BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Polystichum munitum | Western Sword Fern 



GENERAL BOTANICAL CHARACTERISTICS : 
Western sword fern is a relatively large, evergreen, long-lived fern
with long fronds arching from a short, scaly, erect rhizome [39,63,69].
The sword-shaped fronds are from 20 to 72 inches long (50-180 cm) and
divided pinnately [32].  Individual fronds live for several years and
remain attached to the rhizome after withering [32].  The largest
leaflets or pinnae are 1.2 to 16 inches long (3-15 cm).  Spores are
borne in clusters called sori that are found between the midline and the
edge of the middle and upper pinnae [39,69].

Amount of light received influences western sword fern form.  Following
disturbance that removes the overstory or when plants occasionally
establish on rocky outcrops at high elevations, the fronds are dwarfed
and more erect.  This sun form of western swordfern also has pinnae that
are crisped and crowded so that they overlap and appear imbricated.
When shaded again, these plants return to normal form [69].  

In southwestern British Columbia the rhizomes of western sword fern were
found to be vesicular-arbuscular mycorrhizal, although some plants have
been found with nonmycorrhizal rhizomes [8].


RAUNKIAER LIFE FORM : 
   Chamaephyte
   Geophyte


REGENERATION PROCESSES : 
Regeneration of western sword fern is mostly sexual; however, only a few
small, juvenile plants are present in most populations [63].  Ferns
begin to produce spores on a regular, yearly basis when they are between
1 and 5 years of age [28].  From early to midsummer mature ferns produce
millions of light, wind-borne spores.  Evergreen ferns such as western
sword fern may retain some spores over the winter which are released the
following spring.  The dry spores are very resistant to extreme physical
conditions and may remain viable for 2 to 4 years, although their
viability and ability to germinate declines with age [57].

The most important factor in spore germination is sufficient moisture.
Temperatures between 59 and 86 degrees Fahrenheit (15-30 deg C) and a
slightly acid to neutral pH are generally best for germination [50].
Western sword fern is one of the few fern species which is capable of
germination in the dark, although germination is best in the light [71].

When spores germinate, they produce tiny, bisexual gamete-bearing plants
(gametophytes) that do not look like the spore-bearing plants.  These
tiny plants have no vascular system and require very moist conditions in
order to survive and enable the sperm to swim to the egg.  The
spore-bearing plant, which develops in place from the fertilized egg, is
initially dependent on the gametophyte but quickly becomes independent.
In many ferns the gamete-bearing plants are self-fertile, but
self-fertilization in western sword fern gemetophytes probably occurs
less than 4 percent of the time.  Outcrossing results in high levels of
genetic variability within and between western sword fern populations
[63].

Vegetative reproduction of western sword fern is limited but can occur
through division of its perennial, woody rhizome [28].  The rhizomes are
erect and do not spread, although they branch with age [63].


SITE CHARACTERISTICS : 
Light and water relations:  Western sword fern is found growing in shade
or in small openings within moist coniferous forests, while the
morphologically similar imbricated sword fern is found in distinctly
drier habitats, including rock crevices and dry coniferous forests
[39,69].  Western sword fern can survive very little moisture stress,
and thus in places on Vancouver Island where summer moisture deficits
are common, it is found only where seepage aguments the soil moisture
[28].  It may indicate a high water table in northwestern Oregon [65].
Western sword fern is a minor species in Oregon riparian communities.
Its frequency is greatest in outer edges of riparian zones [11].

An ecological study of the coastal redwood (Sequoia sempervirens) region
grouped species along environmental gradients of moisture, nutrients,
light, and temperature.  Western sword fern's distribution placed it in
the moderately moist to moist class.  It had a low to moderate nutrient
requirement.  Its ecological optimum light requirement was less than 3
percent, but it grew in areas having up to 40 percent of full sunlight
on a logarithmic light intensity scale [70].

Soils:  In the Siskiyou Mountains of California, western sword fern is
an important mesic species found primarily on soils formed from quartz
diorite.  Although a few plants are found in submesic conditions on
soils formed from olivine grabbro, imbricated sword fern is more common
on grabbro, and the only sword fern found on serpentine parent materials
[72].  In British Columbia western sword fern grows on a variety of
parent material but prefers deep, loamy soils derived from fluvial
parent materials.  It also prefers nutrient-rich soils and can be an
indicator of such soils when it is abundant and vigorous [28].  Soils of
most sites in coastal Oregon where western sword fern is dominant are
deep and formed from sandstone and siltstone [6].

Elevation:  Western sword fern grows from sea level to mid-elevations in
the mountains throughout its range [39].  Its elevational limit in
Montana is 3,000 feet (914 m).  In California it is usually found below
2,500 feet (762 m) [54].  In coastal Oregon it is found below 1,700 feet
(518 m) [6].

Common associates:  Associated understory species include salal
(Gaultheria shallon), salmonberry (Rubus spectabilis), thimbleberry (R.
parviflorus), vine maple (Acer circinatum), Oregon-grape (Mahonia
nervosa), twinflower (Linnaea borealis), oxalis, false
lily-of-the-valley (Maianthemum dilatatum), western springbeauty (Montia
sibirica), threeleaf foamflower (Tiarella trifoliata), evergreen violet
(Viola sempervirens), pioneer violet (V. glabella), red huckleberry
(Vaccinium parvifolium), evergreen huckleberry (V. ovatum), and rusty
menziesia (Menziesia ferruginea) [22].


SUCCESSIONAL STATUS : 
Facultative Seral Species

The light wind-borne spores of ferns enable them to swiftly colonize new
sites [57]; however, western sword fern's ability to colonize appears
limited by its sensitivity to water stress [28].  On Vancouver Island it
is not present during the pioneer stage of floodplain succession.
Establishment occurs only under the shelter of a red alder canopy, and
its frequency is greatest in the climax community [12].  In the
Douglas-fir zone of the Oregon Coast Range, seral communities are
commonly dominated by red alder/western sword fern.  These communities
may extend beyond the fog belt [7].  On western Oregon red
alder/salmonberry sites, western sword fern is found throughout
successional communities but increases with time [38].

In the Coast Ranges of Oregon, western sword fern survives disturbances
and becomes an important part of the seral vegetation while in the
Cascade Range it is of minor importance in early succession [22].  In
southwestern British Columbia forests, western sword fern is absent
immediately after disturbance but enters the stand within a few years.
It gradually becomes more dominant, regaining postdisturbance cover by
the sapling and pole stages [46].  Western sword fern is a dominant
plant in initial communities after logging or burning of California
coastal redwood forests, and remains dominant throughout succession
[77].  In the Olympic Mountains western sword fern colonizes recent
clearcuts but only takes its place as a principal understory species in
Douglas-fir forests when the stand is 300 years old or older [21].  In
coastal southern Oregon western hemlock, Douglas-fir, and western
red-cedar forest with western swordfern-Oregon oxalis understories,
western sword fern is dominant throughout succession, but its cover is
lower in densely shaded, near-climax stands than at any other time [6].
Its greatest cover in such dense forests occurs in canopy gaps [6,65].


SEASONAL DEVELOPMENT : 
In Oregon western sword fern fronds partially unroll by late May.  By
late July the spores are near maturity [66].

Related categories for Species: Polystichum munitum | Western Sword Fern