Polystichum munitum appears to be most closely related to P . imbricans based on morphologic (D. H. Wagner 1979) and electrophoretic (P. S. Soltis et al. 1990) analyses. The chloroplast DNA of P . imbricans , however, is divergent (G. Yatskievych et al. 1988), suggesting a chloroplast origin independent of the nuclear genome. That Polystichum munitum is related to P . acrostichoides is supported by data from chloroplast DNA analysis (G. Yatskievych et al. 1988) but contradicted by data from electrophoretic studies (P. S. Soltis et al. 1990).
Polystichum munitum can be distinguished from P . imbricans by its persistent, wide (the largest wider than 1 mm) distal petiolar scales; such scales of P . imbricans are less than 1 mm wide and fall off early.
From an evolutionary standpoint, Polystichum munitum is a diploid progenitor of P . andersonii , P . californicum , P . setigerum , and, perhaps, P . scopulinum . Hybrids with all except P . setigerum have been reported, all triploid, attesting to its parental role in the tetraploids (see discussion under each). Hybrids with P . braunii (A. Sleep and T. Reichstein 1967), P . kruckebergii (P. S. Soltis et al. 1987), P . dudleyi (W. H. Wagner Jr. 1973), and P . lemmonii (P. S. Soltis et al. 1989) also have been reported.
The population on Guadalupe Island has been called Polystichum solitarium Maxon.
Botanical description: This description covers characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [10,58,98,100,106,126,130,170,183]). Morphological similarity among Polystichum species may make identification difficult [58].
Western swordfern populations consist mostly of sporophytes; gametophytes are extremely rare [189], and no description of western swordfern gametophytes was found in the literature. The following description applies to sporophytes.
Western swordfern is a medium-sized, perennial, long-lived, evergreen fern [170,189] with many leaves (fronds), sometimes 75 to 100 [155], clustered on a short, vertical rhizome [126]. Stems are erect or ascending and fronds arch outward [58,126], forming a crown [36,155,170,175]. Fronds are leathery and stay evergreen for several years; withered fronds remain attached to the rhizome [131]. Frond size varies depending on location and site conditions and may range from about 8 to 98 inches (20-250 cm) long [36,58,74]. Fronds are usually at the smaller end of this range in northern [7,106,170] and inland [126] parts of western swordfern's distribution, and in sunny places [106]. Plants with fronds >3 feet (1 m) long typify western swordfern where it is an understory dominant [100,170,216]. Petioles are one-eighth to one-fourth the length of the frond, densely scaly, and gradually diminishing in size distally. Leaflets are 0.4 to 6 inches (1-15 cm) long. Those of shade-growing plants occur in 1 plane; those of sun-growing plants are twisted or contorted [58]. Sori are large and circular [170] and occur in 1 to several rows [106] on leaflets (Figure 6).
Western swordfern is closely related to narrowleaf swordfern based on morphologic [216] and electrophoretic analysis [191]; it is possible that some of the older literature misidentified these species. When western swordfern plants are subjected to increased insolation (e.g., after canopy removal, in rocky outcrops, or at high elevations), the fronds become dwarfed and more erect, and the leaflets become crisped and more crowded, such that it more closely resembles narrowleaf swordfern [216].
Western swordfern rhizomes are stout, woody, and scaly [36,170], often covered with old stipe bases and ending in a crown of new fronds [106]. Rhizomes are short [100], and plants grow in separate, individual clumps [213] but often form extensive populations [175]. Populations can cover very large areas and consist of thousands of individuals. Disjunct populations east of the Cascade Range are typically smaller, consisting of a few hundred individuals [189].
Characteristics of western sword plants (clonal fragments) were described on 3 sites on the Olympic Peninsula occupied by densely stocked, second-growth forests, 40 to 60 years after clearcutting (Table 6). Clonal fragments consisted of all live plant parts (rhizomes, stolons, roots, buried apical buds, and aerial shoots) connected to an initially selected, undamaged aerial shoot. Most western swordfern clonal fragments consisted of a single rhizome segment that thickened with the production of new fronds, although 5% had more than one ramet emerging from a branched rhizome. Perennating buds were shallow, ranging in depth from about 0.2 to 1.8 inches (0.5-4.5 cm). Roots were wiry and densely branched, mostly occurring in the top 8 to 12 inches (20-30 cm) of soil and spreading laterally in the upper organic horizon; maximum root depth was about 28 inches (72 cm). Soils were silt loams and very gravelly sandy loams, and the thickness of the organic horizon ranged from about 0.4 to 2 inches (1-5 cm) [132].
Table 6. Characteristics* of western swordfern rhizomes, roots, and shoots in young coniferous forests on the Olympic Peninsula, Washington (n=20 western swordfern clonal fragments) [132] Rhizome Root Shoot Total length (cm) Max. diam (mm) Lateral spread (cm) Max. length (cm) Max. spread (cm)** No. of ramets Plant height (cm)*** 5.9Western swordfern occurs along the Pacific Coast from southeastern Alaska south to Baja, California [81,100,126,183], with disjunct populations in northeastern Washington, northern Idaho, northwestern Montana, northeastern Oregon [130,189], and the west Kootenays in British Columbia [74]. Western swordfern is most abundant and widespread in coastal areas from central Vancouver Island and the adjacent mainland southward [170], throughout the western Coast and Cascade ranges [81,100], and into northwestern California [98]. Its latitudinal distribution is described as low-subarctic, high-temperate [183].
Western swordfern occurs in the following states and provinces as of 2014:
United States: AK, CA, ID, MT, OR, PA, SD, WA
Canada: BC [214], YT [158]
In Mexico, western swordfern occurs on Guadalupe Island [58,98]. According to NatureServe [158], it occurs in Yukon Territory, is nonnative in Pennsylvania, and may be extirpated in South Dakota. It is naturalized in Europe [58].
Western swordfern is generally resilient to canopy-opening disturbance and fire effects (see Secondary succession and Plant response to fire), and it is present in most stages of succession in the forests where it occurs as an understory dominant. However, it may be reduced or eliminated after severe soil disturbance [16]. Therefore, while it is likely to persist following wild or prescribed fire in most of its main habitats, it may be sensitive to fire suppression activities that disturb the soil. This is especially true at the extremes of its range where it occurs in lower abundance or is more sensitive to environmental extremes and is more likely to be stressed.
Slash burning has variable effects on western swordfern, depending mostly on site conditions, soil disturbance, and fire severity (see Secondary succession). A series of studies on the HJ Andrews Experimental Forest found that recovery of western swordfern declined as disturbance severity increased, whether by burning or mechanical damage, and cover of western swordfern tended to increase gradually with time since disturbance [52,78]. Disturbance severity was evaluated and sites were classified according to degree of soil disturbance: undisturbed; disturbed-unburned (litter removed or mixed with mineral soil, but little or no evidence of fire); lightly burned (surface litter was charred by fire but not completely removed); and heavily burned (surface litter completely consumed) [76]. Immediately after logging and slash burning, western swordfern was most abundant on undisturbed sites and occurred to a limited extent in disturbed areas. Some plants occurred on lightly burned areas, but none on severely burned areas [51,52]. On undisturbed sites, fireweed dominated early succession, followed by dramatic but temporary release of the residual trailing subshrub common whipplea, which was followed by recovery of the initially dominant western swordfern. In contrast, heavily burned sites were dominated initially by annuals such as nonnative woodland ragwort, tall annual willowherb, and Siberian springbeauty; secondarily by biennials and small-statured perennials; and subsequently by tall woody perennials such as snowbrush ceanothus, redstem ceanothus, and thimbleberry. Western swordfern was not abundant on these sites [76]. See the Research Project Summary of these studies for additional details. For detailed planning and operational considerations for slash burning, including determining site and/or community sensitivity and advantages and disadvantages to burning in different seasons, see Hawkes and others [92].
On the Clearwater National Forest, northern Idaho, western swordfern is among several plant species that have been identified as indicators of sites with high risk of mass movement because they are also indicators of high levels of soil moisture. Mass movement is more likely to occur on these sites following canopy-opening disturbances such as fire (review by [187]).
Western swordfern is an important plant in mountain beaver habitat, and postfire changes in plant community composition may have negative impacts on mountain beavers in some areas. In October 1995, a wildland fire burned about 12,400 acres (5,000 ha) on the Point Reyes Peninsula, California. Postfire surveys (2 to 6 months after the fire) in coastal sage scrub indicated that mountain beaver burrow openings were fully exposed, and only 0.4% to 1.7% of mountain beavers within the burned area survived the fire and immediate postfire period. The fire initially reduced vegetation to a few charred skeletons of the larger shrubs and the charred bases of western swordferns, and in some areas vegetation changed from dense western swordfern before the fire to stands of thimbleberry and blackberry. Even where mountain beavers survived the fire, little or no recovery of mountain beaver populations was detected 5 years later [55].Fuels: Fuels tend to be abundant in coastal forests where western swordfern communities commonly occur, but they are usually too moist to burn except under extreme weather conditions [1]. Literature describing fuel characteristics in coastal forests was lacking as of 2015. Agee and Huff [4] describe fuel characteristics and potential fire behavior at each stage of postfire succession in western hemlock-Douglas-fir/western swordfern communities in the Olympic Mountains, where time since fire ranged from 2 to 515 years. Grier and Logan [72] give detailed information on biomass accumulation and distribution, organic matter distribution, and average litterfall for each of 5 understory community types, including a cool, moist, bigleaf maple-western swordfern community, in 450-year-old Douglas-fir forests in western Oregon [72]. A study on Roosevelt elk use of forage in logged areas in southwestern Oregon reported that the effectiveness of slash burning differed among understory communities. In the western swordfern community, where fuel moisture was high, only 10% of the area burned completely, while in the drier Pacific rhododendron and vine maple communities more than 90% of the area burned [87].
FIRE REGIMES: Western swordfern is a common understory dominant in Douglas-fir, western hemlock, and Sitka spruce forests that have FIRE REGIMES characterized by long-interval, stand-replacement and mixed-severity fires. However, it is also a dominant in communities that historically had more frequent surface and mixed-severity fires, such as redwood forests and Oregon white oak woodlands (Appendix B, Appendix C).
