Mountain woodfern is found on sites in the southern Appalachians ranging from wet to dry-mesic [101,104,142]. In red spruce and red spruce-Fraser fir subalpine forests on Mount Rogers, Virginia, relative importance of mountain woodfern is greatest on mesic sites [133].

Most evidence suggests that spinulose woodfern also has a strong affinity for moist habitats. It is found in seasonally flooded habitats where soils are perpetually moist [39,66,90]. Two studies in the northern Great Lakes region indicated that spinulose woodfern abundance was strongly associated with moisture [88,89]. In flood-prone habitats spinulose woodfern grows mainly on hummocks rather than in hollows where there is standing water [31,70]. Although Mohlenbrock [96] indicates that it is rarely found in dry habitats in Illinois, Peet [122] indicated that spinulose woodfern was "primarily confined to drier microsites" in an eastern white pine-dominated forest in Itasca State Park, Minnesota.

Spreading woodfern is also strongly associated with moist habitats. It is an indicator of moist sites in the western hemlock zone of the Gifford Pinchot National Forest, Washington [162]. It is found on moist, floodplain soils in south-central Alaska subject to periodic flooding [48] and on mesic to subhygric sites in coastal British Columbia western redcedar-Douglas-fir-western hemlock forests [110]. Spreading woodfern is a common understory component in wetter areas of old-growth Douglas-fir-western hemlock forests northwestern Oregon [147]. Lackschewitz [78] stated that spreading woodfern "requires more moisture than most other ferns" of western Montana. A study of environmental gradients in the California Coastal Redwood Region showed spreading woodfern distribution is associated with very moist sites (average minimum available moisture=74.5%) [170]. Spreading woodfern is found on fresh to very moist (groundwater table between 1-2 feet (30-60 cm)) soils in coastal British Columbia [73].

Intermediate woodfern may be less strongly associated with moist sites than other woodferns. It is found on mesic sites in northern lower Michigan northern hardwood forests [136]. It is a characteristic herb of mesic to submesic sites in central Appalachian northern hardwood forests [103] and a dominant herb on mesic to dry-mesic sites in eastern hemlock-northern hardwoods forests of the northern and central Appalachians [111]. Oosting [118] suggested that intermediate woodfern requires shade and moisture in North Carolina Piedmont habitats.

Elevation: The following table lists elevational ranges where woodferns occur in western North America. These examples are not necessarily elevational limits to woodfern distribution.

Spreading woodfern is found from coastal to subalpine elevations in the Pacific Northwest [126] and even into the alpine zone in Alaska [137]. In the central and northern Appalachians, mountain woodfern [24] and intermediate woodfern [152] may both be found within a wide range of elevations. In the southern Appalachians, mountain woodfern occurrence is limited to high elevations [24]. Where they cooccur in the northern and central Appalachians, intermediate woodfern tends to be more abundant at low elevations, while mountain woodfern is comparatively more abundant in the high spruce-fir zone ([85] and references therein).

Climate: Woodferns are generally restricted to the cool, moist forests of temperate and boreal North America. Although mountain woodfern is found in high-elevation habitats where the climate is cool and wet in the Appalachians [46,101,104,142], its fronds are considered frost sensitive [76,152]. A review of site conditions in Canada indicates that spinulose woodfern occurs under boreal, cool-temperate, and cool-mesothermal climatic regimes, and its frequency increases with precipitation [134]. Spreading woodfern is found within boreal, cool-temperate, and cool-mesothermal climates in coastal British Columbia [73], and in floodplain forests in south-central Alaska, where snow cover usually remains until late May [48]. Intermediate woodfern is found in Appalachian Mountain habitats where high rainfall and fog deposition [142] and severe winter temperatures, wind, and ice are common [103].

