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Wildlife, Animals, and Plants
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Introductory
SPECIES: Populus tremuloides | Quaking Aspen
ABBREVIATION :
POPTRE
SYNONYMS :
Populus tremuloides var. aurea Tidestr. [91]
P. tremuloides var. magnifica Vict.
P. tremuloides var. pendula Jaeger & Bessner
P. tremuloides var. reniformis Tidestr. [150]
SCS PLANT CODE :
POTR10
COMMON NAMES :
quaking aspen
trembling aspen
aspen
TAXONOMY :
The scientific name of quaking aspen is Populus tremuloides Michx.
(Salicaceae) [60,64,75,78,82,79,165,166]. There are no currently
recognized subspecies or varieties [64,75,78,100,136,165,166]. Roland
and Smith [136] recognize a form with extremely broad leaves, P.
tremuloides forma reniformis Tidestr., that occurs in northeastern North
America.
Quaking aspen is in subsection Trepidae of the genus Populus. Some
authorities consider the Trepidae aspens a single taxonomic entity.
Under this treatment, quaking aspen, bigtooth aspen (P. grandidentata),
European aspen (P. tremula), and three aspens occurring in Asia are
classed together as a single, circumglobal superspecies [126].
Quaking aspen hybridizes naturally with bigtooth aspen and white poplar
(P. alba), a naturalized European species. Hybrid quaking
aspen-bigtooth aspen swarms occur in the Niobrara River valley of
Wyoming and Nebraska [64], and quaking aspen-bigtooth aspen hybrids are
common in some eastern locales [73]. Black cottonwood (P. trichocarpa)-
quaking aspen hybrids occur rarely in Alaska [82].
Quaking aspen has been crossed with several Populus species,
particularly the Eurasian species gray poplar (P. canescens), European
aspen, and white poplar, in tree breeding programs [88].
LIFE FORM :
Tree
FEDERAL LEGAL STATUS :
No special status
OTHER STATUS :
NO-ENTRY
COMPILED BY AND DATE :
D. Tirmenstein, May 1988
LAST REVISED BY AND DATE :
Janet L. Howard, September 1996
AUTHORSHIP AND CITATION :
Howard, Janet L. 1996; Tirmenstein, D. 1988. Populus tremuloides. In: Remainder of Citation
DISTRIBUTION AND OCCURRENCE
SPECIES: Populus tremuloides | Quaking Aspen
GENERAL DISTRIBUTION :
Quaking aspen is the most widely distributed tree in North America. It
occurs from Newfoundland west to Alaska and south to Virginia, Missouri,
Nebraska, and northern Mexico. A few scattered populations occur
further south in Mexico to Guanajuato [99]. Quaking aspen is
distributed fairly continuously in the East. Distribution is patchy in
the West, with trees confined to suitable sites. Density is greatest in
Minnesota, Wisconsin, Michigan, Colorado, and Alaska; each of those
states contains at least 2 million acres of commercial quaking aspen
forest. Maine, Utah, and central Canada also have large acreages of
quaking aspen [89,125].