Western swordfern is a dominant or indicator species in several associations in coastal forests of the Pacific Northwest. Due to low lightning incidence and high fuel moisture content year-round, conditions favorable for large wildfires develop only briefly every few years during severe drought. Strong, dry, east (foehn) winds occasionally blow in western Washington and Oregon, causing severe fire conditions. Thunderstorms are uncommon but concentrated in some years over mountainous terrain [136]. British Columbia's coastal temperate rainforests have a wet climate and are rarely impacted by stand-replacing fire. This results in a structurally complex, multiage, multicanopy, old-growth forest with large volumes of living and dead wood [141]. Large lightning fires in Olympic National Park are usually associated with low relative humidity, prolonged drought, short-term dry spells before and after ignition, and locally strong winds [105].
A fire history of the Olympic Mountains indicates that lightning fires were responsible for most of the ignitions prior to 1850, and human-caused fires were likely prevalent during the period of European settlement, 1880 to 1910. Forests on the east side of the Olympics are generally younger than those on the west side. Most of the east side was thought to have burned about 300 years ago, while the west side consists of vast expanses of forest greater than 300 years old. The west side is less prone to burning due to its wetter climate [105]. Western swordfern is a common understory dominant in plant communities on the Olympic National Forest (Table 12), and it is usually present in all ages of stands with average cover often exceeding 20%, although it may be inconspicuous or absent in second growth [97].
Table 12. Fire and other disturbances in forested plant associations of the Olympic National Forest where western swordfern is a named understory dominant [97]. Plant association Fire and other disturbance history western hemlock/dwarf Oregon-grape/western swordfern The typical area of this type has burned once or twice in the last 500 years, although most old stands of this type have been logged. Most old growth that remains is either about 280 or 450 years old. western hemlock/Pacific rhododendron/western swordfern The typical area of this type has burned once or twice in the last 300 years. Most areas have been logged or burned, so little old growth remains, and most stands are less than 80 years old. western hemlock/western swordfern-redwood-sorrel Little of this type has burned in the last 500 years, and most stands are very old. Some younger stands have originated from windstorms or small fires. western hemlock/western swordfern-foamflower The typical area of this type has burned once or twice in the last 700 years. Western swordfern is usually present in all ages of stands, although it may be inconspicuous or absent in densely stocked second growth. Pacific silver fir/western swordfern The typical area of this type has burned once or twice in the last 500 years. Pacific silver fir/western swordfern-redwood-sorrel The typical area of this type has burned very seldom in the last 500 years, and most stands are very old. Some younger stands have originated from windstorms or small fires.The following examples of fire regime information from other areas where western swordfern occurs demonstrate the range of fire regime characteristics with which this species may be associated. The western hemlock/western swordfern-redwood-sorrel association was the most extensive successional community on alluvial landforms in the McKenzie River Valley, Oregon. Stands were 200 to 500 years old, and evidence suggested that most areas of this association had been through 1 or more fires. The Douglas-fir/California hazelnut/western swordfern associations occurred on sites that had burned within the last 100 to 200 years [89]. On Yellow Island, San Juan County, Washington, which had not been logged or grazed, western swordfern was a dominant understory species in Douglas-fir forest. The fire rotation for the island was estimated at 83 years; this frequency was probably influenced by humans [3]. Western swordfern is a typical understory dominant in Oregon white oak forests in the Willamette Valley, where wildfires were common prior to European settlement. After European settlement in the mid-1800s, fires became less frequent and Oregon white oak savannas developed into forests [203]. In the Blue Mountains of northeastern Oregon, western swordfern occurs in cool, moist grand fir stands, where long fire-return intervals and moderate-severity fires may be typical. Most of these locations are lower slopes or near riparian areas and may exist as residual stringers that do not burn as often as associated uplands [2].
At the extremes its range, soil and canopy disturbance may make sites uninhabitable for western swordfern, so it is more common in communities with long intervals between disturbances. For example, in western redcedar-western hemlock forests of northern Idaho, western swordfern had low frequency (1%-2%) on plots in seral shrub communities (2 to 60 years old) regardless of disturbance history (logging with and without pile or broadcast burning), but it occurred in only trace amounts on plots burned multiple times [154]. In northern Idaho, western swordfern seems to be most common in communities with long fire-return intervals. It is an "important forb" in warm, dry to moderate interior Douglas-fir, grand fir, and ponderosa pine habitat types with presettlement FIRE REGIMES of frequent, low- or mixed-severity fire and occasional stand-replacing fire. It "occurs widely" in moderate and moist grand fir habitat types with variable presettlement FIRE REGIMES ranging from high-severity fires followed by persistent shrub fields, to areas where evidence of historic fire is difficult to find. It is "common" in mature and late-successional stands in moderate and moist western redcedar and western hemlock habitat types, where stand-replacing fires probably occurred at intervals of 200 to 250 years (review by [187]).
See the Fire Regime Table for additional information on FIRE REGIMES of vegetation communities in which western swordfern 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".
Several mammals eat western swordfern, including elk, black-tailed deer, mountain beavers, American black bears (review by [74]), and mountain goats [103]. Western swordfern communities also provide habitat for several bird species (e.g., [159,180,220], Table 13). Western swordfern was apparently not eaten by domestic sheep in a Douglas-fir plantation in the Oregon Coast Ranges [174]. However, another study in coastal Douglas-fir plantations found that domestic sheep consumed a lot of ferns, although it was unclear how much of their forage consisted of western swordfern [184].
A review suggests that American black bears sometimes forage on western swordfern [74], and a study from Olympic National Park identified western swordfern in mountain goat fecal pellets collected in late winter or spring [103]. However, most information regarding wildlife use of western swordfern concerns elk, black-tailed deer, and mountain beaver.
Western swordfern is an important elk food in Douglas-fir forests [67] and other habitats in Oregon and Washington [87,97,102,109,148]. Jenkins and Starkey [108] provide a summary of Roosevelt elk use of western swordfern throughout the Pacific Northwest. The elk consumed an abundance of ferns, including western swordfern, during winter and spring [108]. On the Olympic Peninsula, western swordfern is seasonally important for elk [97,102]. Western swordfern was one of the 10 most frequently used elk foods in the southern Oregon Coast Ranges, and the western swordfern-redwood-sorrel habitat type provided much of the food for elk in both clearcuts and undisturbed forests [16].
Western swordfern is a moderately important food for black-tailed deer year-round [38,74]. Western swordfern made up 13% of the annual diet of black-tailed deer at one site (review [74]), and was found in 27 of the 178 stomach samples from black-tailed deer in western Washington [27]. Western swordfern was among the most common species browsed by mule deer in the western hemlock/salal/western swordfern and the Pacific silver fir/western swordfern-redwood-sorrel associations on the Olympic National Forest. Deer sign was frequently observed, and recent activity was noted in late summer [97]. Klein [117] observed heavy spring use of western swordfern by mule deer on Coronation Island in southeast Alaska, despite its apparent low palatability.
Western swordfern is an important plant in mountain beaver habitat from British Columbia to California, providing both food and cover [55,74,81,94,137,176]. Mountain beavers as young as 7 weeks old eat western swordfern [137]. Mountain beaver may be abundant in western swordfern sites in western Oregon [81], where western swordfern is an important winter food [74]. Western swordfern is a favorite mountain beaver food on the Siuslaw National Forest, and mountain beaver populations may be especially large in the moist stands of the western hemlock/Pacific rhododendron/western swordfern association [94].
Western swordfern communities provide habitat for several species of birds. In the Sitka spruce and western hemlock zones on the Olympic Peninsula and in the North Cascade Range, western swordfern is an understory dominant in old-growth forests providing northern spotted owl habitat [159]. In western Washington, it is among the dominant understory species in second-growth Douglas-fir forests (after logging and fire) that serve as drumming sites for Pacific ruffed grouse. The 2 dominant species of ground vegetation at drumming sites are western swordfern and salmonberry (the abundance of one correlates with the scarcity of the other). Ruffed grouse select drumming logs that are higher than surrounding growth of western swordfern [180]. A census in coniferous forests of the central Oregon Cascade Range showed that several species of birds used the 3 habitats shown in Table 13, which all contain substantial western swordfern cover.
Table 13. Population density (individuals/km²) of breeding bird species recorded in a June 1972 census in the central Oregon Cascade Range [220] Bird species Plant community (western swordfern cover) Douglas-fir/creambush oceanspray (8%) western hemlock/Pacific rhododendron/dwarf Oregon-grape (3%) western hemlock/vine maple/western swordfern-redwood-sorrel (22%) yellow-bellied sapsucker --- 151 --- hairy woodpecker --- --- 27 Hammond's flycatcher --- 46 --- western flycatcher 212 175 367 Steller's jay 7 7 83 chestnut-backed chickadee 399 170 154 red-breasted nuthatch 356 --- 101 brown creeper --- 125 541 winter wren 135 76 326 American robin 18 46 --- hermit thrush 14 --- --- Swainson's thrush 145 --- 91 golden-crowned kinglet 135 135 539 hermit warbler 75 78 113 western tanager 86 113 50 Oregon junco 196 290 226Palatability and nutritional value: Information on palatability and nutritional value of western swordfern was very limited in the available literature (2015). One source rated western swordfern as moderately palatable to big game [75] and another characterized it as having low palatability to slugs [30].
Klein [117] provides information on nutritional content of western swordfern collected on 2 dates from Coronation Island, Alaska. Western swordfern had the lowest protein content among deer forage species analyzed [117]. In samples collected between 15 January and 15 February in the White River drainage of western Washington, it averaged 29% in vitro dry-matter digestibility and 11% crude protein [109].
Palatability and nutritional value of western swordfern may differ between logged and unlogged forests. On southern Vancouver Island, western swordfern growing in a recently logged area was described as "still struggling for survival in the newly logged and burned area" and was seldom eaten until winter (when preferred browse was less available). Conversely, western swordfern growing on an older burn site was preferentially selected and eaten by black-tailed deer in summer [38]. Happe and others [86] provide information on nutrient content and astringency in current annual growth of western swordfern and other browse species collected in old-growth forest and 5- to 15-year-old clearcuts on the Olympic Peninsula during summer, fall, winter, and spring.
