Fire Effects Information System (FEIS)

FEIS Home Page

Hedera helix

• INTRODUCTORY
• DISTRIBUTION AND OCCURRENCE
• BOTANICAL AND ECOLOGICAL CHARACTERISTICS
• FIRE EFFECTS AND MANAGEMENT
• MANAGEMENT CONSIDERATIONS
• APPENDIX: FIRE REGIME TABLE
• REFERENCES

INTRODUCTORY

AUTHORSHIP AND CITATION FEIS ABBREVIATION NRCS PLANT CODE COMMON NAMES TAXONOMY SYNONYMS LIFE FORM

Photo by Chuck Bargeron, University of Georgia, Bugwood.org

Two subspecies of English ivy are recognized in Europe [70]:

H. helix L. subsp. canariensis (Willd.) Cout.
H. helix L. subsp. helix

English ivy has numerous cultivars [30,31,89,186]. The American Ivy League indicates there are 400 distinct cultivars developed in North America and other countries that are distinguished primarily by their morphology, growth rate, and hardiness to adverse growing conditions (e.g., full sun, cold temperatures) [158].

DISTRIBUTION AND OCCURRENCE

• GENERAL DISTRIBUTION
• HABITAT TYPES AND PLANT COMMUNITIES

Based on regional floras [30,46,60,92,103,104,122,186,196], invasive plant publications [25,125,193], and websites [17,45,74,96,101,106,113,149,163,176,177], English ivy is most invasive in the Pacific Northwest. Based on a regional invasive species map, English ivy is not widespread in the Southeast [100], but it may be locally abundant in some mid-Atlantic states including Virginia [115,117], West Virginia, and in some southern states including North Carolina, South Carolina, Alabama, and Arkansas [100]. Several sources indicate that English ivy is not as problematic in the Northeast as in the Pacific Northwest, mid-Atlantic, and Southeast. A review of floristic surveys from the eastern United States found that English ivy occurred in temperate forests in this area but was not common [88]. Local floras indicate that English ivy occasionally escapes cultivation in the Northeast [46,92], and English ivy is not listed on a Northeastern invasive species website [96]. It may, however, be locally abundant in parts of Washington, DC [164,170]. NatureServe provides a map of English ivy's North American distribution.

Brought to North America by colonial settlers [99,125,146], English ivy was first documented in North America in Virginia around 1800 [191]. Since then English ivy has been widely cultivated as an ornamental [90,104,138,184,192], although its cultivation in Hawaii did not begin until the early 1900 [186]. In many places where it is planted, English ivy escapes cultivation to varying degrees [46,92,103,104,122,195] and invades and persists in wildlands [30,60,138,186,190,195].

English Ivy has been introduced to South Africa, India, Australia, New Zealand, Brazil, and Mexico [97,190].

Native range: English ivy is native to Eurasia [46,52,103,104,186,192,196], occurring from the Caucasus Mountains [184,186] to Norway [52,145] and south to Iran [97] and northern Africa [97,184]. It tends to be less abundant north of the Alps [145].

Pacific Northwest and California: In the Pacific Northwest, English ivy occurs in deciduous or conifer-deciduous mixed forests with bigleaf maple (Acer macrophyllum) [66], red alder (Alnus rubra), Oregon ash (Fraxinus latifolia), black cottonwood (Populus balsamifera subsp. trichocarpa), and Oregon white oak (Quercus garryana) [66,111]. It is considered a threat to nearly all forest types in the Pacific Northwest coastal area below 3,000 feet (900 m) [4]. In Oregon, it occurred in a dense conifer-deciduous mixed forest with Douglas-fir (Pseudotsuga menziesii), western redcedar (Thuja plicata), and bigleaf maple ([66],Waggy 2000 personal observation [185]). It is particularly common in forests near populated areas ([4], Waggy 2000 personal observation [185]). In California, it occurs in redwood (Sequoia sempervirens) forests [134,140] and riparian forests dominated by Fremont cottonwood (Populus fremontii), white alder (Alnus rhombifolia), and willow (Salix spp.) [157].

Southwest: Available information at the time of this writing (2010) indicated that English ivy may not be common in native plant communities in the Southwest. Floras from Texas [30] and Utah [192] indicate English ivy typically occurs as an ornamental around homesites, but it may occasionally escape to wooded areas [30].

Mid-Atlantic and southeastern states: In this portion of North America, English ivy occurs with many species of deciduous trees and does not appear to be closely associated with any specific forest type. Canopy dominants commonly occurring with English ivy include maple (Acer spp.), hickory (Carya spp.), American beech (Fagus grandifolia), ash (Fraxinus spp.), oak (Quercus spp.), sweetgum (Liquidambar styraciflua), yellow-poplar (Liriodendron tulipifera), sycamore (Platanus occidentalis), and American elm (Ulmus americana) [12,43,107,114,116,117,119,156,162,194]. In the southeastern United States, English ivy occurs in pine (Pinus spp.) savanna, tropical hardwood, and baldcypress (Taxodium distichum) communities [156]. In Florida [196] and Georgia [198], English ivy occasionally occurs in disturbed hammocks [196].

In the mid-Atlantic and southeastern United States, English ivy occasionally occurs in plant communities that have been disturbed or may not contain native assemblages. On one site in North Carolina, English ivy occurred in a transitional loblolly pine (Pinus taeda) forest that was likely planted [194]. On a disturbed terrace in South Carolina, English ivy occurred in a forest that contained a mix of deciduous and conifer trees that included river birch (Betula nigra), water oak (Quercus nigra), and Virginia pine (Pinus virginiana) [173]. In Rock Creek Park in Washington, DC, English ivy occurs in an Allegheny blackberry (Rubus allegheniensis) shrubland codominated by nonnative vines including porcelainberry (Ampelopsis brevipedunculata).

Northeast, Great Lakes area, and Canada: At the time of this writing (2010), information pertaining to common plant associates of English ivy in these areas of North America was lacking.

European range: In Europe, English ivy occurs in plant communities similar to those described for North America. It occurs in deciduous forests dominated by maple (Acer spp.), birch (Betula spp.), European beech (Fagus sylvatica), European ash (Fraxinus excelsior), oak (Quercus spp.), littleleaf (Tilia cordata), and wych elm (Ulmus glabra) [22,27,63,65,68,73,75,79,144,170]. English ivy was the dominant groundlayer species in a forest that contained young European ash and sycamore maple (Acer pseudoplatanus) and a mix of old trees including European ash, wych elm, European beech, Norway pine (Abies excelsa), European larch (Larix europaea), spruce (Picea sp.), Scots pine (Pinus sylvestris), European aspen (Populus tremula), and English yew (Taxus baccata) [73]. In France, English ivy was common in an oak and European hornbeam (Carpinus betulus) forest [168]. One study from Great Britain indicated that English ivy was more common in beech than ash forests [36], and a study from France indicated it favored European ash and English oak (Quercus robur) forest over other forest types [136].

The following table is a list of North American plant communities where English ivy occurs.

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

GENERAL BOTANICAL CHARACTERISTICS SEASONAL DEVELOPMENT REGENERATION PROCESSES SITE CHARACTERISTICS SUCCESSIONAL STATUS
	Juvenile growth phase Photo by Chuck Bargeron, University of Georgia, Bugwood.org	Adult growth phase Photo by James H. Miller, Bugwood.org

Aboveground: English ivy is a woody [184], evergreen [30,46,52,60,99,184], trailing or climbing liana [30,92] or shrub [129]. In Europe, English ivy occasionally grows as a tree [97,136].

English ivy has 2 distinct growth phases, the vegetative phase (juvenile) and the sexual reproductive phase (adult) [153].

Individual English ivy plants may have both juvenile and adult stems. The juvenile phase typically forms the ground cover [31,99]. Juvenile English ivy begins to climb when vertical structure is available (e.g., trees, shrubs, buildings, utility poles), and vertical stems transition to the adult phase [97].

As a ground cover, English ivy grows from 6 to 8 inches (10-20 cm) tall [31,99]. Once stems begin climbing, they typically reach 90 feet (30 m) in height [25,31,46,65,99,152,184] but occasionally may climb higher, reaching the tops of 300-foot (90 m) conifers [146]. English ivy climbs with the aid of root-like structures [19,25,31,46,84,152] that exude an adhesive substance [99]. One publication from England indicated that English ivy attaches to substrates by numerous small roots [52]. Branches are typically slender on low-growing plants [99], but climbing and older trailing branches may be 4 [31,135] to 12 inches (10-30 cm) in diameter [25,65,99,146,152], with furrowed bark [31]. Leaves are typically 4 inches (10 cm) long × 2.5 to 5 inches (6.4-13 cm) wide and are 3 to 5 lobed in the juvenile phase and broadly lanceolate and unlobed in the adult phase. Flowers are clustered in umbels on adult stems [99]. There are 8 [182] to 20 [97] flowers/umbel; umbels grow in clusters of 3 [97] to 6 [14]. English ivy fruit is a berry [30,60,104] about 5 [186] to 9 mm long [60,122] and 6 [192] to 9 mm in diameter [145], with an average weight of 281.5 mg [59]. Its fruit contains 2 to 5 seeds [30,31,59,60,145,184] that are about 5.7 × 3.7 mm in size [52].

Belowground: Information from an exotic pest website in the Southeast suggests that English ivy does not form an extensive underground root system [149]. An invasive plant publication from California [126] and a publication suggesting landscaping plants for use in chaparral plant communities to reduce fire hazard [123] suggests that English ivy's roots are generally shallow. In Washington, DC, English ivy root depth ranged from 1 to 4.13 inches (3.0 -10.5 cm) below the soil surface [169]. A study from Spain measured rooting depth for several vines including English ivy and found the average rooting depth for all species was statistically similar (P<0.001); root depth for 100 mg of plant dry mass was 3.8 inches (9.6 cm), and for 1.00 g of plant dry mass it was 6.34 inches (16.1 cm). English ivy roots were highly dissected, and the average root diameter 5 mm from the root tip was 0.45 mm [133].

Stand structure: In woodlands, English ivy frequently forms a dense ground cover that may occupy large areas made up of numerous individuals [97]. In North America, English ivy has been described as forming an "ivy desert" [125]. In the Green River Gorge in North Carolina, English ivy completely covered the ground in a deciduous forest [120]. In floodplain forests along the Rhine River in France, English ivy "carpets" the forest floor until it eventually reaches a tree and begins to ascend [135]. In one study in these forests, average English ivy stem density was 24.5/ha on sites that experience brief annual flooding compared to 61.9/ha on sites where flooding had been excluded. Clumping (more than one English ivy vine/host tree) was common, particularly on trees in the canopy and subcanopy of the forest, largely due to the greater abundance of support in these layers [136]. In another study in the Rhine River floodplain in France, English ivy stem density reached 120 stems/ha in a dense Lombardy poplar (Populus nigra) and English oak forest [135].

Longevity: As of this writing (2010), information pertaining to English ivy's longevity in North America was lacking. In forests along the Rhine River in France, the oldest English ivy vines at 1 site were 50 years old, while the oldest vines at another site were at least 66 years old [136]. There is a report of a 433-year-old stem of English ivy that was over 20 inches (60 cm) in diameter, but it is unclear where it occurred (Schenk 1893 cited in [37]).

English ivy's flowering period in North America is variable; reports range from late spring to fall (see Table). As of this writing (2010), little had been reported on its fruiting period in North America. One report from the Pacific Northwest indicated that English ivy flowers in the fall and fruits in the spring [146]; however, a local flora for that area gives a flowering period of May through June [60]. In the southeastern United States, English ivy fruits from October to May [99].

Available evidence suggests that in its European range, English ivy generally flowers in the fall, and fruit ripens over the winter from December to early spring.

Vegetative regeneration Pollination and breeding system Seed production Seed dispersal Seed banking Germination Seedling establishment and plant growth
	English ivy fruit. Photo by Forest & Kim Starr, U.S. Geological Survey, Bugwood.org

English ivy spreads vegetatively, either by rooting from stems and stem fragments that contact the soil [66,126,146,159,160,190] or from fragmented roots [146]. English ivy reproduces sexually by seed [25,52,77,97,126,146], typically in open or disturbed habitat [97]. In some locations, establishment from seed may be infrequent [16,52].