Shade tolerance: Woodferns are generally shade tolerant. Intermediate woodfern ([20] and references therein) and spinulose woodfern [148] are characterized as shade tolerant based on physiological parameters. Spreading woodfern is also characterized as shade tolerant (e.g., [73]). Alaback [4] indicates that spreading woodfern is among the most shade-tolerant understory plants in southeastern Alaska forests. A study of environmental gradients in the California coastal redwood region showed spreading woodfern distribution was associated with shaded habitats where average light intensity was 4.7% of full sunlight [170]. As of this writing (2007), there was no published information discussing the shade tolerance of mountain woodfern. However, since mountain woodfern is found in habitats similar to those of other woodferns, it is reasonable to assume that mountain woodfern is also similarly tolerant of shade.

Succession following stand replacement: Oliver's [116] 4-stage stand development model provides a useful framework for examining how woodferns are likely to respond following stand replacement.

The first years following stand replacement (stand initiation stage) may be the least predictable in terms of woodfern response. Woodfern abundance during this period may be influenced by a number of factors including predisturbance abundance, the nature and severity of the disturbance, and the responses of associated vegetation. Most studies of forest succession following stand-replacing disturbance strongly suggest that woodfern abundance is diminished as resource competition heightens (stem exclusion stage) and then increases once more with understory replacement (understory reinitiation stage). Evidence comparing woodfern abundance in late-seral or old-growth stages with earlier stages of succession is sparse. It seems likely that woodferns persist, if not flourish, in old or late-successional forests that harbored them in previous successional stages.

Alaback [3,4] described secondary succession in western hemlock-Sitka spruce forests in southeastern Alaska, illustrating woodfern response during stand development from stand initiation to old growth. Fern populations in these forests, including spreading woodfern, generally increase in abundance directly following disturbance such as logging or large-scale windthrow, especially where tree and shrub regeneration is initially sparse [3,4]. Ferns tend to decline about 20 to 25 years after disturbance, when shrubs and tree saplings form a dense canopy. At about 50 to 60 years ferns begin to dominate the understory. During the final stages of succession, at around 250 years, understory species diversity increases, with forbs, shrubs, and tree seedlings becoming more common and ferns decreasing in importance [3].

Similar to Alaback's [3,4] characterization, a study of the effect of overstory removal on shrub and herb dynamics in a north-central New Hampshire northern hardwood forest found spinulose woodfern abundance increased slightly following disturbance. Spinulose woodfern occurred in 18.8% of sampling quadrats prior to overstory removal compared with 18.6%, 20.7%, and 23.4% during the first 3 postdisturbance years. Vegetative reproduction of existing ramets, rather than establishment of new genets, accounted for nearly all the postdisturbance spinulose woodferns sampled [69].

Other sources indicate that woodfern populations diminish in the early stages of stand development following stand-replacing disturbance. Siccama and others [144] suggested that woodferns are not a major component of early or midseral succession in the White Mountains, New Hampshire. A study at the Hubbard Brook Experimental Forest, New Hampshire, indicated that spinulose woodfern was suppressed during the first 20 years of succession in a mixed northern hardwoods-red spruce-balsam fir forest [131].

Rapidly diminished woodfern abundance following disturbance may be due, in part, to interference from other plant species. In a southern Appalachian oak-hickory forest, intermediate woodfern was sparse but present (4% average frequency; 0.12% average cover) in undisturbed forest, but was not present in plots sampled 4 years after severe blowdown and 3 years after salvage logging. Average percent cover of groundlayer vegetation was nearly 100% in the disturbed forest compared with just over 20% in a similar nearby undisturbed forest, indicating that interference among groundlayer plants may have been much greater in the recently disturbed forest [41].

A study of changes in forest understory vegetation following stand-level windthrow in east-central Minnesota demonstrates how differences in forest type or the nature of the disturbance may result in strikingly different woodfern successional responses. In eastern white pine-dominated forest, spinulose woodfern frequency increased from little initial occurrence to 12.5 % in postdisturbance years 1 and 2, and to 34.2% by year 14. In an adjacent northern pin oak-dominated forest, very little change in spinulose woodfern frequency occurred over the 14-year study. It was speculated that the difference in spinulose woodfern postdisturbance response between forest types may have been due to differences in effects of the disturbance on overstory trees. Trees in the oak forest tended to snap off at the bole while the pines tended to uproot, creating more bare mineral soil that enhanced spinulose woodfern establishment [119].