Cover value: Western swordfern habitats may provide cover for large and small animals. Mule deer and elk use of the western hemlock/vine maple/western swordfern association on the Willamette National Forest is moderately high, mostly for thermal cover. The dense shrub layer also provides good hiding cover [95]. In the western hemlock zone of the Gifford Pinchot National Forest, the western hemlock/devil's-club/western swordfern association provides exceptional hiding cover for big game [208]. On one plot in the western hemlock/western swordfern-foamflower association on the Olympic National Forest, a newborn elk was observed, indicating that the site was used as a calving area [97].
Western swordfern was used as bedding material in winter dens by American black bears in coastal British Columbia. One American black bear habitat was dominated by large Douglas-fir and western redcedar with an understory characterized by western swordfern, foamflower, sweet after death, and lady fern [44].
Mountain beaver and vagrant shrews may prefer western swordfern habitats. Western swordfern provides both food and cover for mountain beaver from British Columbia to California (see Importance to Wildlife). The western hemlock/vine maple/western swordfern association on the Siuslaw National Forest is prime mountain beaver habitat. Mountain beaver were present in over 40% of the plots in that type [94]. In 40-year-old western redcedar and western hemlock stands in British Columbia, the vagrant shrew favored mesic habitats under western redcedar, where western swordfern provided understory cover (review by [164]).
Western swordfern is among several forest products in the Pacific Northwest that may require special management considerations to be sustainable. For example, repeated harvesting of western swordfern fronds reduces frond length and plant survival considerably (review, [40]).
The presence of seeps or super-saturated soils typical in western swordfern habitats indicates that these areas are susceptible to soil compaction or erosion [208].
Because western swordfern may interfere with post-logging regeneration, it has been the object of herbicide applications. Information on studies pertaining to that topic can be found in these references: [35,74,149,195].
Climate change: Fog frequency has declined over the past 50+ years along the Pacific Coast of the western United States (Johnstone 2008, as cited by [134]), which has reduced the frequency of summertime leaf-wetting events. Considering the demonstrated importance of fog water for redwood forest plants, including western swordfern (see Climate in the Site Characteristics section), it seems likely that levels of plant water stress will increase in coastal communities as this important water subsidy is lost [134].
Commercial harvesting of floral greens, including western swordfern [5], began in 1915 and remains one of the most enduring and stable year-round nontimber forest products industries in the Pacific Northwest [54,211]. Enormous quantities of western swordfern leaves are gathered for backgrounds in floral displays; the evergreen leaves keep well in cold storage and are even exported to Europe [58]. Western swordfern requires partial shade to grow in forms acceptable for commercial harvest (with deep green, broad, spreading leaves). See Table 5 for information on which forest zones have the greatest potential for western swordfern production [181].
Western swordfern is used extensively for landscaping [58].
American Indians used western swordfern for a variety of purposes, including household tasks and applications, food, and medicine. Northwest coastal peoples used western swordfern leaves to line pits for cooking [54,81,170,210], to layer between food in baskets, drying racks, and storage boxes [170,210,221], and to cover floors and beds [81,170,210]. Western swordfern leaves were used in a traditional game known as pala-pala [170]. The species also played a part in Kwakiut'l mythology and so was used in rituals [210]. The large, basal clump of leaves and the rhizomes of western swordfern were used as food by several tribes. They were roasted or steamed, peeled, and eaten [81,170,210,221]
Traditional medicinal uses of western swordfern include rhizomes eaten to cure diarrhea [170], young leaves chewed and swallowed for sore throat or tonsillitis, an infusion of boiled rhizome used on sores and to ease pain, and a tea from boiled stems used in labor [81]. Aerial parts of western swordfern are used to stimulate digestion in ruminants [129].
Western swordfern populations consist mostly of mature plants, with small, juvenile plants present in low numbers; gametophytes are extremely rare. Reproduction in western swordfern is mostly by sexual means. High levels of genetic variation in western swordfern suggest that spores disperse away from parent plants (sporophytes) and that gametophytes usually cross with other gametophytes rather than self-fertilize. Vegetative reproduction is limited [189]; it can regenerate from rhizomes after top-kill but does not spread vegetatively [35].
Pollination and breeding system: The mating systems of Polystichum species are outcrossing, and western swordfern is highly outcrossing [189,190]. Rates of intragametophytic selfing in western swordfern range from 0% to 3% [189].
Hybrids are frequent where 2 or more Polystichum species occur. Sterile hybrids are recognized by their misshapen sporangia [58].
Spore production: Most medium-sized forest ferns such as western swordfern begin to produce spores between 1 and 5 years of age, and spore production takes place very regularly from year to year. Most ferns similar in size to western swordfern produce tens of millions of spores on each frond [74].
Spore dispersal: Western swordfern spores are primarily wind-dispersed [189] but are also dispersed by other means [35,74]. The tiny spores are ejected into the air when mature and are carried away by gravity, wind, water, or animals. Fern spores can travel thousands of miles, but in forests there may be a lack of air current to carry them aloft. Airborne spores are often brought down during rainstorms [74].
Spore banking: No information was available in the literature regarding western swordfern spore persistence under field conditions. Under ideal conditions (e.g., dry storage), fern spores may remain viable for 2 to 4 years, but viability and speed of germination decrease with age. Fern spores in a dry, resting state are resistant to physical extremes. They can withstand intense radiation and very low temperatures but are reportedly very sensitive to temperatures above 131 °F (55 °C) (review by [74]).
Germination: Fern spores usually germinate only after being soaked in water. Spores of western swordfern germinate best when exposed to light, but some germination occurs in darkness (review by [74]). In the laboratory, western swordfern spore germination rate was >20% in light and 2% to 10% in the dark [218].
Gametophyte establishment and plant growth: Very little information was available regarding western swordfern gametophyte establishment (as of 2015). One source says that gametophytes are extremely rare in western swordfern populations [189]. Another source notes that western swordfern and other ferns establish from spores on fresh alluvium following deep sediment deposition in redwood forests on alluvial terraces; the new alluvium is rich in nutrients and is an excellent seedbed [20].
Vegetative regeneration: Vegetative reproduction in western swordfern is limited [189]; it can regenerate from rhizomes after top-kill but does not spread vegetatively. Fronds have determinant growth and do not grow back. New fronds emerge from rhizomes early each growing season [35] and after top-kill or removal. Heavy cropping of western swordfern does not reduce cover for long; new fronds quickly regain cover after old ones have been removed [199].
Western swordfern rhizomes may become highly branched with age but are not creeping or spreading [74,189]. Most western swordfern plants studied on the Olympic Peninsula consisted of a single rhizome segment supporting a single ramet; 5% of the plants had more than one ramet emerging from a branched rhizome [132] (see Botanical Description). Although the species often occurs in pure, uniform stands, these stands probably represent populations of individual sporophytes rather than colonies [74].
Western swordfern is widespread in the understory of mesic coniferous and moist mixed-evergreen forests at low to middle elevations (sea level to 7,200 feet (0-2,200 m)) along the northern Pacific Coast [36,58,100,121,126,170,189]. It is among the most common herbaceous species and is often dominant on nitrogen-rich or moist sites in forest habitats where western hemlock and/or coast Douglas-fir (hereafter, Douglas-fir) are characteristic species. These forests occur throughout low-elevation western Washington and on the western slopes of the Cascade Range, around the margins of the Willamette Valley, and in the Coast Ranges [31]. Western swordfern sometimes codominates the understory of oak and dry Douglas-fir forests and woodlands west of the Cascade Range in the Puget Lowlands, Willamette Valley, and Klamath Mountains. It is especially common on sites that formerly supported grasslands and savannas in these areas [32]. Western swordfern may dominate the herb layer in lowland riparian areas west of the Cascade Crest from British Columbia south into northwestern California. These habitats are typically comprised of tall (6-30 feet (2-9 m)), deciduous shrublands, woodlands or forests, or some mosaic of these. Red alder is the most widespread tree species [33].
Climate: Western swordfern thrives in humid coastal climates with mild winters. It also occurs in areas of moist, relatively mild continental climate in northern Idaho, northwestern Montana, and adjacent areas of British Columbia, but in these areas it tends to be restricted to shaded, moist, northern aspects [74,154]. Its frequency and abundance decrease with increasing elevation and continentality [41,121,175].
Western swordfern is among the most typical and abundant understory plants in Sitka spruce [88] and redwood [41] forests along the Pacific Coast. Sitka spruce forests are limited to a relatively narrow oceanside strip characterized by mild winters, cool summers, and abundant moisture throughout the growing season [88]. Extremes in moisture and temperature are rare; the climate is uniformly wet and mild. Precipitation averages about 80 to 120 inches (2,000-3,000 mm) [64], but may reach 220 inches (5,600 mm) in some areas of Alaska and British Columbia [165]. Frequent fog and low clouds add moisture during the relatively drier summer months [64]. Climate in the redwood forest zone is similarly characterized as moist and temperate [66], with high rainfall and dense, dripping fog [205]. Annual precipitation averages nearly 60 inches (1,500 mm), of which 10% to 25% falls in the warmest months and 60% to 70% from December to March [66]. Plants in redwood forests depend on fog absorbed through foliar uptake to stay hydrated during the relatively dry summer [133]. The high foliar uptake capacity of western swordfern may allow it to rely completely on fog water during the summer, when fog exposure is frequent ([134], but see Other Management Considerations). Western swordfern's foliar uptake capacity and morphological characteristics vary with latitude in the redwood forest zone (Table 1), with its greatest foliar uptake capacity in the central part of the zone and no foliar uptake capacity at the southern end [133].
Table 1. Mean (SD) size and abundance of western swordfern crown and fronds measured inside plots at each of 7 old-growth redwood forest sites in California where western swordfern was the understory dominant. Sites are listed from northernmost to southernmost [133]. Site Crown countThe climate in the western hemlock forest zone is wet and mild but varies with latitude, elevation, and location in relation to mountain massifs. Moisture and temperature extremes are greater farther inland [64]. Precipitation occurs mainly during the winter, with brief summer droughts [64,173], and averages about 30 to 170 inches (800-4,400 mm) annually. Precipitation falls mostly as rain or cloud drip, with minimal snow accumulations [169,173,181]. While western swordfern's evergreen fronds are presumably somewhat resistant to frost, they may limit its ability to survive in areas with cold winters [74]. It is not common on sites where snow pack is deep [81,131], and western swordfern associations typically occur where little snow falls (e.g., [97]).