ECOSYSTEMS :
FRES10 White-red-jack pine
FRES11 Spruce-fir
FRES15 Oak-hickory
FRES17 Elm-ash-cottonwood
FRES18 Maple-beech-birch
FRES19 Aspen-birch
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES22 Western white pine
FRES23 Fir-spruce
FRES24 Hemlock-Sitka spruce
FRES25 Larch
FRES26 Lodgepole pine
FRES28 Western hardwoods
FRES29 Sagebrush
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES36 Mountain grasslands
FRES37 Mountain meadows
FRES38 Plains grasslands
FRES39 Prairie
STATES :
AK AZ CA CO CT ID IL IN IA KY
MA ME MD MI MN MO MT NE NV NH
NJ NM NY ND OH OR PA RI SD TX
UT VT VA WA WV WI WY AB BC MB
NB NF NT NS ON PE PQ SK YT MEXICO
ADMINISTRATIVE UNITS :
ACAD ALPO APIS BAND BIBE BICA
BLCA BRCA CANY CACO CACA CEBR
COLO CRLA CRMO CURE CUVA DENA
DEPO DETO DINO EFMO ELMA FIIS
GATE GETT GLAC GLBA GRBA GRCA
GRPO GRTE GUMO HAFE INDU ISRO
JOFL KOVA LABE MANA MORR MORA
MEVE NAVA NACA NOCA OLYM PIRO
ROMO ROVA SAGA SAJU SARA SEKI
SHEN SLBE SUCR THRO VOYA WACA
WRST YELL YOSE ZION
BLM PHYSIOGRAPHIC REGIONS :
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands
KUCHLER PLANT ASSOCIATIONS :
K003 Silver fir-Douglas-fir forest
K005 Mixed conifer forest
K007 Red fir forest
K008 Lodgepole pine-subalpine forest
K011 Western ponderosa forest
K012 Douglas-fir forest
K013 Cedar-hemlock-pine forest
K014 Grand fir-Douglas-fir forest
K015 Western spruce-fir forest
K016 Eastern ponderosa forest
K017 Black Hills pine forest
K018 Pine-Douglas-fir forest
K019 Arizona pine forest
K020 Spruce-fir-Douglas-fir forest
K021 Southwestern spruce-fir forest
K022 Great Basin pine forest
K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K029 California mixed evergreen forest
K037 Mountain-mahogany-oak scrub
K038 Great Basin sagebrush
K055 Sagebrush steppe
K095 Great Lakes pine forest
K096 Northeastern spruce-fir forest
K098 Northern floodplain forest
K100 Oak-hickory forest
K101 Elm-ash forest
K106 Northern hardwoods
K107 Northern hardwoods-fir forest
K108 Northern hardwoods-spruce forest
SAF COVER TYPES :
1 Jack pine
5 Balsam fir
12 Black spruce
13 Black spruce-tamarack
15 Red pine
16 Aspen
18 Paper birch
19 Gray birch-red maple
20 White pine-northern red oak-red maple
21 Eastern white pine
25 Sugar maple-beech-yellow birch
26 Sugar maple-basswood
27 Sugar maple
28 Black cherry-maple
30 Red spruce-yellow birch
31 Red spruce-sugar maple-beech
32 Red spruce
33 Red spruce-balsam fir
35 Paper birch-red spruce-balsam fir
37 Northern white-cedar
38 Tamarack
39 Black ash-American elm-red maple
42 Bur oak
51 White pine-chestnut oak
55 Northern red oak
60 Beech-sugar maple
63 Cottonwood
107 White spruce
108 Red maple
201 White spruce
202 White spruce-paper birch
203 Balsam poplar
204 Black spruce
205 Mountain hemlock
206 Engelmann spruce-subalpine fir
207 Red fir
208 Whitebark pine
209 Bristlecone pine
210 Interior Douglas-fir
211 White fir
212 Western larch
213 Grand fir
215 Western white pine
216 Blue spruce
217 Aspen
218 Lodgepole pine
219 Limber pine
220 Rocky Mountain juniper
238 Western juniper
239 Pinyon-juniper
252 Paper birch
256 California mixed subalpine
SRM (RANGELAND) COVER TYPES :
105 Antelope bitterbrush-Idaho fescue
107 Western juniper/big sagebrush/bluebunch wheatgrass
318 Bitterbrush-Idaho fescue
401 Basin big sagebrush
402 Mountain big sagebrush
403 Wyoming big sagebrush
411 Aspen woodland
412 Juniper-pinyon woodland
413 Gambel oak
420 Snowbush
421 Chokecherry-serviceberry-rose
422 Riparian
509 Transition between oak-juniper woodland and mahogany-oak association
920 White spruce-paper birch
HABITAT TYPES AND PLANT COMMUNITIES :
Quaking aspen is a major cover type in North America. In Minnesota,
Wisconsin, and Utah, quaking aspen occupies more land than any other
forest type. Quaking aspen also occurs in a large number of other
forest cover types over its extensive range. It is common in spruce-fir
(Picea-Abies spp.) types of the Great Lakes States and central Canada
and in mixed northern hardwoods. Mixed jack pine (Pinus banksiana) and
quaking aspen occur on the Precambrain shield in Canada and Minnesota.