Disturbance that kills overstory trees but leaves large numbers of intact snags and an undisturbed understory might also result in unique successional responses. Intermediate woodfern and common woodsorrel (Oxalis montana) comprised most of the initial increase in understory cover following girdling of overstory eastern hemlock trees in southeastern New York [176].

Regardless of how rapidly succession proceeds from stand initiation to stem exclusion, woodferns may be reduced or even eliminated once the ground layer is overtopped by dense regeneration of woody species. A chronosequence study in black spruce-dominated stands in western Labrador indicated that suppression of woodfern populations may last for many years. Average spinulose woodfern cover was 1.09% in 2-year-old stands, then 0% for stand ages 18, 40, 80, and 140 years. Other herbaceous species showed a similar response. Forty- and 80-year-old stands were generally shrub-dominated, while 80- and 140-year-old stands were transitioning to dominance by tree species, mainly black spruce. It was not clear if individual spinulose woodferns in the 2-year-old stands predated the stand-initiating disturbance or if these were recently established, short-lived populations. Overall herbaceous cover remained quite low even in the 140-year-old stands, suggesting that understory reinitiation had not yet begun [145].

The time elapsed between stem exclusion and understory reinitiation may be highly variable. A long-term study of vegetation dynamics in a western Massachusetts mixed conifer-hardwood forest examined the effects of a 1938 hurricane and a subsequent salvage operation. Initial surveys indicated that the predisturbance spinulose woodfern population was greatly diminished in the first decade following the hurricane. Remeasurement of the original plots more than 50 years after the hurricane revealed that spinulose woodfern had reestablished, and understory species composition had become generally similar to prehurricane species composition [84].

In a study of old-growth characteristics in balsam fir forests on the Gaspé Peninsula, eastern Quebec, spinulose woodfern percent frequency was directly related to stand age. Spinulose woodfern frequency in 50-year-old, second-growth stands (characterized by uniform tree cover, predominance of stems <8 inches (20 cm) DBH, high-density, and even-age structure) was 1%, compared with 8% in pristine senescent stands (characterized by the predominance of stems >8 inches (20 cm) DBH, an even-aged structure, and single or collective blowdowns in the last decade) and 21% in old-growth stands (characterized by irregular structure, an uneven-aged mosaic, and trees >90 years old) [33]. In a hybrid spruce (Picea glauca × P. engelmannii) forest in central interior British Columbia, spreading woodfern was found exclusively in late-seral stands (>140 years since fire) and not in midseral (50-80 years since fire) or early-seral stands (<14 years since fire) [37].

Research in the northern mixed hardwood region of central New York comparing herb vegetation between postagricultural forest stands (64-94 years old) and adjacent old stands never cleared for agriculture suggests there may be some species-level differences in woodfern response to succession. Average intermediate woodfern frequency was significantly greater in old forests than in postagricultural stands (P<0.05). Spinulose woodfern frequency was not significantly different between the 2 types (P>0.05), and was similar to the low levels of fancy fern in the younger forests [146].

Two studies of gap dynamics indicate that woodferns may respond positively to canopy gap formation. In an east-central New York upland hardwood forest, spinulose woodfern was significantly more abundant in treefall gaps (P<0.05) compared with closed-canopy transects, in at least 50% of the censuses [53]. In mature eastern hemlock and deciduous forests in southeastern Ohio, spinulose woodfern cover was significantly greater (P<0.05) in canopy gaps (x=31.85%) compared with closed deciduous canopy (x=7.71%) and closed eastern hemlock canopy (x=2.98%) [128].

However, intermediate woodfern had significantly (P<0.05) higher importance values (a function of relative cover and relative frequency) under closed canopy compared with canopy gaps of 60 to 85 m² and 120 to 190 m² in a mixed-conifer swamp forest in central New York [6].

Canopy gap closure rate limits the available time for plant response [27]. A chronosequence of canopy gaps in a southeastern Ohio eastern hemlock forest showed that spinulose woodfern cover peaked 3 years after gap formation [128].