Site characteristics: Western swordfern tolerates a range of site characteristics, from the coastal fog belt to montane and subalpine sites [16]. It is an indicator of mesic and moist, nutrient-rich environments in western hemlock and Douglas-fir forests in western Oregon and Washington [4,39,81,94,131], and it is an indicator of moist, nutrient-rich, humus-rich forests and shaded slopes in British Columbia [121,175]. Plant associations where western swordfern is an understory dominant typically occur at low elevations on productive soils, especially those enriched by surface flow of fine organic materials [175]. Soils typically remain saturated throughout the year due to subsurface water from upslope [81,131], flat topography with impeded soil drainage [118,169], near proximity to surface water, high precipitation, high humidity, or frequent fog (see Moisture relationships for more information).
Western swordfern associations often occur on sites with high timber productivity; these sites are frequently logged [64,161]. The western hemlock zone includes some of the most productive forest land in the Pacific Northwest [64,82,208], and communities where western swordfern dominates the understory are some of the most productive among these [64,65,71,95,97,198,208]. Impressive stands of Douglas-fir, western hemlock, and western redcedar are possible [65], with sparse shrub layers and well-developed herb layers that are often described as lush or luxuriant, because of abundant western swordferns [53,62,64]. High moisture availability and nutrient-rich soils contribute to the high productivity of these sites [64,119]. In British Columbia, for example, these sites typically occur on valley bottoms and relatively flat alluvial terraces close to rivers. Soils are from base-rich parent materials and have loamy textures with high soil moisture holding capacity, few coarse fragments, and good drainage [119].
Western swordfern may reach its best growth and greatest abundance in undisturbed, old-growth stands, especially those dominated by western hemlock or Sitka spruce (Table 2); lush growth of western swordfern may indicate late-successional or relatively undisturbed sites. Western swordfern accounted for almost all understory cover in the central, protected valleys of Sucia Island, Washington, where vegetation is undisturbed, wind is minimal, summer temperatures are low, and soil moisture is high. Its fronds had a spread of nearly 7 feet (2 m) [61].
Table 2. Western swordfern cover and site characteristics in remnant old-growth forests in the North Coast Range of Oregon [70]. Plant association Western swordfern cover (%) Elevation (feet) Precipitation (inches) Moisture group* Slope (%) Aspect (degrees) Slope position Sitka spruce/redwood-sorrel 40.0 1,200 110 41 73 slope, upper 3rd Sitka spruce/redwood-sorrel 16.7 1,500 112 30 297 slope, upper 3rd western hemlock/redwood-sorrel 12.3 1,300 137 wet 11 193 bench western hemlock/redwood-sorrel 34.0 1,180 118 wet 59 150 slope, lower 3rd western hemlock/redwood-sorrel 41.3 1,860 145 39 154 bench western hemlock/vine maple/western swordfern 40.0 1,320 110 wet 71 181 slope, lower 3rd western hemlock/vine maple/western swordfern 28.3 1,400 107 mesic 41 200 bench western hemlock/salal 13.7 480 105 mesic 52 215 slope, lower 3rd western hemlock/Pacific rhododendron-salal 1.4 1,300 88 mesic 54 215 slope, middle 3rd western hemlock/dwarf Oregon-grape-salal 6.0 1,570 97 mesic 59 133 slope, middle 3rd western hemlock/vine maple-California hazelnut 4.3 2,030 90 dry 49 154 slope, upper 3rd grand fir/California hazelnut/white insideout flower 18.3 1,100 61 dry 41 329 slope, upper 3rd grand fir/California hazelnut/white insideout flower 3.0 1,200 65 dry 31 29 rounded ridge top *Identified only for Douglas-fir-dominated stands >200 years old.Western swordfern tolerates disturbance and is common in second-growth forests after logging and other disturbances (see Successional Status), and sometimes occurs even in highly disturbed areas. For example, it was common along electrical transmission rights-of-way in western Washington and Oregon, where it ranged in cover from 2% to 55% [185]. It was noted as particularly common along roadside clearings in southern coastal British Columbia [36].
The following discussion describes common site characteristics of western swordfern communities and gives examples showing its range of site tolerances. This information comes almost exclusively from vegetation classifications, although a few studies were available (as of 2015) that examined western swordfern site affinities. For example:
See the following vegetation classifications for details about western swordfern plant communities: [6,53,64,65,94,95,97,208]. See the following vegetation classifications for descriptions of western swordfern communities in specific locations: [16,53,94,95,99,143,208].
Elevation, landform, topography: Western swordfern is most common at low elevations, but it occurs from sea level to about 7,200 feet (0-2,200 m) [58]. It is widespread in the western hemlock zone in the Pacific Northwest, which occurs from about 490 to 1,800 feet (150-550 m) in wet environments, such as the western slopes of the Olympic Mountains [64], and from sea level up to about 4,000 feet (1,200 m) in relatively drier environments [64,97,181]. Western swordfern is most common up to about 2,500 feet (760 m) on the Olympic National Forest [131]. In California, it occurs below 5,200 feet (1,600 m) [98]. It rarely occurs above 3,000 feet (900 m) in southwestern British Columbia, or above 300 feet (100 m) on the northern coast of British Columbia [74]. Plants at high elevations near the coast may be stunted or sparse (e.g., at 6,300 feet (1,920 m) in the northern Cascade Range [49,50]). Inland populations occur at relatively higher elevations; for example, western swordfern's range in Montana is from 3,500 to 5,000 feet (1,070-1,500 m) [126].
Western swordfern communities in the western hemlock zone are most common on lower slopes and flats such as toe slopes, benches, and stream terraces, although occurrence on steeper slopes at any aspect is possible. For example, the western hemlock-Port-Orford-cedar/western swordfern-redwood-sorrel community occurs mostly on flats but sometimes on slopes up to 35%, mostly with northern aspects [91]. In the western hemlock zone of the central western Cascade Range in Oregon, western swordfern communities tended to occur on slopes with north aspects, ranging from 18 to 45 degrees [222]. The western hemlock/western swordfern association in Mt Rainier National Park occurs mostly on low slopes or sloping benches with southerly aspects, but it can be found on slopes of 70% or more with any aspect [65]. Western swordfern was strongly correlated with aspect, favoring north- and east-facing slopes, in successional red alder stands in the Alsea River drainage of the Central Coast Ranges in western Oregon [29].
In redwood forests, western swordfern associations occur on both slopes and flats, and western swordfern cover may be greater near the coast than farther inland. In old-growth redwood stands in the Coast Ranges of northern California, western swordfern cover was greater on coastal sites than inland sites. Its cover was similar on slopes and flats near the coast, but it occurred only on flats inland [168]. Western swordfern occurred in all streamside redwood sites studied in northwestern California [179]. In southern Monterey County, the redwood/western swordfern-Pacific trillium ecological type occurs on mesic, moderate to very steep (50-100%), lower slopes. Most stands face north to north-northwest and are 50 to 175 feet (15-53 m) from the nearest stream [24].
Soils: Western swordfern grows on a variety of soils and parent materials including exposed bedrock, but the most luxuriant growth is found on deep, loamy soils, especially those developed on fluvial parent materials (e.g., [53,64,97]). Western swordfern is characteristic of moist but strongly drained, deep soils in northwestern Washington [75] and Canada [175], although western swordfern associations may indicate relatively shallow soils in some sites (e.g., [43,94,97]). Many western swordfern associations occur on moderately deep to deep (effective rooting depths of 3 feet (1 m) or more), well-drained but moist soils with fine to moderately fine (silty clay loam to sandy loam) surface textures [16,53,64,91,97,99,169]. Soils range from relatively stone free [53,94] to moderately stony (5-30% coarse fragments) or stonier [53,65,94]. Parent materials include alluvium, colluvium, outwash, and glacial till [53,97] derived from andesite, basalt, sandstone, siltstone, tuffs, breccias, lahar, or tephra deposits [53,65,95]. Western swordfern occurs only occasionally on rock [58], such as shaded talus slopes [183], cliffs, outcrops [98,192], and terraces adjacent to the ocean [19]. On Junipero Serra Peak in California, western swordfern occurred in Coulter pine and sugar pine stands on rock outcrops [200].
Western swordfern is nitrophytic [175] and grows best on nutrient-rich soils. It is a characteristic understory species on soils that are moderately to very rich in nutrients (e.g., [81,97,118,120,123,131,169,175]). Abundant and vigorous growth of western swordfern may indicate nutrient-rich sites [74]. In Canadian forests, presence of western swordfern indicates base-rich parent materials [175] or nitrogen-rich sites. It has greater frequency and cover on soils with relatively high pH and mineral nitrogen and relatively low carbon:nitrogen ratio [123].
Soils in western swordfern communities are often rich in organic matter (e.g., [94]), and western swordfern can grow on decaying stumps [115]. In redwood/western swordfern forests, soils are Ultisols; base saturation is low, but organic matter content is high [66]. In cool mesothermal forests in southern British Columbia, western swordfern occurs on a variety of organic substrates, but it is an indicator of moder and mull humus forms [123,175], which are differentiated by a layer of organic materials with more than 17% organic carbon overlying mineral soil [121]. A comparison of vegetation on stumps and on the ground in coniferous (Douglas-fir-western hemlock-western redcedar) and deciduous (red alder) forest sites in Olympia, Washington, showed that western swordfern had similar stem density in each forest type, and had higher stem density on ground microsites in both forests (P<0.005). It sometimes occurred on stumps in the deciduous forest, but not in the coniferous forest [115].
Moisture relationships: Western swordfern associations are characteristically found in moist or shaded locations, where drainage is good but little moisture stress is encountered. In western hemlock forests, western swordfern is most often dominant in moist and wet communities [53] (e.g., see Table 3). For example, the western hemlock/western swordfern-redwood-sorrel association typically occurs on very moist streamside slopes, and the western hemlock/western swordfern association occupies toe slopes and northern aspects [64]. On the Olympic National Forest, the Sitka spruce/western swordfern-redwood-sorrel association occurs along toe slopes or in areas of high precipitation, high humidity, or fog [97]. The western hemlock/Pacific rhododendron/western swordfern association on the Siuslaw National Forest is the moistest of the Pacific rhododendron associations [94].