Vegetative regeneration: Several invasive plant publications [25,126,159,160,190] and one study from North America [13] indicate that English ivy sprouts from stem fragments and cut stumps. Stems [66,146] and stem fragments root easily when they are in contact with the soil [160,190], and plants spread from adventitious roots that develop along the stem [126]. Fragmented roots left in the soil may sprout a new stem [146]. In the United Kingdom, English ivy spreads extensively by vegetative regeneration; establishment from seed may be infrequent [52,97].

Pollination and breeding system: Sexual reproduction typically occurs in climbing adult plants that reach sufficient light, but trailing plants may occasionally produce fruit, especially if they are growing in full sunlight [146]. English ivy flowers are bisexual [122,126], protandrous, and cross-pollinated by a wide variety of insects [52,97,182]. Faegri and van der Pijl [38] speculated that plants that flower late in the year, like English ivy, may be completely dependent on flies for pollination because numerous other insects like bumblebees and bees are not present during that time of year.

In the Netherlands, pollen counts collected from various sampling sites (e.g., water trough, roof tiles, moss on a thatched roof) in October determined that one large, profusely flowering English ivy produced several billion pollen grains annually [14].

Seed production: In France, 741 English ivy seeds were collected in a 427.9 foot² (39.75 m²) plot from December 1981 to May 1983 on a site where English ivy was common in the aboveground vegetation [27]. English ivy's seed production may be limited in cooler climates. Based on an analysis by local researchers, Michigan's Invasive Plant Council does not consider English ivy invasive in the Great Lakes region because seed production may be inconsistent [98]. In Europe, cold weather may prevent early fruit crops from ripening so that no viable seed is produced [145]. In climates like those of the Czech Republic and Slovakia, fruits may not produce seed every year [85]. English ivy fruit size or production may be limited for plants growing above 869 feet (265 m) in elevation (Macleod 1983 cited in [145]).

Seed dispersal: English ivy seed is dispersed by birds [25,60,99,146,159]. In North America, birds that distribute English ivy seed included European starling, cedar waxwing, American robin, Steller's jay, mockingbird, and house sparrow [160]. Snow and Snow [145] provide a list of birds that may act as potential dispersers of English ivy seed in the United Kingdom (see Importance to Wildlife and Livestock). After digesting the fruit, birds may regurgitate English ivy seed one at a time [23]. One literature review suggested that English ivy seed is deposited in bird droppings as well as regurgitated [97]; however, a seed germination study found no evidence that English ivy seed is defecated by birds [23]. Researchers in the Netherlands speculated that English ivy has an 80% chance of being dispersed to a forest if there is a seed source 3 feet (1 m) or less away, but at 3,000 feet (1,000 m) away, the probability decreases to nearly 0% [48].

English ivy phenology may vary for different locations and influence the dates when seed becomes available for dispersal [145]. In the United Kingdom, English ivy seeds are dispersed in early winter (November and December), but early flowering plants likely have their fruit taken sooner [97,145]. In Germany, English ivy seed was dispersed in later spring (Kollman 1994 cited in [76]).

Seed banking: Publications from the United Kingdom indicate that English ivy seed is short-lived and does not form a persistent seed bank [52,97]. Because English ivy's flowering and fruiting is limited by shade (see Pollination and breeding system), accumulation of English ivy seed in woodlands may be an "expensive luxury" [171]. Under experimental conditions, English ivy seed planted in various size containers and soil types continued to germinate for 1 year after planting; however, germination and seedling survival generally declined over time, particularly for seed buried 5 months or longer [152].

English ivy's presence in the aboveground vegetation may not indicate its presence in the seed bank. In deciduous forests in northwestern Greece [22] and Denmark [75], English ivy occasionally occurred in the aboveground vegetation but its seed was not found in the soil seed bank. In a deciduous forest in Spain, English ivy was 1 of 4 dominant shrub species in the understory (3% aboveground cover) but did not appear in the seed bank at samplings depths of up to 4 inches (10 cm) [112].

Germination: Information pertaining to English ivy's germination requirements was incomplete as of 2010. English ivy belongs to a family of plants with seeds containing small embryos, and its seed may be dormant [9]. An invasive species publication indicated that English ivy has a hard seed coat that must be scarified before germination occurs, a process that is likely achieved when English ivy seed passes through a bird's digestive system [126]. Conversely, one publication on berry consumption by birds from the United Kingdom indicated that English ivy seeds are "unusually soft" [145]. Results from a study in western France suggest that English ivy seed requires no scarification for germination. English ivy germination was highest when fruit pulp was removed either manually (97%) or by bird ingestion and subsequent regurgitation (99%) compared to seed left in fresh (53%) or dried fruit (0 %). Because germination was similar when pulp was removed manually or by bird ingestion, researchers speculated that ingestion by birds appeared to have no other effect than pulp removal [23]. Pulp removal may facilitate germination in English ivy [31] by shortening its dormancy requirements [23]. Under cultivation, uncleaned English ivy seed did not germinate immediately or when cold stratified; however, 70% of the seeds germinated once the fruit pulp was removed [31]. In the laboratory, average length of seed dormancy in English ivy ranged from 4.2 weeks to 8.5 weeks; however, dormancy was shortened when fruit pulp was removed [23].

Available evidence suggests that English ivy seed germinates fast and has a high germination capacity. Clergeau [23] reported that about 60% to 100% of English ivy seed germinates in 15 days or less. Nearly 100% of the seed germinated in less than 10 days when fruit pulp was removed from the seed by hand or by bird ingestion [23]. In the laboratory, most viable English ivy seed germinated within 5 to 20 days. Percent germination was from 0% to 92% for variable temperature regimes. Low rates of germination were attributed to high rates of seed decay. English ivy seed not fully ripened before falling from the mother plant was prone to decay [85]. One flora from Texas indicated that English ivy seed usually germinates the 2nd year after it is planted [184].

In a riparian forest in France, short periods of flooding favored English ivy germination but not seedling establishment. Six-month-old English ivy seedlings were significantly (P<0.01) more abundant on a site that experienced brief annual flooding than on a site where flooding had been excluded. However, there was no significant difference in the number of 1-year-old seedlings between the 2 sites. Researchers attributed this to high mortality of English ivy seedlings during the 1st year of growth caused by flooding, "competition", and browsing [136].

Seedling establishment and plant growth: In the United Kingdom, English ivy is considered tolerant of stress and able to establish in a range of environments [52]. A literature review indicated that English ivy seedlings establish on disturbed or open sites [97], although it may not establish well under frequent or severe disturbance [52]. English ivy seedlings may also establish under forest [131,135] or shrub [77] canopy; however, growth rate may be less than for unshaded seedlings. In the greenhouse, English ivy's relative growth rate for potted seedlings was significantly less (P=0.001) for plants in neutral shade (3.5% daylight) than for plants in 35% daylight. English ivy seedlings were moderately tolerant of shade under drought conditions [132]. On an experimental site in England, English ivy seedling density was positively correlated with soil moisture (r²= 0.65) and was highest under shrubs associated with relatively high soil moisture content [77]. Researchers in Spain reported a greater than 90% survival rate for English ivy seedlings after 1 year (Laskurain and others cited in [66]).

Seedlings are shallowly rooted and grow a single, slender, vertical primary root that bears many short, fine branches, some of which develop into horizontal secondary and lateral stems [97]. English ivy has 2 distinct growth phases (see Botanical description); plants in the juvenile phase are adapted to shade [97,136] and remain vegetative, while plants in the adult growth phase occur in the sun and flower. Juvenile plants root from the nodes of the aboveground creeping stem [97] and grow rapidly along the ground [146]. A publication from North America suggests that the juvenile period is long, often lasting 10 years or more [126]. English ivy begins to climb when it reaches a vertical structure [146], taking approximately 30 to 40 years to reach tree canopies, but growth may be faster on flooded sites [136]. Both trailing and climbing vines spread by rooting at the nodes [99]. Juveniles climbing small hosts may live in perpetually lightly-shaded environments, except for periods when deciduous trees lose leaves. Most eventually transition to the adult phase but do not develop large-diameter stems even though they may be a few decades old [135].

Once English ivy begins to ascend a tree, its photosynthetic capacity increases due to increased light, which facilitates a transition to the adult growth phase. In a riparian forest in France, Schnitzler and Heuze [136] observed that the transition took place when vines were about 49 to 70 feet (15-20 m) tall. Under experimental conditions, net photosynthesis was higher in adult than juvenile leaves at low and high light levels [62]. English ivy's net photosynthesis may vary under changing light regimes (see Shade tolerance).

Adult English ivy flowers in bright light [97]. Adult English ivy growing in light shade may produce fruit but in limited quantities [135].

One review from the United Kingdom suggested that English ivy grows most "vigorously" in shaded, moist sites on heavy, fertile soils [97]. However, on Potomac Island in Washington, DC, English ivy's biomass increased with increased light in upland sites. Light, however, was less a factor for growth on newly invaded sites [170]. A study from the Pacific Northwest indicated that English ivy grows throughout the year, although growth may slow or stop during extended drought or periods of intense cold [146]. Growth may slow once English ivy transitions to the adult phase [126]. In experimental plots, English ivy's average total dry shoot weight was higher for plants grown in 60% shade (19.6 g) than for plants grown in full sun (3.3 g) [150]. Researchers from France attributed a reduction in English ivy radial growth to either flood elimination or aging of the plant [65]. Cultivars may have variable growth rates [89].

English ivy does not typically spread to another support if its original host (e.g., tree, shrub) is uprooted or seriously damaged [135,136]. In France, English ivy did not spread to another host tree after the original host tree was uprooted, but it was able to survive another 17 years by developing adventitious roots [135].

SITE CHARACTERISTICS:
Climate: In North America and Europe, English ivy occurs in climates of moderate to high annual precipitation ranging from 20 to 100 inches (see table). In western Oregon, presence of English ivy was negatively correlated (R² = -0.64) with summer precipitation [50].

In the Pacific Northwest—where English ivy is most abundant (see General Distribution)—the climate is maritime, characterized by moderate, wet winters and cool, dry summers. Two localized examples from the Pacific Northwest indicate that English ivy occurs in areas with a mean January temperature of approximately 40 °F (4 °C) [105,174] and a mean August temperature of 59 °F (15 °C) [174].

In northeastern and mid-Atlantic states, English ivy has been found in areas with average minimum temperature ranging from 44 °F (6.6 °C) [162] to 47 °F (8.6 °C) [114,116] and average maximum temperatures ranging from 68.4 °F (20.2 °C) [116] to 69.8 °F (21.0 °C) [114,162]. English ivy occurs in several National Parks in the east with reported mean January temperatures ranging from 24 °F (-4.3 °C) [116] to 32 °F (0 °C) [114,162,197], suggesting that some North American populations of English ivy may be able to tolerate moderately cold winter temperatures. The North American Plant Conservation Alliance considers English ivy cold hardy [160].

In the Southeast, where English ivy is not as common as in other parts of North America (see General Distribution), climates are humid [148] and characterized by warm summers and mild winters [173]. English ivy occurred in the Chauga River Gorge in South Carolina, where midsummer and midwinter temperatures averaged approximately 97 °F (36 °C) and 6.8 °F (-14 °C), respectively [173].

In Europe, English ivy is classified as a southern-temperate species; these are species that are likely to occur in either temperate or Mediterranean climates [118]. It normally develops and fruits where the average temperature in the warmest month is about 55.4 °F (13 °C) but not in areas where the average temperature for the coldest month is 29 °F (-1.5 °C) or less [97]. English ivy is susceptible to low winter temperatures (Godwin 1975 cited in [52]) but may adapt to low winter temperatures by decreasing its metabolic activities  [42]. Based on its elevational range in the Alps (up to about 4,100 feet (1,250 m)), it has been speculated that English ivy's distribution is determined by its limited tolerance to frost. Its northern and eastern distributional limits coincide closely with the -13 °F (-25 °C) minimum-isotherm. At its latitudinal and longitudinal limits, English ivy retains its juvenile form and may be killed by severe frost at -7.6 °F (-22 °C) or less. The adult form of English ivy may be more cold tolerant than the juvenile form [3].

Low temperatures may prevent English ivy from dominating forests in its native range. In northern areas of its native range, temperatures may be low enough to limit photosynthesis and subsequent growth. English ivy’s net photosynthesis increases with warm temperatures [97]. In climates like those of Romania, English ivy stops photosynthesizing for 2 months/yr (Atanasiu 1965 cited in [170]). Seed production may also be limited in cold climates (see Seed production).