In the Rocky Mountains, quaking aspen groves are scattered throughout
Engelmann spruce-subalpine fir (Picea engelmannii-A. lasiocarpa)
forests. Quaking aspen is common in mixed conifer forests of New
Mexico, Arizona, and California. At its lower altitudinal limit in the
western United States, quaking aspen is associated with scrub oaks
(Quercus spp.) or sagebrush (Artemisia spp.). Prostrate quaking aspen
occur above timberline [125]. Throughout its range, quaking aspen
occurs in mid- to upper riparian zones [56,123].
Quaking aspen is listed as a dominant species in over 100 habitat, plant
community, and vegetation typings. A comprehensive list of these
publications can be obtained by using the Citation Retrieval System
(CRS). In CRS, a combination search using the keywords POPTRE and HTS
(Populus tremuloides and habitat types), and a second search using the
keywords POPTRE and COMM TYPES (P. tremuloides and community types),
will produce a list of habitat, plant community, and vegetation typings
describing quaking aspen as a dominant species. The search can be
narrowed by including the keyword for the state or administrative unit
of interest (e.g., search: POPTRE and HTS and CO).
Associated shrub species: East - Shrub species commonly associated with
quaking aspen in the East include beaked hazel (Corylus cornuta),
American hazel (C. americana), mountain maple (Acer spicatum), speckled
alder (Alnus rugosa), American green alder (A. viridis spp. crispa),
dwarf bush-honeysuckle (Diervilla lonicera), raspberries and
blackberries (Rubus spp.), willows (Salix spp.), and gooseberries (Ribes
spp.).
Great Plains - Additional species occurring with quaking aspen in the
prairie provinces inclued snowberry (Symphoriocarpos spp.), highbush
cranberry (Viburnum edule), limber honeysuckle (Lonicera dioica),
red-osier dogwood (Cornus sericea), western serviceberry (Amelanchier
alnifolia), chokecherry (Prunus virginiana), Bebb willow (Salix
bebbiana), and roses (Rosa spp.).
Alaska - Bebb willow and roses are also associated with quaking aspen in
Alaska. Other common shrub associates are Scouler willow (S.
scouleriana), bearberry (Arctstaphylos uva-ursi), mountain cranberry
(Vaccinium vitis-idaea), and highbush cranberry.
Rocky Mountains - Mountain snowberry (Symphoriocarpos oreophilus),
western serviceberry, chokecherry, common juniper (Juniperus communis),
Oregon-grape (Berberis repens), Wood's rose (R. woodsii), myrtle
pachistima (Pachistima myrsinites), redberry elder (Sambucus pubens),
and a number of Ribes species are associated with quaking aspen in the
Rocky Mountains [123].
Pacific Northwest - In valleys west of the Cascades in Oregon and
Washington, quaking aspen alternates dominance with Douglas hawthorn
(Crataegus douglasii). Quaking aspen grows through the Douglas hawthorn
overstory, resulting in reduced vigor of Douglas hawthorn. Quaking
aspen eventually dies back, releasing Douglas hawthorn in the understory
[56].
Associated herbaceous species: East - Herbs commonly found in the
understory of quaking aspen in the East include largeleaf aster (Aster
macrophyllus), wild sarsaparilla (Aralia nudicaulis), Canada beadruby
(Maianthemum canadense), bunchberry (Cornus canadensis), yellow beadlily
(Clintonia borealis), roughleaf ricegrass (Oryzopsis asperifolia),
sweet-scented bedstraw (Galium triflorum), sweetfern (Comptonia
perigrina), lady fern (Athyrium filix-femina), bracken fern (Pteridium
aquilinum), sedges (Carex spp.), and goldenrods (Solidago spp.).