Table 3. Examples of western swordfern associations in the western hemlock forest zone on the Gifford Pinchot National Forest on a moisture gradient from wet to dry (Topik and others 1986 as cited by [181]) Wet group Moist group Mesic group Dry group devils club-western swordfernwestern swordfern-redwood-sorrel
western swordfern
dwarf Oregon-grape-western swordfern -none-The 2 most important understory or groundlayer species in western hemlock and Douglas-fir forests are western swordfern on relatively moist sites and salal on slightly drier sites [16,41,62,63]. In Douglas-fir/western hemlock forests in the eastern portion of the Olympic Peninsula, for example, forest understories are dominated by dense salal on the drier west- and south-facing slopes, and by western swordfern, twinflower, oneleaf foamflower, and northwestern twayblade on north- and east-facing slopes [64]. Western swordfern and salal may codominate on intermediate, mesic sites [64,150]. On alluvial landforms of the McKenzie River valley, Oregon, 2 topoedaphic climaxes were identified. Understories were dominated by western swordfern and redwood-sorrel on terraces with fine, sandy loam to silt loam soils derived from silty river alluvium; and by dwarf Oregon-grape and salal on rockier soils with coarser alluvium or glacial outwash. Sites with finer-textured soils had greater late summer moisture availability [89]. Western swordfern is an indicator of relatively cool, moist sites in Douglas-fir forests on the HJ Andrews Experimental Forest, Oregon [139], and in tanoak-redwood and tanoak-vine maple associations in southwestern Oregon [13,14].
In British Columbia, western swordfern is most abundant in ecosystem associations with moderately well-drained to poorly drained soils [118,140]. Western swordfern is sporadic to scattered on water-shedding sites, and plentiful to dominant on water-receiving and colluvial sites enriched by surface flow of fine organic materials [121]. In the coastal Douglas-fir zone of southern Vancouver Island, where summer moisture deficits are common, western swordfern occurs only where seepage water augments soil moisture supply. In wetter climates it is less restricted by soil moisture [74].
In drier forest zones, western swordfern presence or abundance may indicate relatively moist sites. In the Willamette Valley, the Oregon white oak/California hazelnut/western swordfern forest community was the most mesic and occurred on moderate to steep, sheltered slopes. Western swordfern cover averaged 34% but reached 80% with fronds >3 feet (1 m) tall on the best sites. In progressively drier communities, frequency, cover, and height of western swordfern declined (Table 4), and in the Pacific poison-oak community it grew "only as a sporadically distributed, depauperate plant" [203].
Table 4. Western swordfern cover and frequency (%) in Oregon white oak plant communities listed from mesic to xeric [203] California hazelnut/western swordfern sweet cherry/common snowberry Saskatoon serviceberry/common snowberry Cover Frequency Cover Frequency Cover Frequency 34 61 13 29 4 9In the Selway-Bitterroot Wilderness in Idaho, western swordfern is a common understory species in "older-aged" grand fir-western redcedar forests on creek bottoms and smaller stream ravines [73].
Plant communities: Western swordfern is widespread, abundant, and often an understory dominant in the maritime forests along the northern Pacific coastline; it also occurs in some inland forest types. Maritime forests occur between the ocean shore and the crest of the Coast Ranges and are variously dominated by western hemlock, Sitka spruce, redwood, western redcedar, and Douglas-fir [62,136]. It is an understory dominant in some Port-Orford-cedar, Pacific silver fir, Oregon white oak, and tanoak communities, and it often occurs in the understory of successional red alder communities. Western swordfern also occurs in drier forest zones, and at higher elevations near the Pacific Coast but is less often an understory dominant [62].
Information compiled from vegetation classification literature from Oregon and Washington shows the average cover and frequency of western swordfern in plant communities in each of 5 forest zones (Table 5). Western swordfern is most common in the western hemlock zone, where it is most prominent in communities on cold, wet sites. It is well suited to the moist and wet climates in the Pacific silver fir zone but uncommon in the drier sites of that zone. Western swordfern is present in the warmer-drier Douglas-fir zone, but cover is low. It is infrequent in the mountain hemlock zone and absent or rare in the subalpine fir zone [181].vine maple-salal
93 15 Pacific rhododendron-western swordfern 82 22 Pacific rhododendron-dwarf Oregon-grape 70 10 Pacific rhododendron-salal 60 7 Pacific rhododendron 82 9 salal-evergreen huckleberry 100 4 evergreen huckleberry 100 43 salal-dwarf Oregon-grape 84 11 Douglas-fir zone salal 78 3 salal-creambush oceanspray 85 2 creambush oceanspray-dwarf Oregon-grape 78 2 creambush oceanspray-baldhip rose 76 3 *no dataWestern hemlock zone forests: The regional climatic climax for the western hemlock zone in the Oregon Coast Ranges is thought to be the western hemlock/western swordfern association [64]. Shrub layers are not well developed in these habitats, although vine maple or dwarf Oregon-grape may dominate. Lush herbaceous understories are common in western hemlock/western swordfern habitats. Foamflowers, twinflower, deer fern, lady fern, and several lilies are among the numerous succulent herbs that cover the forest floor in these rich habitats [62]. See Appendix B for a list of western swordfern associations that occur in western hemlock forests and are described in regional vegetation classifications.
Sitka spruce zone forests: Western swordfern is a common understory species in the long, narrow Sitka spruce zone along the Pacific coastline from southeastern Alaska to southern Oregon. Coniferous forest stands in this zone are typically dense, tall, and among the most productive in the world. Western hemlock-Sitka spruce forests are mostly restricted to a narrow coastal band but may occur as much as 50 miles (80 km) inland on cool, moist slopes, along stream bottoms, and around lake margins where fog is prevalent during the growing season. Western swordfern, redwood-sorrel, and red huckleberry are common in these optimum conditions [64]. Western swordfern and redwood-sorrel are the most important understory species in old-growth forests dominated by Sitka spruce and western hemlock in the very heavy rainfall area on the western slopes of the Olympic Mountains. These forests have distinctive characteristics including massive trees, numerous canopy levels, evergreen dominants, a profusion of epiphytes, an abundance of bigleaf maple and vine maple, abundant nurse logs, and "an intangible overall quality of growth" [64]. See Appendix B for a listing of Sitka spruce/western swordfern associations described in regional vegetation classifications.
Western swordfern is less common in Alaska and was mentioned in only a few vegetation classification publications from there. Details were lacking in all but one of these. In the Stikine area of Southeast Alaska it occurred at low frequency and cover in closed-canopy forests (60-100% canopy cover) dominated by western hemlock, Sitka spruce and/or western redcedar, and in open-canopy (25-59% canopy cover) western hemlock forests. Its greatest frequency was in western hemlock/blueberry/spreading woodfern communities (22%), where its cover ranged from 1% to 6%; and in Sitka spruce-western hemlock/American skunkcabbage/sphagnum communities (33%), where its cover ranged from 3% to 10% [145].
Pacific silver fir forests: Western swordfern is an understory dominant in Pacific silver fir forests on the Olympic Peninsula (see Appendix B). In the Cascade Range of Oregon and southern Washington, western swordfern occurs on warm sites in the Pacific silver fir series [26,93] but typically has low cover (about 1-2%) [53,93].
Redwood forests: Redwood forests occur in a narrow strip from southwestern Oregon to Santa Cruz and are characterized by pure stands of redwood on floodplains and with a mixed lower tree stratum on hillsides. Western swordfern is one of the most abundant plants in redwood forests [20,25,41,205], especially in old-growth stands [21,23] on moist sites [64] such as alluvial flats and lower slopes [63]. See Appendix B for a list of redwood/western swordfern associations. Figure 3. Western swordfern growing under towering redwoods on the Simpson Reed Grove Trail, Redwood National Park. Photo courtesy of the National Park Service, www.nps.govTanoak forest: Western swordfern is among the most common ferns in the tanoak series of the Siskiyou Region of southwestern Oregon. It is most abundant in coastal associations such as tanoak-coast redwood and tanoak-vine maple [13,14] (Appendix B).
Other community types: Western swordfern may be an understory dominant or indicator species in Oregon white oak, canyon live oak, and coyotebrush communities. The Oregon white oak/California hazelnut/western swordfern association occurs on moist sites in the Willamette Valley, Oregon [194,203], and western swordfern was characteristic of the Oregon white oak/common snowberry woodland type in the Bald Hills oak woodlands in Redwood National Park, California [197]. A coyotebrush/western swordfern association is described in California northern coastal sage scrub [20]. A Douglas-fir/canyon live oak/western swordfern association was described in the northern Sierra Nevada [57], and western swordfern occurs with low cover in mature canyon live oak forest on the San Bernardino National Forest in southern California [156].
Riparian: Western swordfern is a common to dominant species in many riparian communities throughout its range. It is a characteristic species in widespread and highly productive black cottonwood-willow riparian forests occurring on bottomlands, riverbars, streambanks, and meadows along the Pacific coast [45]; and in black cottonwood riparian forests in bottomlands, floodplains, gravelbars, and banks of perennial streams in northern coastal California [101]. In northwestern Oregon, western swordfern occurs in several plant communities on cobble bars and low floodplains, and may reach 17% to 25% cover in some, though it is not a named community dominant. Western swordfern also occurs in swamp communities, such as the red alder/slough sedge-American skunk cabbage community, where it may be abundant on logs and stumps and reach 45% cover [143]. In California, western swordfern is common in riparian forests dominated by Port-Orford-cedar in ravines and draws, along streams, and on mesic, protected slopes with a strong maritime influence [20].
Inland areas:
Eastern Washington and Oregon: Western swordfern is rare in eastern Washington and Oregon, though it occurs as an understory dominant in the relatively warm, moist grand fir series in the Blue Mountains [2] with wild ginger and oak fern [110]. A grand fir/western swordfern-wild ginger potential vegetation type occurs on cool, very moist site types [171]. These communities typically occur on lower slopes or riparian areas and may exist as residual stringers that do not burn as often as associated uplands [2].