Elevation and aspect: English ivy is not common at high elevations. In California, English ivy occurs from sea level to about 3,300 feet (1,000 m) [104,126]. In western Oregon, English ivy became less frequent with increasing elevation [50]. A flora from Utah indicates English ivy occurs at low elevations in that state [192]. In Virginia and North Carolina, English ivy occurs in several National Parks that occur from 49 feet (15 m) [162] to 869 feet (265 m) [116,194] in elevation. In the United Kingdom, English ivy is infrequent at high elevations [145]. Publications from English ivy’s European native range report elevations for English ivy ranging from 300 feet (80 m) (Macleod 1983 cited in [145]) to 2,020 feet (615 m) [52,79,97]. In the Alps, English ivy seldom surpasses 4,100 feet (1,250 m) in elevation [3].

One report from the United Kingdom indicated that English ivy may be slightly more frequent and abundant on north-facing slopes than on other aspects [52].

General habitat: In North America, English ivy commonly occurs in deciduous forest and occasionally in conifer forest ([194], Waggy 2000 personal observation [185]), particularly in the Pacific Northwest (Waggy 2000 personal observation [185]). English ivy occurs in both riparian [86,93,94,119,128,147,157,170] and upland forests and woodlands ([125,137,170], Waggy 2000 personal observation [185]), on forest edges [154,190], roadsides [154], and rocky sites [83,190]. In California, English ivy occurs in wetlands [35] and in valley grasslands and foothill oak woodlands [137]. In the mid-Atlantic states, it occurs in coastal areas, salt marsh edges, and fields in addition to other habitats listed above [159]. Its occurrence is often associated with natural or anthropogenic disturbance [43,104,127,130,160,169,170,197,198], buildings and gardens [30,93,143,170,184,192,197], and urban forests ([50,86,170,183], Waggy 2000 personal observation [185]). Researchers studied the effects of logging on 10 sites in 9 coastal redwood riparian forests in California. Time since last harvest ranged from 10 years to over 100. English ivy was more common on sites logged relatively recently compared to sites that had been logged decades ago [130].

Moisture: In North America, English ivy tolerates a wide range of moisture regimes, from uplands ([125,170], Waggy 2000 personal observation [185]) to floodplains [58,86,169,170,187]. In the mediterranean climate region of California, English ivy was classified as flood tolerant. In this region, English ivy may withstand flooding for most of one growing season and may produce limited root development when flooded [187]. In another study in California, one English ivy plant survived 37 days of flooding at water up to 0.5 foot (0.2 m) deep [58]. In Washington, DC, "excessive" moisture in the root zone did not appear to limit the spread of English ivy in flat portions of a floodplain [169], but on another site in Washington, DC, English ivy's growth in the moist floodplain was slower than on upland sites [170]. Little has been reported on English ivy's tolerance to drought in North American populations, but in Arizona, English ivy was recommended for landscaping based on its low evapotranspiration rate (Pittenger 1990, 1992 cited in [39]).

A literature review from the United Kingdom states that English ivy is tolerant of all but the most water-logged or very dry soils and is favored by moist soils ranging from fairly dry to slightly damp [52,97], although short periods of flooding may favor English ivy germination. In France, the mean stem density of English ivy was significantly (P<0.05) higher on an unflooded site (61.9/ha) compared to a site that received periodic flooding (29.4/ha) [136]. In a fen in England, English ivy was rare on sites saturated for 227 days/year, uncommon (5% of the total dry weight of the vegetation) on sites saturated for 54 days, and dominated sites (77% of the total dry weight of the vegetation) that were saturated for 13 days [73]. Because the relative growth rate for potted English ivy seedlings was not significantly reduced when water was limited, researchers concluded that English ivy was tolerant of drought. Others have described English ivy as a xerophyte (Mittmeyer 1931 cited in [170]). English ivy persists through months of drought in the understories of deeply shaded evergreen forest in the Mediterranean Basin [131,132]. Researchers speculated that English ivy may be favored in the Mediterranean Basin over other woodland species if climates become drier [132]. English ivy may not be as drought tolerant in all parts of the Mediterranean, and summer drought may influence its distribution in that region of the world (Huntley and Birks 1983 cited in [97]).

Substrate: English ivy occurs on a variety of soil types and textures in North America [146,151] and Europe [133,145,188,189]. In the Willamette Valley in Oregon, English ivy occurred in a conifer-deciduous mixed forest in silt loam [66]. In the United Kingdom, it may be abundant on heavy clay soils in low-lying areas [145]. In France, English ivy grows best in sandy soils (Beekman 1984 cited in [135]). In Spain, English ivy seedlings grew on 2 sites in mixed sand, clay, and silt. One site was nearly 50% clay, while the other site was a near-even mixture of the 3 soil textures [133]. In England [38] and the Czech Republic [63], English ivy occurs on limestone and in England [188] and France [135], it occurs on calcareous soil.

One report indicates that English ivy grows well in both acid and basic soils in North America [126]. A Plant Conservation Alliance [160] fact sheet suggests it prefers slightly acid soil (pH 6). A publication recommending species for highway planting in Nevada suggests that English ivy tolerates alkaline and saline soils [151]. In the United Kingdom, English ivy is tolerant of all but extremely acid soil, seldom occurring at pH below 4.0 [52,97], and may be most frequent in soils with pH above 6.0 [52]. In southern England, English ivy occurred on a site with pH of 5.24 or less [102] and in southern Spain, English ivy seedlings occurred in soils with pH of 6.5 and 7.2 [133].

English ivy's photosynthetic capacity adjusts for variable light levels; to what degree may be determined by the life phase (juvenile or adult) of the plant [10,62,110]. In general, adult leaves have a greater photosynthetic capacity than juvenile leaves, even on the same plant [62,97]. Under experimental conditions, juvenile English ivy's capacity to accumulate light was not as well developed as its adult phase. Juvenile leaves, however, tolerated light and were not damaged by increased light [62]. English Ivy may respond quickly to changes in light level by temporarily increasing or decreasing photosynthetic rates. English ivy growing in the shade may undergo brief periods of photoinhibition in the winter when leaves of deciduous trees are shed. For English ivy growing in constant light, photoinhibition may be facilitated by low temperatures [110]. Grime [51] speculated that for juvenile English ivy growing in the shade, carbohydrate availability may depend more on energy conservation than accumulation efficiency.

In some locations, English ivy may reach its greatest abundance in shade. In France, English ivy reached its highest frequency in a floodplain forest on "dark" plots with less than 2.5% light transmission [142]. In experimental plots, English ivy cover grown in 60% shade ranged from about 10% to 70% during a 1-year period. During that same time, English ivy cover failed to reach 20% during any time of the year for plants grown in full sun [150].

Potential successional stage: English ivy's tolerance to a wide range of light levels suggests it may establish and/or persist throughout most successional stages. Information pertaining to English ivy's successional role in its North American range is limited. In forests that had been previously clearcut in western Oregon, English ivy was not present in seedling or sapling stands but occurred in mature stands (frequency <2%; cover ~2%) with large-diameter trees. Thinning mature stands had little effect on English ivy frequency (<1%) compared to unthinned stands (<1%), however, its cover was less in thinned stands (1.5%) than in unthinned stands (3.5%). English ivy frequency generally increased with increased tree canopy cover [50]. In Washington, DC, English ivy occurred in a deciduous forest that had not been logged for 102 years [43]. In a secondary piedmont forest in Georgia, English ivy persisted for at least 30 years (Carter personal communication cited in [11]). In a forest along the Bronx River Parkway in New York, it persisted for at least 25 years [44]. In another secondary piedmont forest in Washington, DC, English ivy displaced the groundlayer vegetation, previously dominated by Virginia springbeauty (Claytonia virginica), within 10 years of its establishment [170].

Several studies and publications from Europe describe English ivy's successional role in parts of its native range [38,56,76,121,135,168]. One long-term study from the United Kingdom indicates that English ivy's successional role may be highly variable. Researchers observed successional changes over 100 years in 2 secondary woodlands where English ivy occurred. The woodlands established on previously cultivated land that had been abandoned for about 20 years. Site 1 consisted of woodland and meadow plant communities and was first surveyed in 1886. English ivy was first observed in the woodland community on Site 1 in 1903. Over the next 53 years English ivy continued to spread, and by 1998 it formed a "dense carpet" in the woodland. In the meadow portion of Site 1, English ivy established in 1913 but was absent by 1945. While it was present during the 1951 and 1965 surveys, it was once again absent from the meadow in 1998. On Site 2, which was primarily a grassland with a few woody species, English ivy was not observed there until 1957, approximately 60 years after surveying began. While it persisted on Site 2 throughout the remainder of the study (1998), it did not dominate [56].

Other studies from Europe indicate that English ivy occurs in early to midsuccession; however, its abundance at any given stage may vary [38,76,121,135,168]. In England, English ivy is typically uncommon in woods except around edges. It establishes during the early stages of succession and may persist for centuries [38,121]. In a previously cultivated hay meadow in England that had been abandoned for 20 to 30 years, English ivy established during the "building phase" (average plant age 15-50 years) of plant community development [76]. In the Chiltern Hills in England, English ivy occurs in various stages of succession, but it is more frequent in early stages of oak woodland succession and in developing woodland [189]. In an oak forest in France, English ivy's frequency increased by 10% within 19 years [168]. In the United Kingdom, English ivy established in a field about 15 years after cultivation ceased and dominated the ground flora of a secondary woodland within 50 years [56]. Because English ivy seedlings establish and grow in both sun and shade (see Shade tolerance), it seems able to establish during early to midstages of succession.

FIRE EFFECTS AND MANAGEMENT

• FIRE EFFECTS
• FUELS AND FIRE REGIMES
• FIRE MANAGEMENT CONSIDERATIONS

Immediate fire effect on plant: As of this writing (2010), information pertaining to the immediate fire effects on English ivy was limited. One literature review indicated English ivy may have low tolerance to fire [97]. Based on its ability to sprout when cut [25,159], English ivy may sprout from fire-damaged stumps; however, its root system may be too shallow to survive surface fire (see Botanical Description). Because English ivy seed is short-lived (see Seed banking), there may be little opportunity for postfire germination from the seed bank. Researchers in Spain found no evidence of rapid postfire establishment of English ivy from the seed bank [181].

Postfire regeneration strategy (adapted from [155]):
Prostrate woody plant, stem growing in organic soil
Surface rhizome and/or a chamaephytic root crown in organic soil or on soil surface
Liana, adventitious buds and/or a sprouting root crown
Initial off-site colonizer (off site, initial community)
Secondary colonizer (on- or off-site seed sources)

Fire adaptations and plant response to fire:

Because English ivy sprouts when cut and roots from stem fragments (see Vegetative regeneration), it may do so if aboveground vines are damaged or killed by fire.

English ivy does not form a persistent seed bank (see Seed banking). Researchers in Spain studied the postfire recruitment of several woody species from the soil seed bank. Based on English ivy's postfire germination rate and its response to experimental smoke and heat treatments, researchers inferred that English ivy seed is not protected from the heat of fire (e.g., lacks hardcoated seed) [181]. Conversely, one invasive species publication indicated that English ivy has a hard seedcoat [126] but provided no evidence in support of this claim.

Inferences based on English ivy's morphology and regeneration suggest some ways in which fire could favor its spread. There is potential for English ivy to establish after fire from off-site seed if there are populations of fruiting English ivy nearby. English ivy seed may be dispersed to burned sites by birds; however, the farther away the source the less likely dispersal is to occur, especially if the source is greater than 3,000 feet (1,000 m) away (see Seed dispersal). A literature review from Great Britain indicated that English ivy seedlings establish on disturbed or open sites [97], suggesting that fire could create conditions favorable for its establishment. However, it may not establish well on sites that experience frequent fire (see Plant response to fire and Fire regimes). English ivy seedlings grow more rapidly on open sites than in shade (see Shade tolerance), suggesting that canopy openings resulting from fire could facilitate rapid growth of English ivy seedlings if they establish on burned sites.

Plant response to fire: Based on its abilities to regenerate vegetatively, adjust to variable light levels, establish on open disturbed sites, and disperse seed over a large area, English ivy may respond favorably to fire. However, the limited available evidence suggests otherwise.

One paleoecological study suggests English ivy may not be favored by fire. Researchers in Switzerland reconstructed historic fire records based on a charcoal and pollen analysis of 2 lakes. Peaks in charcoal particle abundance—presumed to be associated with fire events—were significantly correlated (P=0.05) with repeated declines in the abundance of English ivy pollen [172].

