. Beaked hazelnut sprouted from rhizomes after browsing, producing a few rapidly elongating sprouts/root crown. Lacking ability to sprout after browsing, eastern white pine density decreased outside exclosures [247]. This study suggests that white-tailed deer browsing is at least partially responsible for the decline in pine recruitment. Further studies are needed to determine the interactive effects fire and other factors affecting pine recruitment and beaked hazelnut density.

Browsing response: Beaked hazelnut may increase or decrease with heavy browsing, probably depending upon availability of other, more palatable shrubs. Beaked hazelnut was among 10 shrub "extreme increasers" on white-tailed deer winter rangeland in northern white-cedar swampland of Wisconsin. The white-tailed deer population was high, and northern white-cedar harvest and swamp draining had reduced available white-tailed deer habitat [110]. However, other studies show large decreases in beaked hazelnut after heavy browsing pressure. White-tailed deer and moose have apparently eliminated beaked hazelnut from most of Newfoundland's Anticosti Island. Beaked hazelnut only grows there on rock slides that deer and moose cannot access, although in the early 1900s it was abundant enough to supply local residents with a reliable source of nuts [205]. In Itasca State Park, heavy white-tailed deer browsing reduced beaked hazelnut to "sparse" coverage in the late 1930s [224].

Control: There is considerable interest in controlling beaked hazelnut due to its potential to interfere with conifer seedling growth. Beaked hazelnut can be controlled with 2,4-D, glyphosate, triclopyr, or hexazinone [46,58,111,189,199,204,206,249,250,281]. Repeated applications are usually needed to control sprouts [58,250,260]. See Michigan State University and other Cooperative Extension Agencies for details on herbicide control of beaked hazelnut.

Mechanical treatments such as clipping, rock raking, disking, or scarification are largely ineffective for beaked hazelnut control, and they are potentially detrimental to site quality [68]. Disking or other mechanical treatments may reduce stem density for a few years but ultimately result in beaked hazelnut densities above pretreatment levels unless the rhizomes and root crowns are removed (review by [111]),[58]. Deep disking or deep trenching have successfully reduced beaked hazelnut cover and frequency [58].

On an Ontario jack pine plantation, brushsawing increased beaked hazelnut density when compared to untreated plots, while glyphosate spraying provided effective control. Data were collected in posttreatment year 3. Both single and multiple glyphosate treatments significantly decreased beaked hazelnut cover (P=0.05), with multiple treatments giving greatest control. Although brushsawing was not effective on beaked hazelnut due prolific postcut sprouting, it reduced density of some associated shrubs. Jack pine seedling growth was significantly greater on brushsaw and herbicide treatment plots compared to untreated plots (P≤0.05) [178,179].

Nonnative invasive threat: Beaked hazelnut understories in boreal ecosystems are vulnerable to invasion by nonnative Siberian peashrub (Caragana arborescens). Siberian peashrub can achieve "dominance equal to or more than the naturally dominant beaked hazel" [127].

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