Soil disturbance microsites may also be created when trees are uprooted by windthrow. Over time these small-scale soil disturbances create a mosaic of pits and mounds, enhancing habitat heterogeneity [14]. Studies examining pit/mound topography in old-growth forests suggest a legacy effect that may influence woodfern distribution in these forests, even long after the more ephemeral influence of increased light availability associated with gap formation has waned. In an east-central New York mature sugar maple-American beech forest, spinulose woodfern seedling emergence was significantly greater in soil sampled from treefall pits compared with treefall mounds (P<0.05) [13]. On a pair of sites in a southeastern Alaska old-growth western hemlock-Sitka spruce forest, spreading woodfern importance was related to age since disturbance. On one site, undisturbed forest floor plots and old mounds (>200 years) had significantly higher spreading woodfern importance (P<0.01) than plots with young and intermediate mounds (50 and 150 years). At another site, spreading woodfern importance was significantly higher on undisturbed forest floor plots compared with windthrow mounds of all ages (age classes include mean ages of approximately 50, 150, and >200 years; P<0.01) [32]. A study in old-growth eastern hemlock-American beech forest found that intermediate woodfern percent cover was significantly greater in old treefall pits compared with old treefall mounds and adjacent undisturbed soil (P<0.05). The treefall pits and mounds were assumed to be relatively old, since transect locations were chosen based on showing no sign of the trees that had formed the pits, and mounds and were not located beneath canopy gaps [124].

Intermediate woodfern is evergreen [52,76,127,144,152] or wintergreen [21,24], and the significance of its leaf phenology has been well studied. In the fall intermediate woodfern leaves change from an upright to a prostrate position. This occurs due to a softening of the tissue in a 0.4- to 0.8-inch (1-2 cm) zone of the lower stipe, such that the stipe no longer supports the weight of the frond. Despite bending, the vascular tissue of the stipe remains functional and the leaves remain photosynthetically active throughout winter as long as they remain uncovered. Leaf chlorophyll levels remain high into spring. This mechanical adaptation of intermediate woodfern leaves is thought to minimize water loss during winter [115].

Wintergreen fronds of intermediate woodfern are capable of positive net photosynthesis throughout spring. The highest rates are achieved in early spring just after snowmelt, but positive net photosynthesis occurs even late into frond senescence [158], which occurs in early summer [85]. Tessier [158] articulated that spring carbon gain in wintergreen species such as intermediate woodfern probably represents an important fraction of net annual energy capture. The comparatively high light environment prior to canopy leaf-out provides opportunity for carbon assimilation that is diminished in the shady summer understory. In addition to enhanced carbon capture, early spring nutrient uptake also occurs, coinciding with the highest rates of vernal photosynthesis in these wintergreen fronds [160].

Van Buskirk and Edwards [166] demonstrated the contribution of wintergreen leaves to early spring growth of intermediate woodfern. They paired similarly-sized, proximately-located plants, and excised wintergreen leaves from one plant of each pair prior to commencement of new spring growth. Average growth rate of nonexcised plants was significantly greater than that of plants with wintergreen leaves removed (P<0.005). Within about 2 months frond biomass of intact plants was nearly twice that of excised plants [166]. Tessier and Bornn [159] used labeled ¹³C to demonstrate that vernally fixed carbon from old fronds is translocated to new fronds.

FIRE ECOLOGY

• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

Although woodferns can produce many thousands of spores/plant (see Spore production), spores are thought to be widely dispersed by wind (see Spore dispersal), and propagule banking has been demonstrated, there were no published reports as of 2007 documenting postfire establishment of new woodfern gametophytes. Woodferns may colonize postfire habitats, both from on-site and off-site spores, although this is speculative.

Fire regimes: As of this writing (2007), there were no published studies specifically examining relationships between woodferns and fire regimes. Given wood ferns' affinity for cool, moist sites (see Site Characteristics), it is unlikely that they will be common on sites with frequently recurring fire, although this is speculative. With a few exceptions, the plant communities and ecosystems listed in the table below include fire return intervals that may be hundreds of years.

The following table provides fire return intervals for plant communities and ecosystems where woodferns may occur. Find further fire regime information for the plant communities in which these species may occur by entering the species' names in the FEIS home page under "Find Fire Regimes".