In southern Switzerland, researchers studied historic fire records to evaluate the effects of increasing fire frequency on vegetation. English ivy frequency was greatest on sites with average fire-return intervals of >100 years, declined for sites with average fire-return intervals from 25 to 100 years, and was nearly absent from sites with average fire-return intervals of <25 years. English ivy's frequency generally increased with increasing time since the last fire [28], suggesting that fire exclusion may favor its spread.

• Fuels
• Fire regimes

Because English ivy is evergreen and has a relatively high water content (230 g of water/100 g dry leaf mass (65-70% wet mass)), it may not readily ignite and may burn slowly. Planting English ivy has been recommended to reduce fire risk in seasonally dry areas such as in Utah [80,97], and in chaparral-urban interfaces in California [123].

While dense populations of English ivy clearly affect the structure of surface and crown fuels (see Stand structure), their impact on fire behavior has not been documented. Researchers in the northeastern United States speculated that English ivy may contribute to ladder fuels [29]. A state forester in Delaware also suggested English ivy contributes to ladder fuels and considered it a serious fire hazard near urban communities [166]. Conversely, an ecologist in Portland, Oregon, speculated that English ivy does not contribute to ladder fuels because of its high moisture content. One researcher in that area attempted to burn English ivy that was growing on cliffs with various grasses. The grasses burned but the English ivy did not, presumably because it was "too green" (personal communication [40]). It has been speculated that English ivy may increase fuel loading and continuity by growing up and over supporting vines, shrubs, and trees and by killing the vegetation beneath it [29].

Fire regimes: In its nonnative range in North America, English ivy occurs in plant communities with variable fire regimes, but at the time of this writing (2010), no information was available on how it responds to or influences fire regimes in these communities. Land managers in the Pacific Northwest speculated that English ivy may influence riparian fire regimes; however, the magnitude and direction of its effects on fuel characteristics and fire regimes is unknown. In moist forests where English ivy occurs, extreme fire weather may be a more important driving force of fire intensity and severity than fuel characteristics [1]; therefore, even if English ivy causes marked changes in fuel characteristics, it may have little or no influence on local fire regimes [4].

Studies from Europe indicate that English ivy occurs in communities with variable fire frequency. On the Iberian Peninsula in Spain, English ivy is associated with plant communities occurring in warm, dry Mediterranean climates that are subject to high fire frequency and montane vegetation in subhumid climates where fires are rare [181]. In southern Switzerland, English ivy occurred in forest types that had mean fire-return intervals ranging from 7 to more than 100 years, but its frequency was generally lower in areas with greater fire frequency (see Plant response to fire).

See the Fire Regime Table for further information on fire regimes of vegetation communities in which English ivy may occur. 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".

• Incorporate cost of weed prevention and management into fire rehabilitation plans
• Acquire restoration funding
• Include weed prevention education in fire training
• Minimize soil disturbance and vegetation removal during fire suppression and rehabilitation activities
• Minimize the use of retardants that may alter soil nutrient availability, such as those containing nitrogen and phosphorus
• Avoid areas dominated by high priority invasive plants when locating firelines, monitoring camps, staging areas, and helibases
• Clean equipment and vehicles prior to entering burned areas
• Regulate or prevent human and livestock entry into burned areas until desirable site vegetation has recovered sufficiently to resist invasion by undesirable vegetation
• Monitor burned areas and areas of significant disturbance or traffic from management activity
• Detect weeds early and eradicate before vegetative spread and/or seed dispersal
• Eradicate small patches and contain or control large infestations within or adjacent to the burned area
• Reestablish vegetation on bare ground as soon as possible
• Avoid use of fertilizers in postfire rehabilitation and restoration
• Use only certified weed-free seed mixes when revegetation is necessary

Use of prescribed fire as a control agent: As of this writing (2010), no information was available on the use of prescribed fire to control English ivy. Several invasive species publications indicated that repeat burning with a blowtorch at regular intervals has had some success in controlling English ivy; however, no examples using this method were described [25,125,190]. Although blowtorching may not directly kill English ivy, it may deplete its energy reserves by causing it to continually sprout, which may eventually kill it [125]. Reichard [125] cautioned that this approach requires considerable care. This approach also seems infeasible for large populations of English ivy.

MANAGEMENT CONSIDERATIONS

• FEDERAL LEGAL STATUS
• OTHER STATUS
• IMPORTANCE TO WILDLIFE AND LIVESTOCK
• OTHER USES
• IMPACTS AND CONTROL

In various parts of its European range, English ivy fruit is eaten by numerous native birds including blackcap, European robin, thrushes, and European starling [14,145]. Wood pigeons are the only know predator of English ivy seed [145]. English ivy foliage is subject to extremely low rates of herbivory in Great Britain [52]. In Denmark, farm animals including cattle, domestic sheep, geese, and peafowl eat the juvenile form of English ivy [14].

Palatability and/or nutritional value: English ivy berries are mildly toxic if overconsumed [8,78,99,145,160]. If ingested, English ivy leaves and berries may cause gastrointestinal upset, diarrhea, hyperactivity, breathing difficulty, coma, fever, dilated pupils, muscular weakness, and lack of coordination [160]. English ivy contains allergens that may affect humans [70].

In Britain, English ivy has one of the most nutritious fruits available to birds. Its fruit contains an especially high fat content [145].

Cover value: In Great Britain, English ivy provides excellent cover for some early-nesting birds [52].

Historically, English ivy was used as a topical agent for its antifungal and antimicrobial properties [70].

NatureServe [107] has given English ivy a ranking of medium for its ecological impacts; its impacts to community structure are of greatest concern. The Plant Conservation Alliance [160] considers English ivy a "vigorous" vine that may impact all strata of a forest. In general, English ivy primarily impacts ecological communities by displacing native ground flora, weakening and/or killing host trees and providing opportunity for invasion by other nonnative species [160].

In locations where it is most invasive, English ivy may form near monocultures in the understory [106,160] and suppress growth of ground flora [4,18,24,26,106,146,170]. On Potomac Island in Washington, DC, English ivy suppressed herbs and may have suppressed woody species on upland sites. Because upland sites are not subject to flooding, Thomas [170] speculated that English ivy's impacts may be greater on upland than riparian sites. Thomas further speculated that English ivy's ability to photosynthesize year-round may improve its capacity to suppress the growth of other plants that photosynthesize seasonally [170]. As it spreads, English ivy may eventually displace [140] or inhibit the regeneration of native species [125,190]. Increased shade produced by English ivy may make it difficult for native species to establish in the understory [26]. Because English ivy displaces native plants, wildlife that utilize native plants for forage or cover may also be impacted.

Trees hosting English ivy may be susceptible to windfall during storms [97,125,136,146,160] especially if they are weak [97] or when they are supporting several English ivy stems [136]. Reichard [126] speculated that the additional weight of water or ice on the evergreen leaves of English ivy may increase storm damage to trees. Invasive plant publications suggested that English ivy decreases "vigor" in host trees [99,146], and a study from Oklahoma suggests that English ivy may inhibit development of top and root mass of host trees, particularly maples [141]. Anecdotal information suggests that as English ivy climbs, it covers and kills supporting tree branches by blocking sunlight. The host tree may eventually die from steady weakening [160,170]. American elm trees may be particularly susceptible to weakening by English ivy. In a riparian forest in Washington, DC, 13% of fallen American elm trees had supported English ivy, whereas only 9% of all the other fallen trees species supported English ivy [170].

In a North Carolina riparian forest, English ivy was associated with several other exotic species, and its occurrence was negatively correlated with native species richness (r²= -0.42). Researchers speculate that only the most "aggressive species" were able to coexist with English ivy and that English ivy's presence may promote invasion by other nonnative species because it spreads fast and displaces most native species [183].

Several other ecological impacts of English ivy invasion have been described in the literature, although most have not been well documented. One report from the Pacific Northwest suggested that English ivy may decrease water quality and increase erosion. Researchers have identified English ivy as a host for bacterial leaf scorch (Xylella fastidiosa), a plant pathogen that harms native trees including elms, oaks, and maples [95]. There is some concern that leaf litter from English ivy increases soil nitrogen, which may negatively impact native plant species that grow best in low nutrient conditions (Tremolieres and others 1988 cited in [126]). Based on stream surveys in California, North Dakota, and South Dakota, microinvertebrate frequency was reduced on sites where English ivy occurred in the riparian vegetation compared to sites where it did not occur; however, the difference was not significant [127].

Invasion by English ivy may have societal impacts as well. Trees susceptible to windfall may create a hazard if near roads, walkways, homes, or other developed areas [160]. Loss of shade trees, increased erosion, decreased water quality, and a loss of forest production due to the invasion of English ivy may be costly for public agencies as well as private land owners [146]. In Mediterranean Italy, English ivy growing on old buildings was detrimental to the preservation of an archaeological site [21].

Control: Control of English ivy has received little attention or research. Past research has focused on establishing new cultivars rather than controlling or eliminating the plant [126]. Complicating matters, English ivy continues to be sold at nurseries for landscaping [32,57,150,159], and the American Ivy Society promotes its use in gardens [165].

Fire: For information on the use of prescribed fire to control this species, see Fire Management Considerations.

Prevention: It is commonly argued that the most cost-efficient and effective method of managing invasive species is to prevent their establishment and spread by maintaining "healthy" native communities [91,139] (e.g., avoid road building in wildlands [175]) and by monitoring several times each year [69]. Managing to maintain the integrity of the native plant community and mitigate the factors enhancing ecosystem invasibility is likely to be more effective than managing solely to control the invader [61].

English ivy's escape from cultivation may be slowed or prevented if native species are substituted in landscaping projects. In an attempt to slow English ivy's spread in Oregon, officials have placed English ivy on the list of quarantined species, making it illegal to propagate, transport, purchase, or sell English ivy in that state [113]. It has been suggested that the best way to prevent English ivy invasion is to avoid growing it near forests [25]; however, since its seeds are dispersed by birds (see Seed dispersal), this may not prevent its invasion entirely. One study from the Netherlands suggests that the frequency of English ivy may decrease with increasing size of "woodlot" perimeter [180], so limiting forest fragmentation may reduce English ivy invasion. Thomas [169] suggested that anthropogenic ground disturbance that alters topographic relief may promote invasion by English ivy and other nonnative species and recommended that original topography be restored to sites to preclude or slow English ivy's spread.

Weed prevention and control can be incorporated into many types of management plans, including those for logging and site preparation, grazing allotments, recreation management, research projects, road building and maintenance, and fire management [178]. See the Guide to noxious weed prevention practices [178] for specific guidelines in preventing the spread of weed seeds and propagules under different management conditions.

Cultural control: See Integrated management.

Physical or mechanical control: Several invasive species publications recommend hand removal to control English ivy. Vines may be cut and then pulled down from trees and off the forest floor [25,125,159,190]. Alternatively, English ivy may be pulled up from its roots; however, this method may disturb soil and promote erosion or compaction of the soil [13]. Soil disturbance may facilitate reinvasion by English ivy and/or the establishment of other invasive plants [25,126]. It may be necessary to follow hand removal with additional types of treatments (see Integrated management). Soll [146] cautions that hand removal of English ivy may be costly. In the Pacific Northwest, 2002 cost estimates ranged from $2,000 to $8,000 per acre when paying minimum wage [146].

Researchers in the United Kingdom suggested early thinning of English ivy to help prevent monocultures from forming [56].

Biological control: There are no biological control agents for English ivy. Because English ivy is an important landscape plant and has strong support from the horticultural community, it is extremely unlikely that one will be developed [146]. A study from Oregon evaluated the use of domestic goat browsing to control English ivy in a mixed-deciduous forest where English ivy formed a near monoculture in the groundlayer vegetation. English ivy's average cover declined significantly (P=0.0002) in plots that were browsed by domestic goats compared to unbrowsed plots. Average cover of English ivy was reduced to 23% on sites browsed for 1 year and to 4% on plots browsed for 2 years [66]. In the Netherlands, English ivy invaded a forest and began to climb trees soon after domestic sheep browsing was discontinued [14].

Chemical control: Information pertaining to the chemical control of English ivy is inconsistent. An invasive species report indicated that at best, chemicals offer incomplete control of English ivy [146]. English ivy may be tolerant of preemergent herbicides (Derr 1993 cited in [126]), and its waxy leaves make effective application of postemergent herbicide difficult [190] even when a surfactant is added [126]. Researchers in Portland, Oregon, suggest the under some circumstances, herbicides may provide safe and effective control of English ivy, even during the winter. English ivy's response to chemical control may be influenced by the type of herbicide used, herbicide concentration, and application timing. Herbicide may be most effective when used as a part of an integrated management plan.