Western swordfern is classified as a facultative wetland species in eastern Washington, where it occurs in several riparian and wetland communities with low cover, including those in the Pacific silver fir, western hemlock, and black cottonwood series [125]. It also occurs in small amounts in old-growth western redcedar-western hemlock forest [130], Pacific ponderosa pine (hereafter, ponderosa pine) communities, the grand fir-Oregon boxwood association, the western hemlock-Oregon boxwood association, and the western redcedar-devil's-club association [42].
Idaho: Western swordfern is not widespread in Idaho but is most abundant in western redcedar [37,163], grand fir [37,56,163], and western hemlock communities [163]. It may also occur in riparian habitats [84]. In northern Idaho, western swordfern dominated the diverse understory in a western redcedar/northern maidenhair habitat type along Nylon Creek north of Dworshak Reservoir. Western swordfern commonly occurs in the western redcedar/wild ginger habitat type and may occasionally dominate the forb layer in the grand fir/wild ginger habitat type [37]. Western swordfern occurred with low cover at all stages of succession in the Rocky Mountain juniper/red-osier dogwood habitat type in eastern and southern Idaho [84].
Montana: Western swordfern is rare in Montana. It was recorded in late-seral to climax stands of the western hemlock/oak fern habitat type with an average cover of 1% [85]. Populations have been recorded in the Bitterroot and Sapphire ranges; a population at Charles Waters Memorial Campground was extirpated by collectors [126].
South Dakota: According to a flora published in 1977 [48], western swordfern occurred in moist places in the Black Hills. However, it was listed among the rare plants of South Dakota in 1985, with its status "undetermined" and this comment: "Recently reported but population has apparently been extirpated" [104].
See Appendix B for a list of western swordfern association described in vegetation classifications, or the Fire Regime Table for a list of plant communities in which western swordfern may occur and information on the FIRE REGIMES associated with those communities.Western swordfern is typically present during most stages of stand development [144]. It can establish in primary succession, such as after deglaciation or volcanic eruption, and in early secondary succession, but typically reaches its best growth and greatest abundance in mid- to late-successional forests [181].
Figure 7. Western swordfern reflecting lightspots in the forest understory. Photo courtesy of Hansen's Northwest Native Plant Database, http://www.nwplants.com.Shade tolerance: Western swordfern has a high tolerance for shade but can also grow in the open [35,95,100]. Western swordfern communities often occur in the understory of closed-canopy forests, but western swordfern plants can persist following canopy-opening disturbances [175]. Some authors have noted that western swordfern may have lower cover in dense shade and grows best in "lightspots" under dense canopies [16,192]. Carey [28] notes that western swordfern grows rapidly when forest canopies are even moderately open and forms dense carpets that can shade out other plants.
Although it tolerates a wide range of light conditions, western swordfern seems to have optimal growth under relatively low light conditions, and its response to increased light depends a lot on site moisture availability. In the coastal redwood region, western swordfern's optimum light requirement (where it reached its highest cover at about 2%) was less than 3%, but it grew in areas having up to 40% of full sunlight [217]. Many examples in the literature demonstrate that western swordfern persists after canopy-opening disturbances (see Secondary succession); however, its abundance and vigor may depend on site conditions and disturbance severity (i.e., moisture availability, size and pattern of canopy openings, and degree of soil disturbance). In clearcut areas, for example, western swordfern often prefers protected, shaded locations. This probably reflects sensitivity to high evoptranspirative losses rather than intolerance of light itself [74], and it may be more pronounced in clearcuts on south-facing slopes (e.g., [68]). When plants of western swordfern are subjected to increased insolation through removal of overstory shade, the fronds can become dwarfed and more erect, and the pinnae become crisped [74,181] (see Botanical Description).
Western swordfern communities commonly occur in the understory of old-growth and late-successional forests, indicating shade tolerance of the species. Stands typical of the western hemlock/western swordfern association in the western Cascade Range, Oregon, have a relatively dense overstory averaging 70% to 80% canopy cover [53,64]. In the western hemlock zone of the central western Cascade Range, western swordfern communities tended to occur on sites with >100% cover of mature trees [222]. In a Douglas-fir/vine maple/western swordfern community at Monument Peak, Oregon, "only the most shade-tolerant species", such as western swordfern or mosses, grew under the dense vine maple canopy [6]. In 4 redwood stands studied at Humboldt Redwoods State Park, California, western swordfern and redwood-sorrel dominated the forest floor on 2 well shaded lowland sites that had only occasional sunlight breaks [177].
On the southeastern Olympic Peninsula, the western hemlock/salal/western swordfern association occurs in matrix forests among anthropogenically fire-maintained beargrass savannas that have grown into forests with fire exclusion. Former savanna plots have some western swordfern, but western swordfern is less abundant than in the forest matrix [167], suggesting that it spreads into the savanna slowly, after trees establish.
Primary succession: During primary succession on the foreland of Coleman Glacier on Mt Baker in northwestern Washington, western swordfern was uncommon but was most prevalent about 95 to 180 years after deglaciation. Vegetation in this age class had the highest tree canopy cover and was dominated by Pacific silver fir and western hemlock. Soils were volcanic ash and colluvium over glacial till; under forest canopies, the mineral soil was covered by an organic horizon up to 12 inches (30 cm) thick [111].
Table 7. Average cover of western swordfern during primary succession on the foreland of Colman Glacier in northwestern Washington [111]. Approximate time since deglaciation (years) 0-24 70-95 95-180 300 Mean western swordfern cover (%) 0 0.32 2.93 0.54In a study comparing primary successional uplands to refugia (habitats where plants survived as rootstock) after the 1981 eruption of Mt Saint Helens, plants in the blast zone were inventoried in the summers of 1993 and 1994. Before the eruption vegetation in the area was a patchwork of forested and clearcut areas, typical of the Pacific silver fir zone in Washington. After the eruption, wind-dispersed invasive species dominated. Western swordfern was infrequent to common throughout the area in both primary successional habitat and refugia [207].
Secondary succession: Western swordfern associations occur in late-successional and old-growth forests with natural disturbance regimes typified by very infrequent large-scale and infrequent small-scale disturbances. The most common contemporary disturbances in many western swordfern habitats are logging and associated slash disposal and site preparation. The impact of these and other disturbances on western swordfern populations depends on light and moisture conditions in the postdisturbance understory environment. Reviews suggest its response to logging is variable, although western swordfern generally persists, and no studies report dramatic postlogging increases or decreases of its abundance or cover. Western swordfern probably maintains or increases its cover and vigor only on microsites without severe soil disturbance or significant summer moisture stress (reviews by [35,74]). In the absence of severe soil disturbance, western swordfern usually persists or reestablishes from surviving rhizomes following overstory mortality at most scales. Exceptions may be found on exposed and/or dry sites where moisture stress is severe [74] and at the extremes of its range, where sites may already be marginal for western swordfern and become less habitable with soil and canopy disturbance.
The following summary of the literature describes western swordfern's role in secondary succession following canopy opening disturbances and is organized by forest type. It includes several studies where vegetation response was monitored after canopy removal, almost entirely after logging, especially clearcutting, as well as general descriptions of secondary succession, such as those found in vegetation classifications that do not usually specify disturbance type, stating only, "after fire or logging". Specific examples of western swordfern response to fire and examples of successional changes in western swordfern communities following wildfires or prescribed fires other than slash burning are included in the discussion on Fire Effects and Management.
Western hemlock and Douglas-fir forests: Western swordfern is a common dominant in old-growth forests in the western hemlock zone. Prior to European settlement, these forests were mostly late successional and old growth with very large trees, dense canopies, infrequent, small-scale disturbances from windfall, insects, or disease; and less frequent, larger disturbances from landslides, blowdown, fluvial action, and fire. Although changes of ground cover in old-growth stands are relatively slow, they are constantly taking place. Understory and ground layer plants respond to canopy gaps in various ways; western swordfern response depends largely on moisture conditions [69].
Lush growth of western swordfern may indicate late-successional, old-growth, or relatively undisturbed sites. The regional "climatic climax" for the western hemlock zone in the Oregon Coast Ranges is thought to be the western hemlock/western swordfern association [64]. Stands typical of the western hemlock/western swordfern association in the western Cascade Range, Oregon, are generally made up of old-growth Douglas-fir and western hemlock; western swordfern is the only constant herbaceous species, with an average cover of 25% [53,64]. In the western hemlock zone of the Gifford Pinchot National Forest, Washington, old-growth stands of the western hemlock/western swordfern-redwood-sorrel association have huge, widely-spaced Douglas-firs, western hemlocks, and western redcedars towering over a lush carpet of redwood-sorrel interspersed with western swordfern [208]. Other old-growth types include the western hemlock/western swordfern-threeleaf foamflower association in the northern Cascade Range [159] and Olympic Peninsula; and the western hemlock/salal-western swordfern association on the Olympic Peninsula [159,166]. The western redcedar-Douglas-fir-western hemlock/western swordfern-spreading woodfern community is a late-successional community that develops in forests with infrequent stand-replacing fires (~150-200 years) and occasional mortality from windthrow, insects, or disease (leading to gap dynamics and multiage structure) in coastal British Columbia [157]. The Oregon white oak/California hazelnut/western swordfern community occurs on the least disturbed sites in the Willamette Valley [203], and the western redcedar-grand fir/western swordfern community occurs in undisturbed locations on the moistest sites in interior valleys of the San Juan Islands, whereas areas disturbed by logging commonly support red alder communities [64]. See Table 2 for western swordfern cover and site characteristics in remnant old-growth forests in the northern Coast Range of Oregon [70], and Appendix B for more examples of late-successional western hemlock communities in which western swordfern is a dominant species.
Western swordfern occurs in Douglas-fir forests on Mount St Helens [147]. Following the 1980 eruption, it was associated with scorched forest but not with clearcut or blowdown forest [79]. It occurred in the habitats with the greatest plant cover, usually in organic soil such as the area around a stump base [80]. The maximum tephra depth from which western swordfern was excavated was 3.5 inches (9 cm), 13 to 15 months after the eruption. The authors concluded that western swordfern rarely produces buds in tephra [8]. Most of the area was salvage logged between 1982 and 1984, then planted with noble fir. Western swordfern presence and abundance corresponded with litter depth and downed woody debris, which were greater on unsalvaged plots. In July of 2003 western swordfern cover and frequency averaged 0.05% and 28%, respectively, on salvage logged sites, compared with 0.4% and 80% on unlogged sites [206].