West - The herbaceous component of quaking aspen communities in the West
is too diverse to list. Forbs dominate most sites [123].
VALUE AND USE
SPECIES: Populus tremuloides | Quaking Aspen
WOOD PRODUCTS VALUE :
Quaking aspen is one of the most important timber trees in the East.
Its wood is used primarily for particleboard, especially waferboard and
oriented strandboard, and for pulp. In the Great Lakes States, quaking
aspen is the preferred species for making oriented strandboard. Quaking
aspen fibers are well suited for making fine paper. Some quaking aspen
is used for lumber. Quaking aspen lumber is used for making boxes,
crates, pallets, and furniture. A small but growing volume is made into
studs. Quaking aspen wood is little used in the West, except in
Colorado, where it is used for pulp and particleboard [125]. Specialty
products from quaking aspen wood include excelsior, matchsticks, and
tongue depressors. Quaking aspen pellets are used for fuel [125,170].
The wood of quaking aspen is light, soft, and straight grained. It has
good dimensional stability and it turns, sands, and holds glue and paint
well. It has relatively low strength, however, and is moderately low in
shock resistance. Both sapwood and heartwood have low decay resistance
and are difficult for preservatives to penetrate [125,170]. Quaking
aspen wood warps with conventional processing, but saw-dry-rip
processing controls warping [101].
IMPORTANCE TO LIVESTOCK AND WILDLIFE :
Quaking aspen forests provide important breeding, foraging, and resting
habitat for a variety of birds and mammals. Wildlife and livestock
utilization of quaking aspen communities varies with species composition
of the understory and relative age of the quaking aspen stand. Young
stands generally provide the most browse. Quaking aspen crowns can grow
out of reach of large ungulates in 6 to 8 years [116]. Although many
animals browse quaking aspen year-round, it is especially valuable
during fall and winter, when protein levels are high relative to other
browse species [159].
Large wild ungulates: Elk browse quaking aspen year-round in much of
the West, feeding on bark, branch apices, and sprouts [38,42,102]. In
some areas, elk use it mainly in winter [116]. In northwestern Wyoming,
elk begin browsing quaking aspen as soon as they move onto winter ranges
in November and continue to use it through March [6].
Quaking aspen is important forage for mule and white-tailed deer. Deer
consume the leaves, buds, twigs, bark, and sprouts [42,102,158]. New
growth on burns or clearcuts is especially palatable to deer [42,43].
Deer in many areas use quaking aspen year-round [23], although in some
western states, deer winter below the aspen zone [42,43]. Quaking aspen
communities are described as the major "deer-producing forest type" in
the north-central United States [31]. In the Great Lakes States,
quaking aspen is primary browse for white-tailed deer and moose [23].
Stands less than 30 years of age provide optimum forage for deer in
Minnesota [31]. In some locations, sprouts provide key summer forage
for deer after herbaceous species have cured [42,43]. Quaking aspen is
one of the most important items in the summer diet of mule deer on the
Kaibab National Forest of Arizona [159,161], and comprises up to 27
percent of the summer diet of mule deer in parts of central Utah [113].
However, it is relatively unimportant deer browse in parts of South
Dakota [159]. Mule deer in Utah have been observed consuming large
amounts of quaking aspen leaves after autumn leaf fall [42,161].
Quaking aspen is valuable moose browse for much of the year [23]. Moose
utilize it on summer [42] and winter ranges [23,42,135]. Quaking aspen,
paper birch (Betula papyrifera), and willows (Salix spp.) make up more
than 95 percent of the winter hardwood browse utilized by moose on
Alaska's Kenai Peninsula [149]. Relatively high levels of moose use
have been reported from early summer through late fall in Minnesota [84]
and Idaho [135]. Young stands generally provide the best quality moose
browse [42]. However, researchers in Idaho found that in winter, moose
browsed mature stands of quaking aspen more heavily than nearby
clearcuts dominated by quaking aspen sprouts [135].