Researchers evaluating various chemicals for English ivy control have obtained variable results [13,97,109,161]. For information on using herbicides to control English ivy, see these publications [13,25,109,146,161].

Integrated management: If hand removal is used, follow-up with other types of treatments may improve control. Sprouts from the stumps of cut vines may be treated with herbicide [25,159] or cut repeatedly until sprouting stops [159]. A follow-up planting with native species may help prevent other undesirable plants from becoming established [13,125].

APPENDIX: FIRE REGIME TABLE

REFERENCES

1. Agee, James K. 1997. The severe weather wildfire--too hot to handle? Northwest Science. 71(1): 153-156. [27553]

2. Alabama Invasive Plant Council. 2007. List of Alabama's invasive plants by land-use and water-use sectors. Alabama Invasive Plant Council (Producer). Available: http://www.se-eppc.org/alabama/2007plantlist.pdf [2009, January 5]. [72714]

3. Andergassen, Sigrid; Bauer, Helmut. 2002. Frost hardiness in the juvenile and adult life phase of ivy (Hedera helix L.). Plant Ecology. 161(2): 207-213. [78759]

4. Anzinger, Dawn; Radosevich, Steven R. 2008. Fire and nonnative invasive plants in the Northwest Coastal bioregion. In: Zouhar, Kristin; Smith, Jane Kapler; Sutherland, Steve; Brooks, Matthew L., eds. Wildland fire in ecosystems: fire and nonnative invasive plants. Gen. Tech. Rep. RMRS-GTR-42-vol. 6. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 197-224. [70906]

5. Aphalo, Pedro J.; Sanchez, Rodolfo A. 1986. Stomatal responses to light and drought stress in variegated leaves of Hedera helix. Plant Physiology. 81(3): 768-773. [78777]

6. Asher, Jerry; Dewey, Steven; Olivarez, Jim; Johnson, Curt. 1998. Minimizing weed spread following wildland fires. Proceedings, Western Society of Weed Science. 51: 49. Abstract. [40409]

7. Badre, Bouchra; Nobelis, Photis; Tremolieres, Michele. 1998. Quantitative study and modelling of the litter decomposition in a European alluvial forest. Is there an influence of overstorey tree species on the decomposition of ivy litter (Hedera helix L.)? Acta Oecologica. 19(6): 491-500. [78763]

8. Barnea, Anat; Harborne, Jeffrey B.; Pannell, C. 1993. What part of fleshy fruits contain secondary components toxic to birds and why? Biochemical Systematics and Ecology. 21(4): 421-429. [79753]

9. Baskin, Carol C.; Baskin, Jerry M. 2001. Seeds: ecology, biogeography, and evolution of dormancy and germination. San Diego, CA: Academic Press. 666 p. [60775]

10. Bauer, Helmut; Thoni, Wolfgang. 1988. Photosynthetic light acclimation in fully-developed leaves of the juvenile and adult life phases of Hedera helix. Physiologia Plantarum. 73(1): 31-37. [78773]

11. Biggerstaff, Matthew S.; Beck, Christopher W. 2007. Effects of method of English ivy removal and seed addition on regeneration of vegetation in a southeastern Piedmont forest. The American Midland Naturalist. 158(1): 206-220. [67890]

12. Biggerstaff, Matthew S.; Beck, Christopher. 2007. Effects of English ivy (Hedera helix) on seed bank formation and germination. The American Midland Naturalist. 157(2): 250-257. [70399]

13. Biggerstaff, Matthew; Beck, Christopher. 2002. Effects of English ivy (Hedera helix L.) and differences in its removal on regeneration of native vegetation in a southeastern piedmont forest, [Online]. In: SURE (Summer Undergraduate Research Program at Emory): Past programs--Web posters from SURE 2002. Atlanta, GA: Emory University, ScienceNET (Producer). Available: http://www.cse.emory.edu/sciencenet/undergrad/SURE/Posters/2002_biggerstaff.html [2010, May 25]. [79713]

14. Bottema, S. 2001. A note on the pollen representation of ivy (Hedera helix L.). Review of Palaeobotany and Palynology. 117(1-3): 159-166. [78760]

15. Brooks, Matthew L. 2008. Effects of fire suppression and postfire management activities on plant invasions. In: Zouhar, Kristin; Smith, Jane Kapler; Sutherland, Steve; Brooks, Matthew L., eds. Wildland fire in ecosystems: Fire and nonnative invasive plants. Gen. Tech. Rep. RMRS-GTR-42-vol. 6. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 269-280. [70909]

16. Buckley, G. P.; Howell, R.; Anderson, M. A. 1997. Vegetation succession following ride edge management in lowland plantations and woods. 2. The seed bank resource. Biological Conservation. 82: 305-316. [79690]

17. California Invasive Plant Council. 2006. California invasive plant inventory, [Online]. California Invasive Plant Council (Producer). Available: http://www.cal-ipc.org/ip/inventory/pdf/Inventory2006.pdf [2009, May 6]. [74015]

18. Carey, Andrew B. 2002. Globalization of flora: inviting worldwide ecosystem disaster. Renewable Resources Journal. 20(1): 13-17. [45885]

19. Carter, Gregory A.; Teramura, Alan H. 1988. Vine photosynthesis and relationships to climbing mechanics in a forest understory. American Journal of Botany. 75(7): 1011-1018. [9317]

20. Catling, Paul; Mitrow, Gisele. 2005. A prioritized list of the invasive alien plants of natural habitats in Canada. Canadian Botanical Association Bulletin. 38(4): 55-57. [71460]

21. Celesti-Grapow, Laura; Blasi, Carlo. 2004. The role of alien and native weeds in the deterioration of archaeological remains in Italy. Weed Technology. 18: 1508-1513. [79800]

22. Chaideftou, Evgenia; Thanos, Costas A.; Bergmeier, Erwin; Kallimanis, Athanasios; Dimopoulos, Panayotis. 2009. Seed bank composition and above-ground vegetation in response to grazing in sub-Mediterranean oak forests (NW Greece). Plant Ecology. 201: 255-265. [73402]

23. Clergeau, Philippe. 1992. The effect of birds on seed germination of fleshy-fruited plants in temperate farmland. Acta Oecologica. 13(6): 679-686. [79234]

24. Csurches, S.; Edwards, R. 1998. Potential environmental weeds in Australia: Candidate species for preventative control. Canberra, ACT: Biodiversity Group, Environment Australia. 202 p. Available online: http://www.weeds.gov.au/publications/books/pubs/potential.pdf [2009, January 9]. [72764]

25. Czarapata, Elizabeth J. 2005. Invasive plants of the Upper Midwest: An illustrated guide to their identification and control. Madison, WI: The University of Wisconsin Press. 215 p. [71442]

26. D'Antonio, Carla M.; Haubensak, Karen. 1998. Community and ecosystem impacts of introduced species. Fremontia. 26(4): 13-18. [47114]

27. Debussche, M.; Isenmann, P. 1994. Bird-dispersed seed rain and seedling establishment in patchy Mediterranean vegetation. Oikos. 69(3): 414-426. [79194]

28. Delarze, R.; Caldelari, D.; Hainard, P. 1992. Effects of fire on forest dynamics in southern Switzerland. Journal of Vegetation Science. 3(1): 55-60. [71411]

29. Dibble, Alison C.; Zouhar, Kristin; Smith, Jane Kapler. 2008. Fire and nonnative invasive plants in the Northeast bioregion. In: Zouhar, Kristin; Smith, Jane Kapler; Sutherland, Steve; Brooks, Matthew L., eds. Wildland fire in ecosystems: fire and nonnative invasive plants. Gen. Tech. Rep. RMRS-GTR-42-vol. 6. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 61-90. [70902]

30. Diggs, George M., Jr.; Lipscomb, Barney L.; O'Kennon, Robert J. 1999. Illustrated flora of north-central Texas. Sida Botanical Miscellany, No. 16. Fort Worth, TX: Botanical Research Institute of Texas. 1626 p. [35698]

31. Dirr, Michael A.; Heuser, Charles W., Jr. 1987. The reference manual of woody plant propagation: From seed to tissue culture. Athens, GA: Varsity Press, Inc. 239 p. [16999]

32. Douglas-Smith, Angela. 2006. Control of Ailanthus altissima (Mill.) Swingle, Albizia julibrissin Durazzini, Hedera helix L. and Paulowina tomentosa (Thunb.) Seib & Zucc. Ex Steud. in three Tidewater Virginia area parks. Newport News, VA: Christopher Newport University. 60 p. Thesis. [72016]

33. Dowhan, Joseph J.; Rozsa, Ron. 1989. Flora of Fire Island, Suffolk County, New York. Bulletin of the Torrey Botanical Club. 116(3): 265-282. [22041]

34. Dudley, Tom. 1998. Exotic plant invasions in California riparian areas and wetlands. Fremontia. 26(4): 24-29. [47116]

35. Dudley, Tom; Collins, Beth. 1995. Biological invasions in California wetlands: The impacts and control of non-indigenous species in natural areas. Oakland, CA: Pacific Institute for Studies in Development, Environment, and Security. 59 p. [+ appendices]. [47513]

36. Elliot, C. 1995. The ivy debate. Horticulture. 73(3): 21-23. [79233]

37. Ewers, Frank W.; Fisher, Jack B.; Fichtner, Klaus. 1991. Water flux and xylem structure in vines. In: Putz, Francis E.; Mooney, Harold A., eds. The biology of vines. New York: Cambridge University Press: 127-160. [79283]

38. Faegri, K.; van der Pijl, L. 1979. The principles of pollination ecology. 3rd ed. Oxford, UK: Pergamon Press. 242 p. [79305]

39. Feldman, William R.; Carter, Steven A.; Stone, Kim W. 1997. Water requirements of arid-adapted groundcover and subshrub species for landscape use in Arizona. Desert Plants. 13(1): 18-24. [28501]

40. Felice, Rachel. 2010. [Email to Melissa Waggy]. June 5. Regarding English ivy. Portland, OR: City Nature West. On file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT; FEIS files. [80189]

41. Fierke, Melissa K.; Kauffman, J. Boone. 2006. Invasive species influence riparian plant diversity along a successional gradient, Willamette River, Oregon. Natural Areas Journal. 26(4): 376-382. [65074]

42. Fisher, A.; Feller, U. 1994. Seasonal changes in the pattern of assimilatory enzymes and the proteolytic activities in leaves of juvenile ivy. Annals of Botany. 74: 389-396. [79301]

43. Fleming, Peggy; Kanal, Raclare. 1995. Annotated list of vascular plants of Rock Creek Park, National Park Service, Washington, DC. Castanea. 60(4): 283-316. [71991]

44. Frankel, Edward. 1999. A floristic survey of vascular plants of the Bronx River Parkway Reservation in Westchester, New York: compilation 1973-1998. Journal of the Torrey Botanical Society. 126(4): 359-366. [37376]

45. Georgia Exotic Pest Plant Council. 2006. List of non-native invasive plants in Georgia, [Online]. Southeast Exotic Pest Plant Council (Producer). Available: http://www.gaeppc.org/list.cfm [2009, January 5]. [72787]

46. Gleason, H. A.; Cronquist, A. 1963. Manual of vascular plants of northeastern United States and adjacent Canada. Princeton, NJ: D. Van Nostrand Company, Inc. 810 p. [7065]

47. Goodwin, Kim; Sheley, Roger; Clark, Janet. 2002. Integrated noxious weed management after wildfires. EB-160. Bozeman, MT: Montana State University, Extension Service. 46 p. Available online: http://www.montana.edu/wwwpb/pubs/eb160.html [2003, October 1]. [45303]

48. Grashof-Bokdam, C. J.; Geertsema, W. 1998. The effect of isolation and history on colonization patterns of plant species in secondary woodland. Journal of Biogeography. 25(5): 837-846. [73922]

49. Grasovsky, Amihud. 1929. Some aspects of light in the forest. School of Forestry Bulletin No. 23. New Haven, CT: Yale University. 53 p. [79563]

50. Gray, Andrew N. 2005. Eight nonnative plants in western Oregon forests: associations with environment and management. Environmental Monitoring and Assessment. 100(1-3): 109-127. [63196]