Postlogging succession: Because much of the western hemlock zone in the Pacific Northwest [64] and the majority of forests in the coastal Douglas-fir zone in British Columbia [161] have been logged during the last 2 centuries, much of the information available on succession in these communities comes from studies of plant community changes after logging and site preparation. The remainder of this subsection includes information from such studies as it may pertain to postfire succession. Timber harvesting operations in the western hemlock zone historically involved clearcut logging followed by slash burning under prescribed conditions to reduce fire hazard, prepare the seedbed for planting, and reduce shrub cover [153]. According to Garrison and Smith [67], western swordfern is among the species in Douglas-fir forests of Oregon and Washington that "suffer the most loss in crown cover" from the accumulation of heavy slash and soil disturbance after clearcutting. Burning of logging waste causes additional changes [67]. Although its abundance may be reduced initially, on sites where moisture is not limiting western swordfern recovers in early succession, and it may be an understory dominant or codominant in seral stands that develop after logging disturbances [64]. For example, Douglas-fir/western swordfern and red alder/western swordfern community types are considered relatively young stands in the western hemlock/western swordfern association in Mt Rainier National Park [65].
Western swordfern occurs throughout postharvest succession in western hemlock and Douglas-fir forests, but it is generally most abundant in middle to late succession [17,18,46,122,160], with the exception of dense, closed-canopy stands, where its abundance drops off and it most frequently occurs in light spots (see Shade tolerance).
Post-harvest succession and the abundance of western swordfern follow some general patterns in the western hemlock forest zone, but vary depending largely on predisturbance community composition, site characteristics (especially available moisture), and disturbance type, timing, and severity, including postharvest site preparation. The general sequence begins with an herbaceous stage dominated by nonresident annual and perennial herbs, which typically lasts 4 or 5 years; residual herbs, such as western swordfern, may contribute substantial cover during this stage. A shrub stage follows, as residual shrubs develop in canopy openings, and continues until the shrubs are overtopped by tree saplings, after about 10 to 25 years [62].
On sites with greater available moisture, western swordfern recovers more rapidly [39,52], and red alder is likely to dominate early forest succession [39,62]. In the Oregon Coast Ranges, herbaceous species surviving from the predisturbance stand, especially western swordfern, often constitute an important component of the early-seral vegetation following logging; however, residual species such as western swordfern, broadleaf starflower, and redwood-sorrel are reported to be of only minor importance during the first 10 to 25 years of succession in the relatively drier Cascade Range (review by [64]). On relatively xeric sites in the HJ Andrews Experimental Forest in the western Cascade Range of Oregon, western swordfern cover was reduced by at least half in the first year [68] and maintained very low cover for at least 10 years after clearcutting and slashburning. The author suggested that western swordfern "apparently found survival difficult or impossible under clearcut conditions" on the steep, south-facing slopes in the study area [69]. Following the period of shrub dominance, stands may go through a red alder stage on moist, productive sites such as western swordfern habitats [62]. Red alder is among the first trees to establish on moist sites, and pure stands are common in the Oregon and Washington coastal mountains and parts of the Puget Sound region. Red alder is gradually replaced by Douglas-fir and western hemlock but may dominate for up to 90 years [39].
Western swordfern communities tended to have greater resilience than other community types in the HJ Andrews Experimental Forest. A series of studies used long-term sampling of permanent plots before and after clearcutting and slash burning in 100- to 500-year-old Douglas-fir forest [52,77,78]. Initial understory in the western swordfern community was richer and more structurally complex than in most other communities, and surviving perennial herbs and shrubs were abundant, resulting in relatively rapid community recovery. The resilience of the western swordfern community was attributed to the ability of dominant herb and shrub species to sprout from subterranean structures following slash burning, and western swordfern "regenerated continuously from surviving rhizomes or stem bases" [77,78]. Abundance of understory dominants, including western swordfern, was reduced during the first 2 years after slash burning, when wind-dispersed annuals such as tall annual willowherb and nonnative woodland ragwort dominated. This was followed by increases of initially subordinate (e.g., sweetscented bedstraw) and dominant (e.g., western swordfern) forest herbs. Shrubs began to dominate 14 years after disturbance. Trees did not dominate until after 20 years [52,78]. See the Research Project Summary of these studies for more information.
Western swordfern response varies with timing and severity of disturbance during logging and especially site preparation [52,78]. Techniques that remove the plant from the ground can nearly eliminate the species from the site. Brush bale scarification totally eliminated western swordfern from a study site in Oregon; scarification of several sites near Vancouver left western swordfern only on undisturbed microsites [35]. In a comparison of the effects of chemical, fire, and mechanical site preparation in an area that was repeatedly logged, western swordfern frequency was similar among all but scarified sites, where soil was severely disturbed, and western swordfern was reduced from about 25% to 0% frequency [114].
Slash burning may alter succession and decrease western swordfern abundance compared to unburned, logged sites (e.g., [16,152,182]). Some authors note that western swordfern was initially reduced or eliminated on slash-burned sites compared to unburned sites [107,152,199]. Although western swordfern can survive severe fire, plants may be restricted to unburned patches and aboveground structures may be absent for several years following slash burning (reviews [35,74]). Western swordfern abundance may remain low and even decline as succession proceeds on slash-burned sites exposed to intense insolation, low humidity, and low soil moisture (e.g., [69,107,116]). If left unburned, residual species such as western swordfern can dominate early succession; if slash is burned, native and nonnative annual herbaceous species that establish from windborne or soil-banked seed, tend to dominate. In areas where mineral soil is exposed by logging activities, successional patterns may resemble those on burned sites [39].
Sitka spruce forests: Western swordfern is a common dominant in old-growth forests in the Sitka spruce zone of North America (for examples, see Table 2 and Appendix B). Old-growth Sitka spruce associations include the Sitka spruce/western swordfern association [159,166] and the Sitka spruce/western swordfern-redwood-sorrel association [97] on the Olympic Peninsula, and the Sitka spruce/western swordfern association in coastal British Columbia [124]. Areas typical of the Sitka spruce/western swordfern-redwood-sorrel association on the Olympic Peninsula have burned very seldom in the last 500 years [97]. Western swordfern was present in late-successional forest dominated by western hemlock, Sitka spruce, and western redcedar in Southeast Alaska, but was not mentioned as an important species in second-growth forests [201].
Early successional trends following fire or logging in the Sitka spruce zone are similar to those in the western hemlock zone, although dense shrub communities are more common in the Sitka spruce zone because of more favorable growing conditions [62,64], and young stands in the Sitka spruce zone are more likely to be dominated by western hemlock and Sitka spruce than by Douglas-fir. Red alder is also more abundant after logging in the Sitka spruce zone due to the preponderance of moist and wet sites [29,62]. Shrub communities can develop quickly after canopy-opening disturbances in these forests [62,64]. Several of these seral communities have been described and mapped along the northern Oregon coast, including the salmonberry-western swordfern, vine maple-western swordfern, and salal-red huckleberry types [64]. In many cases, western swordfern is the major early-seral understory species after clearcutting in the Sitka spruce/western swordfern association on the Siuslaw National Forest; these sites are generally resilient to fire effects (review by [94]).
Western swordfern is usually present even in young stands of the Sitka spruce/western swordfern-redwood-sorrel association on the Olympic Peninsula, and it is often conspicuous by the time of crown closure (about 15 years). Western swordfern abundance becomes relatively stable by about 100 years [97]. A chronosequence study on the Olympic Peninsula in the Sitka spruce-western hemlock zone showed that western swordfern had high frequency (50%-67%) but low cover (0.7%-6.25%) in all age classes from 0 to >199 years. Percent cover of western swordfern increased steadily with forest age, but differences were not significant among age classes (P>0.05) [212].
Redwood forests: Western swordfern occurs throughout succession in redwood forests but may be more abundant in second-growth stands. In Redwoods State Park, the redwood-Sitka spruce/evergreen huckleberry-western swordfern and Sitka spruce/western swordfern-salmonberry associations occur in cutover forests [142]. Riparian forests in adjacent watersheds at Redwood National Park were studied to understand structural and compositional differences between old-growth and unmanaged second-growth forests about 40 to 50 years old. Old growth was dominated by redwood, and second growth was dominated by red alder, Douglas-fir, and redwood. Western swordfern, deer fern, and lady fern dominated the understory in both old-growth and second-growth forests. Western swordfern had the highest importance value and the highest relative cover of all understory plants for both old-growth and second-growth stands, 52.3% and 71.2%, respectively [202]. Loya and Jules [138] identified 4 stages of postlogging development in redwood forests: initiation, closure, mature, and old growth; western swordfern was an indicator of the closure stage [138]. Similarly, western swordfern was associated more with recently harvested sites than sites with longer times since harvest (P<0.05) in riparian redwood forests ranging from 10 to 110 years since harvest. In 0- to 30-year-old forests, overstory canopy cover was about 35%, and in >100-year-old forests, canopy cover was about 70% [178]. Ten years after logging in redwood forests in the Santa Cruz Mountains, western swordfern was commonly found in canopy gaps created by logging [22].
Red alder forests: Seral stands dominated by red alder, particularly those with western swordfern dominating the herb layer, are most common in wetter parts of the western hemlock zone, (i.e., the northern Washington Cascade Range, the west side of the Olympic Mountains, and in the Coast Ranges) and in the Sitka spruce zone. Understory vegetation in red alder stands is most frequently dominated by salmonberry in the shrub layer and western swordfern in the herb layer [64]. As the short-lived red alder dies, many of these stands may become dominated by a dense cover of salmonberry and western swordfern that can persist and slow establishment of conifers (review by [40]).