Bison once favored quaking aspen-grassland transition zones in Manitoba
and Saskatchewan [32,102]. However, little is known about the historic
importance of quaking aspen browse to bison. Meagher [105] found that
woody plants made up only 1 percent of the diet of bison in Yellowstone
National Park, and she did not list quaking aspen as one of the woody
species bison used.
Bears: Black and grizzly bears feed on forbs and berry-producing shrubs
in quaking aspen understories. Quaking aspen forests in Alberta provide
excellent denning and foraging sites for black bear [42].
Lagomorphs: Rabbits and hares feed on quaking aspen in summer and
winter [42,43]. In winter, shoeshoe hare and cottontail rabbits eat
quaking aspen buds, twigs, and bark [42,43]. Quaking aspen is one of
the most important and nutritious summer browse species for rabbits in
Alberta [42], and is a preferred winter food of snowshoe hare in
Manitoba [20]. Pikas also feed on quaking aspen buds, twigs, and bark
[158]. Lagomorphs may girdle suckers or even mature trees [23,102]. In
some parts of Canada, fairly high quaking aspen mortality has been
attributed to rabbits and hares [20,102].
Rodents and shrews: Small rodents such as squirrels, pocket gophers,
mice, and voles feed on quaking aspen during at least part of the year
[43,88,158]. Mice and voles frequently consume quaking aspen bark below
snow level, and can girdle suckers and small trees [23,43,88,152]. The
southern red-backed vole, deer mouse, and white-footed mouse are
dominant small mammals in quaking aspen communities of northern
Minnesota and upper Michigan. Small mammal populations in quaking aspen
generally fluctuate widely with stand age and annual variation in animal
population size. Highest densities typically occur in mature quaking
aspen stands. Field mice (Peromyscus spp.), for example, are most
abundant in mature quaking aspen communities [129]. The red-backed
vole, however, is most abundant in sapling stands, somewhat less
abundant in mature stands, and least common in clearcuts.
Quaking aspen provides food for porcupine in winter and spring
[23,42,43]. In winter, porcupine eat the smooth outer bark of the upper
trunk and branches. Porcupine girdling of quaking aspen has killed
large tracts of merchantable trees in Minnesota. In spring, porcupine
eat quaking aspen buds and twigs [43].
Beaver comsume the leaves, bark, twigs, and all diameters of quaking
aspen branches [43]. They use quaking aspen stems for constructing dams
and lodges [42,102]. At least temporarily, beaver can eliminate quaking
aspen from as far as 400 feet (122 m) from waterways [6,23]. An
individual beaver consumes 2 to 4 pounds (1-2 kg) of quaking aspen bark
daily, and it is estimated that as many as 200 quaking aspen stems are
required to support one beaver for a 1-year period [42,43].
Birds: Quaking aspen communities provide important feeding and nesting
sites for a diverse array of birds [39]. Bird species using quaking
aspen habitat include sandhill crane, western wood pewee, six species of
ducks, blue, ruffed, and sharp-tailed grouse, band-tailed pigeon,
mourning dove, wild turkey, red-breasted nuthatch, and pine siskin.
Quaking aspen is host to a variety of insects that are food for
woodpeckers and sapsuckers [42]. Generally, moist to mesic quaking
aspen sites have greater avian species diversity than quaking aspen
stands on dry sites [40,42].
Many bird species utilize quaking aspen communities of only a particular
seral stage. Research at a northern Utah site suggests that blue
grouse, yellow-rumped warbler, warbling vireo, dark-eyed junco, house
wren, and hermit thrush prefer mature quaking aspen stands. The
MacGillivray's warbler, chipping and song sparrows, and lazuli bunting
occur in younger stands [39,42]. Bluebirds, tree swallow, pine siskin,
yellow-bellied sapsucker, and black-headed grosbeak favor quaking aspen
community edges [39].