51. Grime, J. P. 1965. Shade tolerance in flowering plants. Nature. 28(5006): 161-163. [46122]

52. Grime, J. P.; Hodgson, J. G.; Hunt, R. 1988. Comparative plant ecology: A functional approach to common British species. Boston: Allen & Unwin. 752 p. [79296]

53. Groffman, Peter M.; Pouyat, Richard V.; Cadenasso, Mary L.; Zipperer, Wayne C.; Szlavecz, Katalin; Yesilonis, Ian D.; Band, Lawrence E.; Brush, Grace S. 2006. Land use context and natural soil controls on plant community composition and soil nitrogen and carbon dynamics in urban and rural forests. Forest Ecology and Management. 236(2-3): 177-192. [72487]

54. Hann, Wendel; Havlina, Doug; Shlisky, Ayn; [and others]. 2008. Interagency fire regime condition class guidebook. Version 1.3, [Online]. In: Interagency fire regime condition class website. U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; The Nature Conservancy; Systems for Environmental Management (Producer). 119 p. Available: http://frames.nbii.gov/frcc/documents/FRCC_Guidebook_2008.07.10.pdf [2010, 3 May]. [70966]

55. Harlow, Richard F.; Urbston, David F.; Williams, James G., Jr. 1979. Forages eaten by deer in two habitats at the Savannah River Plant. Res. Note SE-275. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station. 4 p. [41846]

56. Harmer, Ralph; Peterken, George; Kerr, Gary; Poulton, Paul. 2001. Vegetation changes during 100 years of development of two secondary woodlands on abandoned arable land. Biological Conservation. 101: 291-304. [79678]

57. Harris, Courtney; Jiang, Hao; Liu, Dongjiao; Brian, Zachary; He, Kate. 2009. Testing the roles of species native origin and family membership in intentional plant introductions using nursery data across the state of Kentucky. Journal of the Torrey Botanical Society. 136(1): 122-127. [79204]

58. Harris, Richard W.; Leiser, Andrew T.; Fissell, Robert E. 1975. Plant tolerance to flooding. Summary report -- 1971-1975. Grant Contract No. A 5fs-16565; RWH-200-7/1/75. Davis, CA: University of California, Department of Environmental Horticulture. 30 p. In cooperation with: U.S. Army Corps of Engineers; U.S. Department of Agriculture, Forest Service. [76584]

59. Herrera, Carlos M. 1987. Vertebrate-dispersed plants of the Iberian Peninsula: A study of fruit characteristics. Ecological Monographs. 57(4): 305-331. [74593]

60. Hitchcock, C. Leo; Cronquist, Arthur; Ownbey, Marion; Thompson, J. W. 1961. Vascular plants of the Pacific Northwest. Part 3: Saxifragaceae to Ericaceae. Seattle, WA: University of Washington Press. 614 p. [1167]

61. Hobbs, Richard J.; Humphries, Stella E. 1995. An integrated approach to the ecology and management of plant invasions. Conservation Biology. 9(4): 761-770. [44463]

62. Hoflacher, Hans; Bauer, Helmut. 1982. Light acclimation in leaves of the juvenile and adult life phases of ivy (Hedera helix). Physiolgia Plantarum. 56: 177-82. [79538]

63. Hofmeister, Jenyk; Hosek, Jan; Modry, Martin; Rolecek, Jan. 2009. The influence of light and nutrient availability on herb layer species richness in oak-dominated forests in central Bohemia. Plant Ecology. 205: 57-75. [77027]

64. Hruska, Krunica. 1991. Human impact on the forest vegetation in the western part of the Pannonic Plain (Yugoslavia). Vegetatio. 92: 161-166. [73486]

65. Hueze, Patricia; Dupouey, Jean-Luc; Schnitzler, Annik. 2009. Radial growth response of Hedera helix to hydrological changes and climatic variability in the Rhine floodplain. River Research and Applications. 25(4): 393-404. [78040]

66. Ingham, Claudia S.; Borman, Michael M. 2010. English ivy (Hedera spp., Araliaceae) response to goat browsing. Invasive Plant Science and Management. 3: 178-181. [79900]

67. ITIS Database. 2010. Integrated taxonomic information system, [Online]. Available: http://www.itis.gov/index.html. [51763]

68. Jackson, G.; Sheldon, J. 1949. The vegetation of magnesian limestone cliffs at Markland Grips near Sheffield. The Journal of Ecology. 37(1): 38-50. [72536]

69. Johnson, Douglas E. 1999. Surveying, mapping, and monitoring noxious weeds on rangelands. In: Sheley, Roger L.; Petroff, Janet K., eds. Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press: 19-36. [35707]

70. Jones, J. M.; White, I. R.; White, J. M. L.; McFadden, J. P. 2009. Allergic contact dermatitis to English ivy (Hedera helix)--a case series. Contact Dermatitis. 60(3): 180-180. [78041]

71. Jones, Ronald L. 1983. Woody flora of Shiloh National Military Park, Hardin County, Tennessee. Castanea. 48(4): 289-299. [71737]

72. Kartesz, John T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. 1st ed. In: Kartesz, John T.; Meacham, Christopher A. Synthesis of the North American flora (Windows Version 1.0), [CD-ROM]. Chapel Hill, NC: North Carolina Botanical Garden (Producer). In cooperation with: The Nature Conservancy; U.S. Department of Agriculture, Natural Resources Conservation Service; U.S. Department of the Interior, Fish and Wildlife Service. [36715]

73. Kassas, M. 1952. Studies in the ecology of Chippenham fen. III. The Forty Acre Wood. Journal of Ecology. 40(1): 50-61. [79566]

74. Kentucky Exotic Pest Plant Council. 2008. Invasive exotic plant list, [Online]. Southeast Exotic Pest Plant Council (Producer). Available: http://www.se-eppc.org/ky/list.htm [2009, January 5]. [72785]

75. Kjellson, Gosta. 1992. Seed banks in Danish deciduous forests: species composition, seed influx and distribution pattern in soil. Ecography. 15: 86-100. [74170]

76. Kollmann, Johannes. 1995. Regeneration window for fleshy-fruited plants during scrub development on abandoned grassland. Ecoscience. 2(3): 213-222. [69004]

77. Kollmann, Johannes; Grubb, Peter J. 1999. Recruitment of fleshy-fruited species under different shrub species: control by under-canopy environment. Ecological Research. 14(1): 9-21. [72620]

78. Krochmal, A.; Lavrentiades, G. 1955. Poisonous plants of Greece. Economic Botany. 9(2): 175-189. [71618]

79. Kubicek, Ferdinand; Jurko, Anton. 1975. Estimation of the above-ground biomass of the herb layer in forest communities. Folia Geobotanica & Phytotaxonomica. 10(2): 113-129. [76307]

80. Kuhns, Mike. 2010. Firewise plants for Utah landscapes. Utah Forest Facts--Fact Sheet NR/FF/002. Logan, UT: Utah State University, Forestry Extension. 4 p. Available: http://extension.usu.edu/files/publications/publication/NR_FF_002.pdf [2010, March 26]. [80146]

81. LANDFIRE Rapid Assessment. 2005. Reference condition modeling manual (Version 2.1), [Online]. In: LANDFIRE. Cooperative Agreement 04-CA-11132543-189. Boulder, CO: The Nature Conservancy; U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior (Producers). 72 p. Available: http://www.landfire.gov/downloadfile.php?file=RA_Modeling_Manual_v2_1.pdf [2007, May 24]. [66741]

82. LANDFIRE Rapid Assessment. 2007. Rapid assessment reference condition models, [Online]. In: LANDFIRE. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab; U.S. Geological Survey; The Nature Conservancy (Producers). Available: http://www.landfire.gov/models_EW.php [2008, April 18] [66533]

83. Leck, Mary Allessio; Leck, Charles F. 2005. Vascular plants of a Delaware River tidal freshwater wetland and adjacent terrestrial areas: seed bank and vegetation comparisons of reference and constructed marshes and annotated species list. Journal of the Torrey Botanical Society. 132(2): 323-354. [60627]

84. Lee, David W.; Richards, Jennifer H. 1991. Heteroblastic development in vines. In: Putz, Francis E.; Mooney, Harold A., eds. The biology of vines. New York: Cambridge University Press: 207-244. [79646]

85. Lhotska, Marie. 1974. The after-ripening of embryos on the mother plant. Folia Geobotanica & Phytotaxonomica. 9(3): 231-240. [79217]

86. Loewenstein, Nancy J.; Loewenstein, Edward F. 2005. Non-native plants in the understory of riparian forests across a land use gradient in the Southeast. Urban Ecosystems. 8(1): 79-91. [75882]

87. Lorenz, David G.; Sharp, W. Curtis.; Ruffner, Joseph D. 1991. Conservation plants for the Northeast. Program Aid 1154. [Washington, DC]: U.S. Department of Agriculture, Soil Conservation Service. 43 p. [47719]

88. Luken, James O. 2003. Invasions of forests in the eastern United States. In: Gilliam, Frank S.; Roberts, Mark R., eds. The herbaceous layer in forests of eastern North America. New York: Oxford University Press, Inc: 283-400. [71484]

89. Mack, James A.; Swasey, James E. 1988. Evaluation of selected Hedera helix cultivars. HortScience. 23(3): 801. Abstract. [78770]

90. Mack, Richard N. 1991. The commercial seed trade: an early disperser of weeds in the United States. Economic Botany. 45(2): 257-273. [55368]

91. Mack, Richard N.; Simberloff, Daniel; Lonsdale, W. Mark; Evans, Harry; Clout, Michael; Bazzaz, Fakhri A. 2000. Biotic invasions: causes, epidemiology, global consequences, and control. Ecological Applications. 10(3): 689-710. [48324]

92. Magee, Dennis W.; Ahles, Harry E. 2007. Flora of the Northeast: A manual of the vascular flora of New England and adjacent New York. 2nd ed. Amherst, MA: University of Massachusetts Press. 1214 p. [74293]

93. Marshall, Judy; Balda, Russell P. 1974. The breeding ecology of the painted redstart. The Condor. 76(1): 89-101. [73942]

94. McCain, Cindy; Christy, John A. 2005. Field guide to riparian plant communities in northwestern Oregon. Tech. Pap. R6-NR-ECOL-TP-01-05. [Portland, OR]: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 357 p. [63114]

95. McElrone, Andrew J.; Sherald, James L.; Pooler, Margaret R. 1999. Identification of alternative hosts of Xylella fastidiosa in the Washington, D.C., area using nested polymerase chain reaction (PCR). Journal of Arboriculture. 25(5): 258-263. [49781]

96. Mehrhoff, L. J.; Silander, J. A., Jr.; Leicht, S. A.; Mosher, E. S.; Tabak, N. M. 2003. IPANE: Invasive Plant Atlas of New England, [Online]. Storrs, CT: University of Connecticut, Department of Ecology and Evolutionary Biology (Producer). Available: http://nbii-nin.ciesin.columbia.edu/ipane/ [2008, May 28]. [70356]

97. Metcalfe, Daniel L. 2005. Biological flora of the British Isles: Hedera helix L. Journal of Ecology. 93(3): 632-648. [78757]

98. Michigan Invasive Plant Council. 2008. Summary statement: Hedera helix--English ivy, [Online]. In: Michigan Plant Invasiveness Assessment System--Assessed plants. East Lansing, MI: Michigan Invasive Plant Council (Producer). Available: http://invasiveplantsmi.org/ [2010, June 25]. [80188]

99. Miller, James H. 2003. Nonnative invasive plants of southern forests: A field guide for identification and control. Gen. Tech. Rep. SRS-62. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 93 p. Available online: http://www.srs.fs.usda.gov/pubs/gtr/gtr_srs062/ [2004, December 10]. [50788]

100. Miller, James H.; Chambliss, Erwin B. 2008. Regional maps by acres covered in a county by the NIPS species, [Online]. In: Maps of occupation and estimates of acres covered by nonnative invasive plants in southern forests using SRS FIA data posted on March 15, 2008. Athens, GA: University of Georgia, Bugwood Network; Washington, DC: U.S. Department of Agriculture, Forest Service; Animal and Plant Inspection Service, Plant Protection and Quarantine (Producers). Available: http://www.invasive.org/fiamaps/acres.cfm [2009, October 21]. [76599]

