BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Epilobium angustifolium | Fireweed 



GENERAL BOTANICAL CHARACTERISTICS : 
Fireweed is a robust native perennial forb.  It has fine roots and
rhizomes that extend down vertically to 17.7 inches (45 cm) from the
plant, with most growing between 0 and 5.9 inches (0-15 cm) deep
[103,154,161].  The single stems are from 3 to 9 feet (1-2.7 m) tall and
may be very leafy [72,104].  Leaves are 2.8 to 5.9 inches (7-15 cm) long
[72].  One plant may have 15 or more flowers [29].  Each flower produces
a capsule with 300 to 500 seeds [72,196].  Seeds have a tuft of long
hairs on one end [196].


RAUNKIAER LIFE FORM : 
   Geophyte
   Hemicryptophyte


REGENERATION PROCESSES : 
Fireweed regenerates sexually and asexually.  Airborne seeds allow
fireweed to establish rapidly [93].  Hungerford [103] noted that an
opening in a canopy was not enough to ensure fireweed establishment.
Fireweed requires bare mineral soil in addition to high light for
germination [137].  Moisture supply is more stable and more nutrients
are available on a mineral soil seedbed [137].  Once established, it
forms large colonies via rhizomes and produces large amounts of seed
[41].

Vegetative Reproduction:  Vegetative reproduction is more prevalent than
sexual reproduction [29].  Fireweed may not flower every year in the
northern limits of its range or at alpine eleveations in the southern
limits [43,185].

Fireweed readily sprouts from rhizomes following disturbance.  Fireweed
was a resudual survivor on Mount St. Helens, Washington, following the
1980 volcanic eruption [143,152].  Shoots sprouting from rhizomes are
capable of very rapid growth; they may bloom within 1 month [195].
Fragmentation of rhizomes stimulates shoot production [41].  A
4-year-old rhizome was excavated and found to be 20 feet (6.1 m) long;
it had 56 perennating buds.  Rhizome length depends on soil fertility
and amount of competing vegetation present [104].

Sexual Reproduction:  Fireweed flowers can self-cross or outcross [29].
They are principally pollinated by insects [29].  Fireweed is a prolific
seed producer [41].  One plant may produce about 80,000 seeds per year
[196].  In seed traps placed on a burn in Saskatchewan, fireweed
represented 63 percent of all germinated seeds [11].  One year after the
Mount St. Helens explosion, 81 percent of seed collected in seed traps
were fireweed seeds [55].  Fireweed was one of the most abundant
colonizers on Mount St. Helens [143,152,158].

Seeds are nondormant and germinate over a variety of temperatures.  One
hundred percent of newly collected fireweed seeds germinated within 10
days [29].  Fireweed does not create a long-lived seedbank [10,110,146].
Most seeds lose viability after 18 to 24 months [29,43,87].  Optimum
germinating conditions are warm, well-lighted, and humid [29].  Seed
collected from subalpine (9,285 feet [2,830 m]) meadows in the Sierra
Nevada, California, gave 55 to 68 percent germination under day/night
temperature regimes of 62/55 degrees Fahrenheit (17/13 deg C) and 81/73
degrees Fahrenheit (27/23 deg C), respectively.  The lowest percent
germination (12 percent) was at 53.6/46.4 degrees Fahrenheit (12/8 deg
C) [37].  Broderick [29] reported similar germination rates; however, he
saw 86 percent germination at 86 degrees Fahrenheit (30 deg C).

Fireweed seed hairs or plumes respond to humidity.  Increased humidity
causes a decreased plume diameter which results in reduced loft [55].
This increases the chance that seeds are deposited in places with
moisture adequate for germination.  Plumed seed has low rates (0.21 to
0.23 foot per second [0.065-0.069 m/s]) of fall in still air [196].
Using modified insect suction traps mounted on radio towers, Solbreck
and Andersson [196] found that 20 to 50 percent of the seeds sampled at
328 feet (100 m) in an air column above a burned forest in Sweden were
fireweed seeds.  Since the seeds were commonly aloft for 10 hours per
day, they suggested that the seeds traveled 62.2 to 186.5 miles (100-300
km) during that time.  Broderick [29] reported that the seed rain of
fireweed for all of northern Quebec was 3.7 seeds per square foot (40
seeds/sq m).