Ruffed grouse: Through most of its range, ruffed grouse depends on
quaking aspen for foraging, courting, breeding, and nesting sites
[23,42,70]. It uses quaking aspen communities of all ages. Favorable
ruffed grouse habitat includes quaking aspen stands of at least three
different size classes [23,70]. Young (2- to 10-year-old) stands
provide important brood habitat, and 10- to 25-year-old stands are
favored overwintering and breeding areas [122]. Quaking aspen leaves
and buds are readily available in abundant quantities in stands greater
than 25 years of age, and such older stands are used for foraging
[70,122].
Ruffed grouse chicks find protection in dense, young aspen suckers as
early as 1 year after fire or other disturbance [70]. Pole-size stands
appear to offer the best breeding habitat and may support one breeding
bird per 3 to 4 acres (1.2-1.6 ha). Breeding generally does not occur
in stands exceeding 25 years of age or with a density less than
approximately 2,000 stems per acre [23].
Quaking aspen buds, catkins, and leaves provide an abundant and
nutritious, year-long food source for ruffed grouse [23,70]. Vegetative
and flower buds are the primary winter and spring foods of the ruffed
grouse. Ruffed grouse eat 6 times more quaking aspen buds than buds
from all other species combined [70]. It is estimated that ruffed
grouse can consume more than 45 quaking aspen buds per minute and can
satisfy their daily winter food needs in as little as 15 to 20 minutes
[23]. Ruffed grouse generally begin feeding on staminate flower buds
from several weeks prior to the period of snow accumlation, and continue
well into early spring [23,70]. Male ruffed grouse feed on staminate
catkins until at least early May [70]. Nesting hens consume large
quantities of new quaking aspen leaves early in the spring [23,70].
Ruffed grouse consume quaking aspen leaves throughout the summer [23],
and the leaves are considered to be the second most important food
source during the fall. Ruffed grouse appear to prefer certain clones.
Buds from some clones may be up to 30 percent richer in protein than
buds from neighboring clones [70].
Livestock: Most classes of domestic livestock use quaking aspen.
Domestic sheep and cattle browse the leaves and twigs [158,161].
Domestic sheep browse quaking aspen more heavily than cattle [158,161].
It is estimated that domestic sheep consume 4 times more quaking aspen
sprouts than cattle. Heavy livestock browsing can adversely impact
quaking aspen growth and regeneration [42,43,161].
PALATABILITY :
Quaking aspen is palatable to all browsing livestock and wildlife
species [38,23,42,84,161,169]. The buds, flowers, and seeds are
palatable to many bird species including numerous songbirds and ruffed
and sharp-tailed grouse [42,168].
Palatability of quaking aspen for livestock and wildlife species has
been rated as follows [48]:
CO MT ND OR UT WY
Cattle Fair Fair Fair ---- Fair Fair
Domestic sheep Fair Good Good ---- Fair Good
Horses Fair Fair Fair ---- Fair Fair
Pronghorn ---- ---- Poor ---- Fair Fair
Elk Good Fair ---- ---- Good Good
Mule deer Good Fair Fair ---- Good Good
White-tailed deer Good Fair Fair ---- ---- Good
Small mammals ---- Fair ---- ---- Fair Good
Small nongame birds ---- Fair Fair ---- Fair Fair
Upland game birds ---- Good Good ---- Fair Good
Waterfowl ---- ---- ---- ---- Poor Poor
NUTRITIONAL VALUE :
Overall energy and protein values of quaking aspen are rated "fair"
[48]. Nutritional content of quaking aspen browse varies seasonally, by
plant part, and by clone [11,40,159]. Protein content drops as the
growing season progresses [42,179]. On a Utah site, average leaf
protein dropped from 17 percent in early June to 3 percent at
abscission. Clonal variation in leaf protein ranged from 13.4 to 20.9
percent in June and from 10.1 to 14.6 percent in September. Average
twig protein dropped from 17 percent in spring to 6 to 7 percent in
winter. Twig nitrogen, phosphorus, and potassium levels dropped from
spring to winter, but twig calcium, magnesium, sodium, and fat levels
increased. Phosphorus values in September averaged only 58 percent of
those in June [159].