101. Missouri Botanical Garden. 2002. Missouri exotic pest plants: A list of non-native plants that threaten Missouri's native biodiversity, [Online]. In: MO projects--North America. St. Louis, MO: Missouri Botanical Garden (Producer). Available: http://www.mobot.org/mobot/research/mepp/alphalist.shtml [2009, April 6]. [73559]

102. Mitchell, R. J.; Marrs, R. H.; Le Duc, M. G.; Auld, M. H. D. 1997. A study of succession on lowland heaths in Dorset, southern England: changes in vegetation and soil chemical properties. Journal of Applied Ecology. 34(6): 1426-1444. [60997]

103. Mohlenbrock, Robert H. 1986. [Revised edition]. Guide to the vascular flora of Illinois. Carbondale, IL: Southern Illinois University Press. 507 p. [17383]

104. Nakanishi, Hiroki. 1996. Fruit color and fruit size of bird-disseminated plants in Japan. Vegetatio. 123(2): 207-218. [75442]

105. National Oceanic and Atmospheric Administration. 2010. Portland (airport to downtown) precipitation data--Downtown data is 1871 - July 2009, while airport is October 1840 - July 2009, [Online]. In: Local climate data from Portland Airport. Portland, OR: NOAA's National Weather Service (Producer). Available: http://www.wrh.noaa.gov/pqr/pdxclimate/index.php [2010, June 10]. [80205]

106. Native Plant Society of Oregon, Emerald Chapter. 2008. Exotic gardening and landscaping plants invasive in native habitats of the southern Willamette Valley, [Online]. In: Invasive plants--Invasive exotic plants list 2008. Native Plant Society of Oregon (Producer). Available: http://www.emeraldnpso.org/PDFs/Invas_Orn.pdf [2009, June 24]. [74811]

107. NatureServe. 2004. International Ecological Classification Standard: terrestrial ecological classifications--Uwharrie National Forest final report, [Online]. Subset of NatureServe central databases. 89 p. In: Publications--library. Arlington, VA: NatureServe (Producer). Available: http://www.natureserve.org/library/uwharrieNF.pdf [2010, August 20]. [79632]

108. NatureServe. 2010. Comprehensive report: Hedera helix--English ivy, [Online]. In: NatureServe Explorer: An online encyclopedia of life. Version 7.1. Arlington, VA: NatureServe (Producer). Available: http://www.natureserve.org/explorer [2010, August 30]. [80478]

109. Neal, J. C.; Skroch, W. A. 1985. Effects of timing and rate of glyphosate application on toxicity to selected woody ornamentals. Journal of American Society of Horticultural Scientists. 110: 860-864. [79560]

110. Oberhuber, Walter; Bauer, Helmut. 1991. Photoinhibition of photosynthesis under natural conditions in ivy (Hedera helix L.) growing in an understory of deciduous trees. Planta. 185(4): 545-553. [78766]

111. Okerman, Anne. 2000. Combating the "ivy desert": The invasion of Hedera helix (English ivy) in the Pacific Northwest United States, [Online]. In: Restoration and Reclamation Review--Student Online Journal. Volume 6.4--Fall 2000: Invasive species of the forest ground plane. St. Paul, MN: University of Minnesota--Twin Cities, Department of Horticultural Science (Producer). Available: http://purl.umn.edu/59738 [2010, March 23]. [80191]

112. Olano, J. M.; Caballero, I.; Laskurain, N. A.; Loidi, J.; Escudero, A. 2002. Seed bank spatial pattern in a temperate secondary forest. Journal of Vegetation Science. 13(6): 775-778. [79907]

113. Oregon Department of Agriculture. 2010. Noxious weeds quarantine, [Online]. In: Quarantines and control area orders--Noxious weed control. Salem, OR: Oregon Department of Agriculture, Plant Division (Producer). Available: http://egov.oregon.gov/ODA/PLANT/603_052_1200.shtml [2010, June 2]. [80192]

114. Patterson, Karen D. 2008. Vegetation classification and mapping at Colonial National Historical Park, Virginia. Technical Report NPS/NER/NRTR--2008/129. Philadelphia, PA: U.S. Department of the Interior, National Park Service, Northeast Region. 369 p. [79670]

115. Patterson, Karen D. 2008. Vegetation classification and mapping at George Washington Birthplace National Monument, Virginia. Technical Report NPS/NER/NRTR--2008/099. Philadelphia, PA: U.S. Department of the Interior, National Park Service, Northeast Region. 231 p. [79672]

116. Patterson, Karen D. 2008. Vegetation classification and mapping at Petersburg National Battlefield, Virginia. Technical Report NPS/NER/NRTR--2008/127. Philadelphia, PA: U.S. Department of the Interior, National Park Service, Northeast Region. 235 p. [79673]

117. Patterson, Karen D. 2008. Vegetation classification and mapping at Richmond National Battlefield Park, Virginia. Technical Report NPS/NER/NRTR--2008/128. Philadelphia, PA: U.S. Department of the Interior, National Park Service, Northeast Region. 244 p. [79674]

118. Preston, Christopher D.; Hill, Mark O. 1997. The geographical relationships of British and Irish flora. Botanical Journal of the Linnean Society. 124: 1-120. [79977]

119. Pyle, Laura L. 1995. Effects of disturbance on herbaceous exotic plant species on the floodplain of the Potomac River. The American Midland Naturalist. 134: 244-253. [26182]

120. Racine, Charles H.; Hardin, James W. 1975. The vascular flora and vegetation in the Green River Gorge, North Carolina. Castanea. 40(4): 319-345. [72119]

121. Rackham, Oliver. 1990. [Revised edition]. Trees and woodland in the British landscape. London: J. M. Dent & Sons. 256 p. [79278]

122. Radford, Albert E.; Ahles, Harry E.; Bell, C. Ritchie. 1968. Manual of the vascular flora of the Carolinas. Chapel Hill, NC: The University of North Carolina Press. 1183 p. [7606]

123. Radtke, Klaus W. H. 1983. Living more safely in the chaparral-urban interface. Gen. Tech. Rep. PSW-67. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 50 p. [35802]

124. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]

125. Reichard, Sarah. 1996. Hedera helix--English ivy. In: Randall, John M.; Marinelli, Janet, eds. Invasive plants: Weeds of the global garden. Handbook #149. Brooklyn, NY: Brooklyn Botanic Garden: 93. [73462]

126. Reichard, Sarah. 2000. Hedera helix. In: Bossard, Carla C.; Randall, John M.; Hoshovsky, Marc C., eds. Invasive plants of California's wildlands. Berkeley, CA: University of California Press: 212-216. [79542]

127. Ringold, Paul L.; Magee, Teresa K.; Peck, David V. 2008. Twelve invasive plant taxa in US western riparian ecosystems. Journal of the North American Benthological Society. 27(4): 949-966. [73064]

128. Roberts, Warren G.; Howe, J. Greg; Major, Jack. 1980. A survey of riparian forest flora and fauna in California. In: Sands, Anne, ed. Riparian forests in California: Their ecology and conservation: Symposium proceedings; 1977 May 14; Davis, CA. Institute of Ecology Publication No. 15. Davis, CA: University of California, Division of Agricultural Sciences: 3-19. [5271]

129. Rogler, Charles E.; Hackett, Wesley P. 1975. Phase change in Hedera helix: induction of mature to juvenile phase change by gibberellin A3. Physiologia Plantarum. 34: 141-7. [79539]

130. Russell, Will. 2009. The influence of timber harvest on the structure and composition of riparian forests in the coastal redwood region. Forest Ecology and Management. 257(5): 1427-1433. [73792]

131. Sack, Lawren. 2004. Responses of temperate woody seedlings to shade and drought: do trade-offs limit potential niche differentiation? Oikos. 107: 101-127. [79295]

132. Sack, Lawren; Grubb, Peter J. 2002. The combined impacts of deep shade and drought on the growth and biomass allocation of shade-tolerant woody seedlings. Oecologia. 131(2): 175-185. [78830]

133. Sack, Lawren; Grubb, Peter J.; Maranon, Teodoro. 2003. The functional morphology of juvenile plants tolerant of strong summer drought in shaded forest understories in southern Spain. Plant Ecology. 168(1): 139-163. [79227]

134. Sawyer, John O.; Sillett, Stephen C.; Popenoe, James H.; LaBanca, Anthony; Sholars, Teresa; Largent, David L.; Euphrat, Fred; Noss, Reed F.; Van Pelt, Robert. 2000. Characteristics of redwood forests. In: Noss, Reed F., ed. The redwood forest: History, ecology, and conservation of the coast redwoods. Washington, DC: Island Press: 39-79. [40464]

135. Schnitzler, Annik. 1995. Community ecology of arboreal lianas in gallery forests of the Rhine valley, France. Acta Oecologica. 16: 219-236. [79272]

136. Schnitzler, Annik; Heuze, Patricia. 2006. Ivy (Hedera helix L.) dynamics in riverine forests: effects of river regulation and forest disturbance. Forest Ecology and Management. 236(1): 12-17. [78755]

137. Schwartz, Mark W.; Porter, Daniel J.; Randall, John M.; Lyons, Kelly E. 1996. Impact of nonindigenous plants. In: Status of the Sierra Nevada. Sierra Nevada Ecosystem Project: Final report to Congress. Volume II: Assessments and scientific basis for management options. Wildland Resources Center Report No. 37. Davis, CA: University of California, Centers for Water and Wildland Resources: 1203-1218. [28977]

138. Scoggan, H. J. 1978. The flora of Canada. Part 4: Dicotyledoneae (Dictoyledonceae to Compositae). National Museum of Natural Sciences: Publications in Botany, No. 7(4). Ottawa: National Museums of Canada. 1711 p. [78054]

139. Sheley, Roger; Manoukian, Mark; Marks, Gerald. 1999. Preventing noxious weed invasion. In: Sheley, Roger L.; Petroff, Janet K., eds. Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press: 69-72. [35711]

140. Sholars, Teresa; Golec, Clare. 2007. Rare plants of the redwood forest and forest management effects. In: Standiford, Richard B.; Giusti, Gregory A.; Valachovic, Yana; Zielinski, William J.; Furniss, Michale J., tech. eds. Proceedings of the redwood region forest science symposium: What does the future hold; 2004 March 15-17; Rohnert Park, CA. Gen. Tech. Rep. RSW-GTR-194. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 185-199. [71159]

141. Shoup, Steve; Whitcomb, Carl E. 1979. Interactions between trees and ground covers. In: Res. Rep. 791--Report No. 5. [Stillwater, OK]; Oklahoma State University, Agricultural Experiment Station: 56-57. [22579]

142. Siebel, Henk N.; Bouwma, Irene M. 1998. The occurrence of herbs and woody juveniles in a hardwood floodplain forest in relation to flooding and light. Journal of Vegetation Science. 9(5): 623-630. [73525]

143. Simmons, Mark P.; Ware, Donna M. E.; Hayden, W. John. 1995. The vascular flora of the Potomac River watershed of King George County, Virginia. Castanea. 60(3): 179-209. [73734]

144. Slade, Andrew J.; Hutchings, Michael J. 1989. Within- and between-population variation in ramet behaviour in the gynodioecious clonal herb, Glechoma hederacea (Labiatae). Canadian Journal of Botany. 67(3): 633-639. [71829]

145. Snow, Barbara; Snow, David. 1988. Birds and berries: A study of ecological interaction. Staffordshire, UK: T. & A. D. Poyser. 268 p. [74664]

146. Soll, Jonathan. 2005. Controlling English ivy (Hedera helix) in the Pacific Northwest, [Online]. In: Control methods--Invasive plant management. In: GIST (Global Invasive Species Team). Arlington, VA: The Nature Conservancy (Producer). Available: http://www.invasive.org/gist/moredocs/hedhel02.pdf [2010, May 27]. [80194]

147. Soll, Jonathan; Kreuzer, Doug; Dumont, Jason; Matthews, Ian; Hoeh, Merrit. 2008. Sandy River Riparian Habitat Protection Project report 2008. Portland, OR: The Nature Conservancy in Oregon. 50 p. [74016]

148. Sorrie, Bruce A.; Gray, Janet Bracey; Crutchfield, Philip J. 2006. The vascular flora of the longleaf pine ecosystem of Fort Bragg and Weymouth Woods, North Carolina. Castanea. 71(2): 129-161. [71947]

149. Southeast Exotic Pest Plant Council. 2003. Southeast Exotic Pest Plant Council invasive plant manual, [Online]. Southeast Exotic Pest Plant Council (Producer). Available: http://www.invasive.org/eastern/eppc/index.html [2005, August 10]. [54193]