SITE CHARACTERISTICS : 
Fireweed tolerates a wide range of site and soil conditions, but it most
commonly occurs on disturbed ground.  It is abundant in coniferous
forests, mixed forests, aspen parklands, grasslands, sylvotundra (i.e.,
area between treeless tundra and circumpolar coniferous forest), and
muskegs [54,134,144,163,210].  Fireweed grows on disturbed areas such as
cut-over or burned forests and swamps, avalanche areas, recently
deglaciated areas, and riverbars [22,101,153,208].  Additional disturbed
sites are highway and railroad rights-of-way, waste places, and old
fields [94,188].

In North America, fireweed occurs in maritime to strongly continental
climates with short, warm summers and long, cold winters [28,229].
Annual precipitation averages between 13 inches (330 mm) on the
north-central edge of its range and 134.7 inches (3,420 mm) on the west
coastal edge [4,28].

Fireweed occurs on soils that vary from thin layers above permafrost in
the subarctic regions to deep loams in the western United States [136].
Soil development ranges from clays and clayey loams to sandy loams to
unweathered parent material [4,73].  Organic matter may be low in
fireweed soils or very high and peaty [227].  Low soil pH may affect
plant fertility.  Fireweed grown in soil with pH 3.5 produced 80 percent
fewer seeds than plants grown in soil with pH 5.0 [29].  Fireweed may
occur in neutral soils [48,208].  Northern soils in which fireweed
occurs may be frozen 4 to 5 months or longer [29].

Fireweed occurs on flat to rolling topography or moderate to steep
slopes [12].  It is found from sea level to high alpine elevations
[89,185].  Mueggler [162] found no significant (p>0.05) effect of aspect
on the frequency of fireweed in burned areas in Idaho.

Fireweed has numerous common associates.  Trees associated with fireweed
include Gambel oak (Quercus gambelii), bur oak (Q. macrocarpa),
American hazel (Corylus americana), Alaska-cedar (Chamaecyparis
nootkatensis), and swamp black gum (Nyssa biflora) [22,53,69,153].

Common shrubs found with fireweed are snowbrush (Ceanothus velutinus),
snowberry (Symphoricarpos oreophilus), thimbleberry (Rubus parviflorus),
salmonberry (Rubus spectabilis), prickly rose (Rosa acicularis), hoary
willow (Salix candida), black twinberry (Lonicera involucrata), and
common juniper (Juniperus communis) [123,130,134,136,178,229].

Other postdisturbance species associated with fireweed are bluejoint
reedgrass (Calamagrostis canadensis), pinegrass (C. rubescens), purple
reedgrass (C. purpurascens), and Wyoming wildrye (Leymus flavescens)
[65,97,136,190,227].  In moister grasslands, fireweed occurs with sedges
(Carex spp.) and sailorcaps shootingstar (Dodecatheon conjugens) [210].
Pteridophyte associates are western swordfern (Polystichum minutum),
brackenfern (Pteridium aquilinum), and woodland horsetail (Equisetum
sylvaticum) [21,229].  Important liverwort and moss associates are
Marchantia polymorpha and Ceratodon purpureus [226]. (Also see
Distribution and Association)


SUCCESSIONAL STATUS : 
Fireweed is an important colonizer following vegetation disturbances in
temperate climates worldwide [46,157].  Although the role of fireweed as
an early seral species does not change, the length of time fireweed
populations are present varies among ecosystems.  Fireweed enters a
disturbed community and rapidly becomes abundant.  It may acheive a peak
in dominance within 2 to 3 years [43].  It starts low in frequency and
density if it must seed in from off-site [118].  Halpern [86] found that
after disturbance in Douglas-fir (Pseudotsuga menziesii) forests in
Oregon, fireweed cover peaked in year 7 and then slowly declined.