Mean composition of quaking aspen terminal shoots, collected in March
and April in Soldotna, Alaska, was as follows [149]:
dry matter (%) 43.6
gross energy (kcal/g) 5.1
crude protein (%) 7.9
neutral-detergent fiber (%) 54.9
acid-detergent fiber (%) 40.1
lignin (%) 10.5
ash (%) 1.9
in-vitro digestibilty for moose (%) 42.0
COVER VALUE :
Wild and domestic ungulates use quaking aspen for summer shade, and
quaking aspen provides some thermal cover for ungulates in winter
[42,35,152]. Seral quaking aspen communities provide excellent hiding
cover for moose, elk, and deer [42,161]. Deer use quaking aspen stands
for fawning grounds in the West [94]. Ungulates generally do not use
quaking aspen much in winter. Perala [122] reported that in the Great
Lake States, pure quaking aspen stands provided white-tailed deer with
relatively poor insulation and protection from winter winds compared to
adjacent stands of conifers.
Quaking aspen provides good hiding and thermal cover for many small
mammals [152]. Snowshoe hare use it for hiding and resting cover in
summer [42,43]. Beaver use quaking aspen branches for dams and lodges.
A variety of bird species use quaking aspen for hiding, nesting, and
roosting cover [42]. Sapling and pole-size stands provide especially
good winter cover for birds [23]. Snow tends to accumulate earlier and
deeper in quaking aspen than in adjacent conifer stands, and ruffed
grouse use the deep snow for burrowing cover in winter [122]. Dense
stands of fairly small diameter stems (<6 inches [15cm]) provide the
best protection from predators. Overall cover value for ruffed grouse
is enhanced in stands containing several size classes [70].
Over 4 years, 22 to 65 pairs of breeding birds were found in 10 acres (4
ha) of quaking aspen in nothern Utah. Species nesting in quaking aspen
included the broad-tailed hummingbird, northern flicker, house wren,
American robin, warbling vireo, yellow-rumped warbler, junco, western
wood pewee, and lazuli bunting [39]. The following other species also
nest in mature quaking aspen communites [42]:
canopy nesters - pewees, vireos, western tanager, Cassin's finch,
least flycatcher
ground nesters - hermit thrush, Townsend`s solitaire, dark-eyed junco,
white-crowned and Lincoln`s sparrows, veery, ovenbird, nighthawk,
Connecticut and mourning warblers
shrub nesters - flycatchers (Empidonax spp.), rose-breasted and
black-headed grosbeaks, chipping, clay-colored, and song sparrows,
yellow and MacGillivray`s warblers, rufous-sided and
green-sided towhees, black-billed cuckoo
cavity nesters - chickadees, nuthatches, woodpeckers, owls,
sapsuckers, hairy and downy woodpeckers
General cover value of quaking aspen has been rated as follows [48]:
CO MT ND OR UT WY
Pronghorn ---- ---- Poor ---- Poor Poor
Elk Fair Good ---- ---- Good Good
Mule deer Fair Good Poor ---- Good Good
White-tailed deer Fair Good Fair ---- ---- Good
Small mammals ---- Good ---- ---- Good Good
Small nongame birds Good Good Good ---- Good Good
Upland game birds Poor Good Good ---- Good Good
Waterfowl ---- ---- ---- ---- Poor Poor
VALUE FOR REHABILITATION OF DISTURBED SITES :
Aspens (Trepidae) are unique in their ability to stabilize soil and
watersheds. Fire-killed stands are promptly revegetated by root sprouts
(suckers). The trees produce abundant litter that contains more
nitrogen, phosphorus, potash, and calcium than leaf litter of most other
hardwoods. The litter decays rapidly, forming a nutrient-rich humus
that may amount to 25 tons per acre (oven-dry basis). The humus reduces
runoff and aids in percolation and recharge of ground water. Litter and
humus layers reduce evaporation from the soil surface. Compared to
conifers, more snow accumulates under quaking aspen and snowmelt begins
earlier in the spring. Soil under quaking aspen thaws faster and
infiltrates snow more rapidly than soil under conifers [23].