Western swordfern occurs throughout succession in red alder stands but tends to increase with stand age and reach its greatest abundance in middle to late succession. In the Alsea River drainage of the central Coast Ranges in western Oregon, Carlton [29] studied 44 red alder stands ranging in age from 7 to 87 years, and originating from different types of disturbance: mostly logging, but also fire, slides, debris flows, and unstable ravel soils. Western swordfern was most abundant in middle age classes and still a prominent component of older stands, along with salmonberry and vine maple. Five understory communities were identified in these red alder stands: 1) a western swordfern community was most characteristic of young red alder stands but also occurred under dense, middle-aged stands on moderate to steep slopes with low light levels in the understory; 2) a western swordfern-mixed shrub community occurred under middle-aged red alder stands; 3) a western swordfern-salmonberry community occurred in many middle-aged red alder stands; 4) a salmonberry community occurred on flat terraces or stream bottoms under middle-aged stands where western swordfern was present but much less abundant; and 5) a vine maple community where western swordfern was a codominant under most stands of old, senescing and several middle-aged red alder stands. None of the communities was restricted to only one age class of red alder [29]. Fifteen red alder stands on river-bottom, alluvial soils in the Oregon Coast Ranges, ranging in age from 2 to 64 years, were evaluated between 1 August and 7 September 1969. Succession in the understory proceeded from a grass-herb to shrub-fern understory over a 60- to 70-year period. Western swordfern crown cover and frequency generally increased with stand age and were highest in stands aged 39 to 64 years, with cover ranging from 4% to 37% and frequency ranging from 18% to 92%. In stands younger than 35 years, cover ranged from trace to 4% and frequency from 4% to 22% [96]. On steep terrain in the western hemlock zone of the central Oregon Coast Range, a debris flow deposited material containing western swordfern rhizomes onto the valley floor of a second order stream watershed. Western swordfern reproduced from rhizomes and increased rapidly. Its abundance increased steadily over time, from 4% frequency the first growing season after the deposition to 30% 9 years later [162].
Floodplains and river terraces: Western swordfern communities often indicate later stages of succession on floodplains and river terraces in the Pacific Northwest. The California bay-Douglas-fir/vine maple/western swordfern community in the Umpqua River valley in the Oregon Coast Ranges is an old-growth association on the highest floodplain terrace [204]. A riparian chronosequence spanning more than 3 centuries along the Queets River, Olympic National Park, showed that the western swordfern/redwood-sorrel plant community occurred on the oldest sites in the study area (60-330 years old), on soils with relatively finer surface textures (38%-57% silt and clay), and on the highest terraces (6.2-8.5 feet (1.9-2.6 m)) above the low flow channel, mostly above the reach of annual floods [215]. In 29 plots on floodplains of 2 rivers on the west coast of Vancouver Island, western swordfern was among the species "typical of rich climax ecosystems". Western swordfern was absent from the pioneer seral stage, averaged 12% cover in the young seral stage, and 23.5% cover in the mature climax stage of floodplain succession. The climax stage was dominated by Sitka spruce with an understory of salmonberry, coastal hedgenettle, threeleaf foamflower, and western swordfern [34].
On alluvial landforms of the McKenzie River Valley, Oregon, 2 topoedaphic climaxes were identified: the western hemlock/western swordfern-redwood-sorrel association on terraces with fine, sandy loam to silt loam soils derived from silty river alluvium; and the western hemlock/dwarf Oregon-grape-salal association occurring on rockier soils with coarser alluvium or glacial outwash. Three early seral communities (willow, red alder, and black cottonwood) were identified (Table 8). Western swordfern established during the red alder seral stage on relatively fine-textured soils. Dominants in the herb layer of the black cottonwood association include western swordfern and several other herbaceous species common to the grand fir association. Western swordfern reached its highest cover in the Douglas-fir/beaked hazelnut/western swordfern association; however, individuals were chlorotic and thin-leaved compared to those growing in stands of the western hemlock/western swordfern-redwood-sorrel association. The western hemlock/western swordfern-redwood-sorrel association was the most extensive in the area [89].
Table 8. Western swordfern cover and frequency in successional communities on alluvial landforms in the McKenzie River Valley, Oregon [89]. Plant community dominants Site characteristics Cover (%) Frequency (%) willow recent alluvium no data no data red alder Establishes following deposition of 20-30 cm gravelly sand, which increases terrace elevation; red alder is typically replaced within 30 to 50 years 1 40 black cottonwood If little elevation of the floodplain occurs (through either sedimentation or downcutting of the river), black cottonwood replaces red alder no data no data grand fir Replaces red alder in areas with deeper fine sediment deposits, usually within 30 to 70 years 15 100 western hemlock/western swordfern-redwood-sorrel Stands were 200-500 years old; most areas of this association had probably been through one or more fires 22 100 Douglas-fir/California hazelnut/western swordfern Develops on sites that have burned within the last 100 to 200 years 26 100 Western hemlock/dwarf Oregon grape-salal Develops on shallow to moderate cobbly loams to cobbly sandy loams on terraces and glacial outwash plains, at about 450-500 years no data no data Douglas-fir/dwarf Oregon-grape-salal Develops on shallow to moderate cobbly loams to cobbly sandy loams on terraces and glacial outwash plains 1 36Fonda [59] described 5 plant communities along the Hoh River in Olympic National Park, (Table 9). Western swordfern occurred in all of these communities and was most abundant in 400- to 750-year-old communities on 1st and 2nd terraces and rockslides. This study also describes soil characteristics for each community, noting a strong relationship between terrace age, soil moisture, and soil profile development. The younger land surfaces are substantially drier than the older terrace, which may affect western swordfern abundance [59].
Table 9. Western swordfern cover and frequency in 5 plant communities representing 5 successional stages along the Hoh River in Olympic National Park [59] Plant community Location Stand age (years) Cover (%) Frequency (%) red alder-Scouler willow gravel bars 80-100 1.5 40 Sitka spruce-bigleaf maple-black cottonwood 1st terraces 400 22.3 88 bigleaf maple rockslides where 2nd terrace meets valley wall <750 19.0 100 Sitka spruce-western hemlock 2nd terraces 750 22.4 76 western hemlock 3rd terraces >750 2.6 30The scientific name of western swordfern is Polystichum munitum (Kaufl.) Presl (Dryopteridaceae) [36,48,58,98,100,106,112,126,170,183].
Western swordfern is closely related to Polystichum imbricans based on morphologic [216] and electrophoretic [191] analysis.
Hybrids: Hybridization and polyploidy have contributed to morphological diversity and taxonomic complexity in the widespread genus Polystichum [190]. At least 1 or 2 hybrid plants are expected in large, mixed Polystichum populations, and several sterile interspecific hybrids have been reported. Hybrids between western swordfern and P. andersonii, P. californicum, P. scopulinum, P. braunii, P. kruckebergii, P. dudleyi, and P. lemmonii have been reported (review by [58]). According to Hickman [98], hybrids with P. dudleyi are called P. californicum. Polystichum munitum × P. andersonii and P. munitum × P. lemmonii hybrids are described by Soltis and others [190].
Polystichum munitum, the western swordfern,[1] is an evergreen perennial fern native to western North America, where it is one of the most abundant ferns in forested areas. It occurs along the Pacific coast from southeastern Alaska to southern California, and also inland east to southeastern British Columbia, northern Idaho and western Montana, with disjunctive populations in northern British Columbia, Canada; the Black Hills in South Dakota, United States; and Guadalupe Island off of Baja California, Mexico. Western swordfern is known to have locally naturalized in parts of Great Britain and Ireland.[2]
The dark green fronds of this fern grow 50 to 180 centimetres (1.6 to 5.9 ft) tall, in a tight clump spreading out radially from a round base. They are single-pinnate, with the pinnae alternating on the stalk. Each pinna is 1 to 15 centimetres (0.39 to 5.91 in) long, with a small upward-pointing lobe (a sword hilt, hence the name) at the base, and the edges are serrated with bristly tips. Individual fronds live for 1.5 to 2.5 years and remain attached to the rhizome after withering. The round sori occupy two rows on either side of the midrib of each pinna and are covered by a centrally-attached, umbrella-like indusium with fringed edges. They produce light yellow spores. In deep shade, fronds spread nearly horizontally but with increasing sun exposure grow more upright.[3]
The preferred habitat of this fern is the understory of moist coniferous woodlands at low elevations. It grows best in well-drained acidic soil of rich humus and small stones. It is very resilient and survives occasional droughts, but flourishes only with consistent moisture and it prefers cool weather.
In cultivation, it also responds well to regular, light fertilization. While this fern is a favored horticultural subject in western North America, it has proved difficult or impossible to cultivate satisfactorily in the eastern part of the continent.
In the United Kingdom Polystichum munitum has gained the Royal Horticultural Society's Award of Garden Merit.[4][5]
According to a molecular phylogeny of Polystichum ferns based on plastid DNA sequences, P. munitum is most closely related to other North American Polystichum species, including the western species Polystichum lemmonii, Polystichum scopulinum, and Polystichum dudleyi, and the eastern species Polystichum acrostichoides.[6]
The Coast Salish people of B.C. and Washington state use this plant as a pain reliever. When applied directly to the area where pain and inflammation occur, according to Della Rice Sylvester, an elder and medicine woman of the Cowichan tribe, the sword fern "takes the pain away!". This traditional use has spread among the hiking communities and youth scouting organizations of the region, where it is a common piece of hiker's lore that a rash from a stinging nettle can be counteracted by rubbing the spores on the underside of sword fern on the area.
In spring, when other food is unavailable, Quileute, Makah, Klallam, Squamish, Sechelt, Haida, and other Native American/First Nations peoples roasted, peeled, and ate the rhizomes.[7] The fronds were used to line fire pits and food drying racks and as filling for mattresses.[8] The plant is also cultivated for its ornamental foliage, which florists include in vases.
Polystichum munitum, the western swordfern, is an evergreen perennial fern native to western North America, where it is one of the most abundant ferns in forested areas. It occurs along the Pacific coast from southeastern Alaska to southern California, and also inland east to southeastern British Columbia, northern Idaho and western Montana, with disjunctive populations in northern British Columbia, Canada; the Black Hills in South Dakota, United States; and Guadalupe Island off of Baja California, Mexico. Western swordfern is known to have locally naturalized in parts of Great Britain and Ireland.