150. Stafne, R. A.; Einert, A. E.; Klingaman, G. L. 2005. Fertilizer applications on establishment and growth of three groundcover species in sun and shade. Journal of Environmental Horticulture. 23(3): 157-161. [71717]

151. Stark, N. 1966. Review of highway planting information appropriate to Nevada. Bulletin No. B-7. Reno, NV: University of Nevada, College of Agriculture, Desert Research Institute. 209 p. In cooperation with: Nevada State Highway Department. [47]

152. Stavretovic, N. 2007. Biological characteristics of the species Hedera helix L. and its use in controlling erosion in shady places. Archives of Biological Sciences. 59(2): 139-143. [78044]

153. Stein, Otto L.; Fosket, Elizabeth B. 1969. Comparative developmental anatomy of shoots of juvenile and adult Hedera helix. American Journal of Botany. 56(5): 546-551. [78795]

154. Steury, Brent W; Davis, Charles A. 2003. The vascular flora of Piscataway and Fort Washington National Parks, Prince Georges and Charles Counties, Maryland. Castanea. 68(4): 271-299. [73054]

155. Stickney, Peter F. 1989. Seral origin of species comprising secondary plant succession in Northern Rocky Mountain forests. FEIS workshop: Postfire regeneration. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 10 p. [20090]

156. Stocker, Randall; Hupp, Karen V. S. 2008. Fire and nonnative invasive plants in the Southeast bioregion. In: Zouhar, Kristin; Smith, Jane Kapler; Sutherland, Steve; Brooks, Matthew L., eds. Wildland fire in ecosystems: fire and nonnative invasive plants. Gen. Tech. Rep. RMRS-GTR-42-vol. 6. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 91-112. [70903]

157. Stromberg, Laurence P.; Katibah, Edwin F. 1984. An application of the spatial-aggregation method to the description of riparian vegetation. In: Warner, Richard E.; Hendrix, Kathleen M., eds. California riparian systems: Ecology, conservation, and productive management: Proceedings of a conference; 1981 September 17-19; Davis, CA. Berkeley, CA: University of California Press: 347-355. [5839]

158. Sulgrove, Sabina Mueller. 1987. Six hardy ground covers from the American Ivy Society. American Nurseryman. 165: 116-129. [79754]

159. Swearingen, J.; Reshetiloff, K.; Slattery, B.; Zwicker, S. 2002. Plant invaders of mid-Atlantic natural areas. [Washington, DC]: U.S. Department of the Interior, National Park Service; Fish and Wildlife Service. 82 p. Available online: http://www.invasive.org/eastern/midatlantic/index.html [2009, November 19]. [54192]

160. Swearingen, Jill M.; Diedrich, Sandra. 2006. Fact sheet: English ivy--Hedera helix L., [Online]. In: Weeds gone wild: Alien plant invaders of natural areas--Fact sheets. Plant Conservation Alliance's Alien Plant Working Group (Producer). Available: http://www.nps.gov/plants/alien/fact/hehe1.htm [2010, June 1]. [80193]

161. Talbert, R. E.; Saunders, P. A.; Wallinder, C. J.; Klingman, G. L. 1980. Evaluation of herbicides in field-grown ornamental crops, 1979. Mimeograph Series 277. Fayetteville, AR: University of Arkansas, Division of Agriculture, Agricultural Experiment Station. 15 p. [73900]

162. Taverna, Kristin. 2008. Vegetation classification and mapping at Fredericksburg and Spotsylvania National Military Park. Technical Report NPS/NER/NRTR--2008/126. Philadelphia, PA: U.S. Department of the Interior, National Park Service, Northeast Region. 277 p. [79671]

163. Tennessee Exotic Pest Plant Council. 2009. Invasive plants of Tennessee, [Online]. In: TN-EPPC invasive exotic pest plants in Tennessee--December 2009, 2nd edition. Fairview, TN: Tennessee Exotic Pest Plant Council (Producer). Available: http://www.tneppc.org/invasive_plants [2010, June 23]. [80199]

164. Terrell, Edward E. 1970. Spring flora of the Chesapeake and Ohio Canal area, Washington, D.C. to Seneca, Maryland. Castanea. 35(1): 1-26. [73736]

165. The American Ivy Society. 2010. Ivy galleries, [Online]. Silver Spring, MD: The American Ivy Society (Producer). Available: http://www.ivy.org/index.html [2010, May 28]. [80144]

166. The Ardens of Delaware. 2010. Why we are removing ivy, [Online]. In: Weed-in-walk tasks--ivy. In: Weed-n-walk in the Ardens. TheArdens.com (Producer). Available: http://www.theardens.com/weedEnglishIvy.htm [2010, June 25]. [80145]

167. The Nature Conservancy. 1998. Vegetation classification of Rock Creek Park. NBS/NPS Vegetation Mapping Program. Arlington, VA: The Nature Conservancy. 50 p. Available online: http://biology.usgs.gov/npsveg/rocr/rocrrpt.pdf [2010, January 25]. [78028]

168. Thimonier, A.; Dupouey, J. L.; Timbal, J. 1992. Floristic changes in the herb-layer vegetation of a deciduous forest in the Lorraine Plain under the influence of atomospheric deposition. Forest Ecology and Management. 55: 149-167. [20845]

169. Thomas, L. K., Jr. 1998. Topographic alterations, forest structure, and invasion by English ivy (Hedera helix L.) in the Rock Creek floodplain, Washington, D.C. Natural Areas Journal. 18(2): 164-168. [78765]

170. Thomas, Lindsey Kay, Jr. 1980. The impact of three exotic plant species on a Potomac island. National Park Service Scientific Monograph Series No. 13. Washington, DC: U.S. Department of the Interior, National Park Service. 179 p. [41748]

171. Thompson, K. 1978. The occurrence of buried viable seeds in relation to environmental gradients. Journal of Biogeography. 5: 425-430. [19769]

172. Tinner, Willy; Hubschmid, Priska; Wehrli, Michael; Ammann, Brigitta; Conedera, Marco. 1999. Long-term forest fire ecology and dynamics in southern Switzerland. Journal of Ecology. 87: 273-289. [30005]

173. Tobe, John D.; Fairey, John E., III; Gaddy, L. L. 1992. Flora of the Chauga River gorge, Oconee County, South Carolina. Castanea. 57(2): 77-109. [72019]

174. Tyler, Marnie W.; Peterson, David L. 2006. Vascular plant species diversity in low elevation coniferous forests of the western Olympic Peninsula: a legacy of land use. Northwest Science. 80(3): 224-238. [65488]

175. Tyser, Robin W.; Worley, Christopher A. 1992. Alien flora in grasslands adjacent to road and trail corridors in Glacier National Park, Montana (U.S.A.). Conservation Biology. 6(2): 253-262. [19435]

176. U.S. Department of Agriculture, Forest Service, Eastern Region. 2004. Eastern Region invasive plants ranked by degree of invasiveness, [Online]. In: Noxious weeds and non-native invasive plants. Section 3: Invasive plants. Milwaukee, WI: Eastern Region (Producer). Available: https://www.fs.usda.gov /r9/wildlife/range/weed/Sec3B.htm [2004, February 16]. [46748]

177. U.S. Department of Agriculture, Forest Service, Southern Region. 2001. Regional invasive exotic plant species list, [Online]. In: Regional Forester's list and ranking structure: invasive exotic plant species of management concern. In: Invasive plants of southern states list. Southeast Exotic Pest Plant Council (Producer). Available: http://www.se-eppc.org/fslist.cfm [2003, August 25]. [44944]

178. U.S. Department of Agriculture, Forest Service. 2001. Guide to noxious weed prevention practices. Washington, DC: U.S. Department of Agriculture, Forest Service. 25 p. Available online: https://www.fs.usda.gov /invasivespecies/documents/FS_WeedBMP_2001.pdf [2009, November 19]. [37889]

179. U.S. Department of Agriculture, Natural Resources Conservation Service. 2010. PLANTS Database, [Online]. Available: https://plants.usda.gov /. [34262]

180. van Ruremonde, R. H. A. C.; Kalkhoven, J. T. R. 1991. Effects of woodlot isolation on the dispersion of plants with fleshy fruits. Journal of Vegetation Science. 2(3): 377-384. [18112]

181. Verdu, M.; Pausas, J. G. 2007. Fire drives phylogenetic clustering in Mediterranean basin woody plant communities. Journal of Ecology. 95(6): 1316-1323. [78828]

182. Vezza, Maurizio; Nepi, Massimo; Guarnieri, Massimo; Artese, Daniele; Rascio, Nicoletta; Pacini, Ettore. 2006. Ivy (Hedera helix L.) flower nectar and nectary ecophysiology. International Journal of Plant Sciences. 167(3): 519-527. [78756]

183. Vidra, Rebecca L.; Shear, Theodore H.; Wentworth, Thomas R. 2006. Testing the paradigms of exotic species invasion in urban riparian forests. Natural Areas Journal. 26(4): 339-350. [65080]

184. Vines, Robert A. 1960. Trees, shrubs, and woody vines of the Southwest. Austin, TX: University of Texas Press. 1104 p. [7707]

185. Waggy, Melissa. 2010. [Personal observation]. Regarding English ivy distribution in Portland, OR area. Missoula, MT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, FEIS. On file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT; FEIS files. [80207]

186. Wagner, Warren L.; Herbst, Derral R.; Sohmer, S. H., eds. 1999 [Revised edition]. Manual of the flowering plants of Hawai'i. Volume 1. Bishop Museum Special Publication 97. Honolulu, HI: University of Hawai'i Press; Bishop Museum Press. 988 p. [70167]

187. Walters, M. Alice; Teskey, Robert O.; Hinckley, Thomas M. 1980. Impact of water level changes on woody riparian and wetland communities. Volume 7: Mediterranean region, western arid and semi-arid region. FWS/OBS-78/93. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service, Biological Services Program. 84 p. [52899]

188. Watt, A. S. 1924. The scrub associes. In: On the ecology of British beechwoods with special reference to their regeneration. Part II. The development and structure of beech communities on the Sussex Downs. The Journal of Ecology. 12(2): 154-160. [72535]

189. Watt, A. S. 1934. The vegetation of the Chiltern Hills, with special reference to the beechwoods and their seral relationships. Journal of Ecology. 22(2): 445-507. [79209]

190. Weber, Ewald. 2003. Invasive plant species of the world: a reference guide to environmental weeds. Cambridge, MA: CABI Publishing. 548 p. [71904]

191. Wells, Elizabeth Fortson; Brown, Rebecca Louise. 2000. An annotated checklist of the vascular plants in the forest at historic Mount Vernon, Virginia: a legacy from the past. Castanea. 65(4): 242-257. [47363]

192. Welsh, Stanley L.; Atwood, N. Duane; Goodrich, Sherel; Higgins, Larry C., eds. 1987. A Utah flora. The Great Basin Naturalist Memoir No. 9. Provo, UT: Brigham Young University. 894 p. [2944]

193. White, David J.; Haber, Erich; Keddy, Cathy. 1993. Invasive plants of natural habitats in Canada: An integrated review of wetland and upland species and legislation governing their control. Ottawa, ON: Canadian Wildlife Service. 121 p. [71462]

194. White, Rickie D., Jr.; Pyne, Milo. 2003. Vascular plant inventory and plant community classification for Guilford Courthouse National Military Park. NatureServe Technical Report: Cooperative Agreement H 5028 01 0435. Durham, NC: NatureServe. 121 p. [79630]

195. Wofford, B. Eugene. 1989. Guide to the vascular plants of the Blue Ridge. Athens, GA: The University of Georgia Press. 384 p. [12908]

196. Wunderlin, Richard P.; Hansen, Bruce F. 2003. Guide to the vascular plants of Florida. 2nd edition. Gainesville, FL: The University of Florida Press. 787 p. [69433]

197. Yost, Susan E.; Antenen, Susan; Harvigsen, Gregg. 1991. The vegetation of the Wave Hill Natural Area, Bronx, New York. Torreya. 118(3): 312-325. [16546]

198. Zomlefer, Wendy B.; Giannasi, David E.; Bettinger, Kelly A.; Echols, S. Lee; Kruse, Lisa M. 2008. Vascular plant survey of Cumberland Island National Seashore, Camden County, Georgia. Castanea. 73(4): 251-282. [75096]