FIRE EFFECTS

• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

Hamilton and Peterson [59] studied vegetation response to clearcutting followed by slash burning of an Engelmann spruce-subalpine fir forest in south-central British Columbia. Cutting occurred over winter in 1988 and 1989, after which the site was divided into 3 treatment areas: a spring burn (7 June), a fall burn (12 September), and an unburned control. Although both burns were considered low severity, the spring burn consumed more of the forest floor (24.9%) than the fall burn (10.4 %). In the fall burn, 47.6% of the depth-of-burn pins showed no measurable duff reduction, compared with 14% of the spring burn pins. Duff moisture code was 28 for the spring burn and 8 for the fall burn, indicating much drier duff in the spring burn. Detailed burn characteristics are available in Hamilton and Peterson [59]. Spreading woodfern frequency was 36% in the unburned plots, 15% in the spring-burned plots, and 33% in the fall-burned plots prior to logging. Spreading woodfern persisted after logging in 3 unburned plots and was observed intermittently on another 3 unburned plots. The more severe spring burn eliminated spreading woodfern from all the plots in which it had occurred prior to burning. Spreading woodfern sprouted in all fall burn plots where it occurred prior to burning. In postfire year 1, spreading woodfern cover was significantly lower in burned plots (P=0.007) compared to unburned plots (P=0.007). Spreading woodfern cover was also significantly lower in spring vs. fall burn plots in postfire year 1 (P=0.05). It was concluded that spreading woodfern "is fairly sensitive to burn severity and could be eliminated by burning" [59].

Long-term effects of fire on woodfern populations may be similar to the effects of other types of disturbance, such as blowndown or logging (see Successional Status). Within woodfern forest habitats, fire and other types of disturbance may similarly affect stand structure.

Chapman and Crow [22] examined the effects of prescribed fire on groundlayer vegetation in an eastern white pine stand in southeastern New Hampshire. Relatively cool, surface-running head fires were conducted in mid-October 1976 and mid-April 1977. Spinulose woodfern was present (no quantitative measure was reported) in both prefire and postfire measurement plots, although it was absent from adjacent unburned control plots. Spinulose woodfern regenerated vegetatively, sprouting rapidly following burning [22].

Multiple, biennial prescribed burns, as well as single burns, conducted in a red pine and eastern white pine plantation in southwestern lower Michigan, yielded no discernible impact on spinulose woodfern presence compared with unburned controls. Fires were low-severity understory burns (<3.3 feet (1 m) flame lengths) in which duff consumption was generally <0.59 inch (1.5 cm) and woody fuels >0.98 inch (2.5 cm) in diameter were unconsumed, although understory vegetation was nearly all top-killed. Treatments consisted of either a) 3 biennial May burns, beginning in 1991, b) a single May, 1991 burn, or c) an unburned control. Mean percentage cover and relative frequency for spinulose woodfern were compiled from sampling conducted every 4 weeks from May to September. Although treatment differences were not statistically tested at the species level, the data suggest that burn treatments had little short-term effect on spinulose woodfern cover or frequency [114]. For a detailed discussion, see the Research Project Summary of this study.

Hamilton and Peterson's [59] study of vegetation response to clearcutting followed by slash burning in a hybrid spruce (Picea glauca × P. engelmannii) forest in interior central British Columbia suggests that spreading woodfern was initially reduced but not eliminated by fire, with spreading woodfern quickly recovering to near pretreatment levels. Cutting occurred over winter in 1987 and 1988, the site was burned in early September 1988, and vegetation data were collected in summer. The fire was considered "low- to moderate-severity" [59]. A more detailed discussion of this study is available in the Research Project Summary of this study.

Hamilton's Research Papers (Hamilton 2006a, Hamilton 2006b) provide further information on prescribed fire and postfire response of plant community species including spreading woodfern.