Fireweed populations can maintain themselves through vegetative
reproduction if conditions are not conducive to flowering.  Depending
upon surrounding vegetation fireweed may create widely spaced colonies
with low stem densities [29].  In Alaska, ground that was covered 30
years by debris from oil exploration was cleared or burned [64].
Fireweed vegetatively colonized these areas at low frequencies and
cover.  In 20 study sites in Montana, Stickney [202] reported that
fireweed established with about 3 percent cover 1 year after
disturbance.  By the second year, it peaked at about 30 percent cover
and stayed around this amount for the next 8 years.

Fireweed is one of the first plants to enter a community during the
seedling/herb stage [3,50].  This may last 1 to 15 years in the Yukon
Territory [92].  Sometimes, it will persist into the pole stage [84].
Young forests differ in the range of microhabitats (i.e., variations in
light, nutrients, and moisture) available; fireweed will persist if a
stand is open [43].

Moore [157] stated that fireweed declined in successional communities
because soil conditions became unsuitable for growth as nutrients are
leached out.  However, other studies suggest that fireweed declines due
to the effects of competing vegetation [149,207].  Progressive changes
from open to closed canopy in a forest result in decreasing abundance of
fireweed [3,40,207].  Several studies report that fireweed is shade
intolerant [81,115,124,157,182,217].  However, it can exist in partial
shade with a corresponding reduction in productivity [200].  Shirley
[192] found that fireweed response to Norway pine (Pinus resinosa)
canopy cover was variable.  At 5 percent of total sunlight, fireweed
occurred with 62 percent frequency; at 10 percent of total sunlight,
fireweed occurred with 100 percent frequency [192].  Frequency of
fireweed plants declined to 50 percent at 45 percent of total sunlight
and then, increased to 100 percent frequency at 65 to 100 percent of
total sunlight.  Mueggler [162] found a significant (p<0.05) decrease in
fireweed frequency when tree canopy cover exceeded 41 percent.

Fireweed colonizes recent alluvial deposits [132].  It acts as a pioneer
species on glacial moraines, establishing with willows (Salix spp.) on
exposed gravel, sand, and silt bars [216,226].  In Glacier Bay, Alaska,
the pioneer stage with fireweed and willows lasts 1 to 5 years [213].

In succession on delta swamps in Michigan, the grass stage with
bluejoint reedgrass and fireweed follows the sedge-mat stage.  The grass
stage is succeeded by a shrub stage [44].

Fireweed is an indicator of a mid-seral stage of succession in the herb
layer of the grand fir/Rocky mountain maple (Abies grandis/Acer glabrum)
habitat type in central Idaho [200].  It is an indicator of early seral
stages in grand fir/blue huckleberry (Vaccinium globulare) habitat types
[198].


SEASONAL DEVELOPMENT : 
The time ranges given here for the phenological stages of fireweed
reflect its widespread distribution, varying from region to region and
from habitat to habitat.  Root growth can begin at 40 degrees Fahrenheit
(4.5 deg C), preceeding stem emergence [29].  Shoots emerge in spring
(late March to early June).  Leaves are full grown approximately 1 month
after emergence [43].  Maximum biomass occurs in summer (August) and may
be 0.12 to 0.19 pounds per square foot (0.6-0.9 kg/sq m) [43].  Flowers
bloom June through September [83,111,164,188,191,224].  Fruits mature
approximately 1 month later [187].  Seeds are released beginning in
August and continue to be shed after shoots have died from frost injury
[43,187].  Foliage will turn color with limited water availability in
the late summer and fall [62].  Seeds germinate late summer or fall, and
seedlings overwinter as a rosette [43].  The primary and secondary roots
of seedlings may develop buds which overwinter [195].  Shoot buds form
in the fall on lateral roots and overwinter just below the soil surface
[29].

Related categories for Species: Epilobium angustifolium | Fireweed