Regardless of how woodfern abundance is affected in the first few years following fire, short of its elimination, it is likely to decline within a decade or so following stand-replacing fire. In the above study, despite postfire recovery to near-prefire levels by year 3, spreading woodfern abundance showed a subsequent decline in postfire years 5 and 10. Although not part of the study's objectives, comparison of spreading woodfern abundance with total tree species cover data indicates that the decline in spreading woodfern abundance may have been due to interference from tree regeneration [58]. This response is generally predicted by Oliver's [116] 4-stage forest stand development model, in which all the growing space freed by a stand-replacing disturbance becomes occupied by the initial cohort of regenerating plants (stand initiation stage), followed by a stem exclusion stage during which growing space is limited and height stratification excludes many low-growing individuals.

Another study of vegetation response to clearcutting followed by slash burning in an Engelmann spruce-subalpine fir forest in south-central British Columbia [58] yielded results similar to Hamilton and Peterson's [59] (see Discussion and Qualification of Fire Effect for their treatments and results). Vegetation was sampled the summer before cutting, and 1, 2, 3, 5, and 11 years after burning [58].

Differences in cover between burned and unburned treatments were not statistically significant after year 1 (P>0.06), and comparison of cover data between the unburned and fall burned treatments suggests that the spreading woodfern population was unaffected by fall burning, separate from the influence of clearcutting [58]. As in Hamilton and Peterson's [59] study, a decade following clearcutting and slash burning, spreading woodfern abundance was on a downward trajectory [58]. Stand-replacing fire might similarly change the structure of the forest and, assuming spreading woodfern survived the initial disturbance, act similarly on spreading woodfern populations over 10 or so years.

Other studies also suggest that woodferns are not abundant on previously-burned sites, at least during the first few postfire decades. Spreading woodfern cover 15 to 20 years after prescribed burning in Lutz spruce forests of the Kenai Peninsula, south-central Alaska, ranged from 0% to 4%. On prefire and unburned plots, spreading woodfern cover ranged from 1% to 35%. Neither detailed information on immediate fire effects nor fire behavior parameters were provided [19].

In a 25-year-old burn in a mature, southern Appalachian red spruce-Fraser fir forest, mountain woodfern was not present in postfire plots. Although no prefire or unburned vegetation data were provided, it was noted as an important herb-layer species in both mature and second-growth logged red spruce-Fraser fir forests in the surrounding area. Tree-layer data suggest that the fire was mainly stand replacing [140,141].

Long-term studies, while sparse, indicate that response of woodfern populations to fire may be difficult to predict during late-successional stages. Simon and Schwab [145] examined vegetation across a chronosequence of black spruce-dominated stands in western Labrador. Fire-disturbed stands of ages 2, 18, and 40 years, as well as 80- and 140-year-old forest stands of unknown disturbance origin were sampled. Although the stand-originating disturbance was unknown for the older stands, it was noted that stand-replacing fire has been the dominant natural disturbance in the region. Average spinulose woodfern cover was 1.09% in the 2-year-old stands, and 0% for the remaining stands. In a hybrid spruce (Picea glauca × P. engelmannii) forest in central interior British Columbia, spreading woodfern was found exclusively in late-seral stands (>140 years since fire) and not in midseral (50-80 years since fire) or early-seral stands (<14 years since fire) [37].

De Grandpre and others [30] sampled vegetation at 8 southwestern Quebec boreal forest sites. Each site represented a discrete postfire age, ranging from 26 years to 174 years since the last fire. These data suggest that spinulose woodfern presence is probably greatest in early postfire succession in these boreal forests, but that it may persist at lower levels for a substantial time without fire recurrence [30].

This fire study also provides information on postfire responses of plant species in communities that include woods strawberry:

• Research Project Summary: Vegetation recovery following a mixed-severity fire in quaking aspen groves of western Wyoming

MANAGEMENT CONSIDERATIONS

• IMPORTANCE TO LIVESTOCK AND WILDLIFE
• VALUE FOR REHABILITATION OF DISTURBED SITES
• OTHER USES
• OTHER MANAGEMENT CONSIDERATIONS

Palatability/nutritional value: In-vitro simulation suggests that spinulose woodfern is among the most highly digestible moose forage species on Isle Royale, northern Michigan [16].

Cover value: No information is available on this topic.

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