Wide adapability of quaking aspen makes it well-suited for restoration
and rehabilitation projects on a wide range of sites. Seedlings
transplanted onto disturbed sites have shown good establishment [33].
Seedlings have some advantages over vegetative cuttings. In large-scale
greenhouse production, quaking aspen seedlings are more economical to
establish and grow [57]. Seedlings grow a taproot and secondary roots
quickly, while quaking aspen cuttings can be slow to establish an
adequate root system [145]. Also, genetic diversity is greater among
seedlings than cuttings [146]. Seed stored at 4 degrees Fahrenheit (-20
deg C) has retained viability for at least 2 years. Fung and Hamel [57]
and Schier and others [145] provide procedures for collecting and
processing quaking aspen seed.
The major advantage of using quaking aspen cuttings is that clones with
desirable traits can be selected as parent stock. Quaking aspen
vegetative cuttings are difficult to root, however [123,146]. Stem
cuttings are especially difficult to root unless taken from young
sprouts. Root cuttings taken from young sprouts are generally most
successful. Schier and others [146] provide information on growing
quaking aspen cuttings in the greenhouse.
Case examples - Riparian: In riparian and lodgepole pine (Pinus
contorta) zones of Lost Canyon near Fresno, California, restoration was
needed after a hydroelectric plant pipe broke, scouring part of the
canyon. Quaking aspen seedlings showed 99.2 percent survival (or 357
live seedlings) and had a mean height of 10.6 inches (26.6 cm) 1 year
after transplant [33].
Strip-mined sites: Some old strip-mined sites in Pennsylvania, Ontario,
and elsewhere have not revegetated due to extreme acidity of the soil.
Quaking aspen is one of the first native tree species to volunteer on
these soils after application of lime [81,168].
Mine spoils: Quaking aspen transplants were successfully established on
phosphate mine spoils in southeastern Idaho that received only 18 inches
(450 mm) of annual precipitation [145].
OTHER USES AND VALUES :
Mountain slopes covered by quaking aspen provide high yields of
good-quality water. Quaking aspen intercepts less snow than conifers,
so snowpack is often greater under quaking aspen [44].
Well-stocked quaking aspen stands provide excellent watershed
proctection. The trees, the shrub and herbaceous understories, and the
litter of quaking aspen stands provide nearly 100 percent soil cover.
Soil cover and the intermixture of herbaceous and woody roots protect
soil except during very intense rains [44].
Quaking aspen is valued for its aesthetic qualities at all times of the
year. The yellow, orange, and red foliage of autumn particularly
enhances recreational value of quaking aspen sites [85].
Quaking aspen is widely used in ornamental landscaping [85].
MANAGEMENT CONSIDERATIONS :
It is somewhat unclear why some quaking aspen stands break up and die
while others remain stable. The age at which quaking aspen clones begin
to die probably has a genetic component. Site quality can also be a
major factor [143]. Is it well documented in the Great Lakes States
that environmental variables affect quaking aspen longevity [63,93].
Stands in this region may deteriorate* rapidly; more than half the trees
in a well-stocked stand may die in 6 years [63]. In Utah, however,
clone deterioration was found to occur over a number of generations of
sprouts [141]. Schier and Campbell [143] found that on the Wasatch
National Forest near Logan, Utah, concentrations of phosphorus and
percent silt were significantly lower on soils with deteriorating clones
than on soils with healthy clones. Ten deteriorating clones and ten
healthy clones were studied.
*Deteriorating stands are defined as those stands with a low density of
stems that are younger and smaller in size, and with poorer form and
higher crown:stem ratios, than healthy stands [143].
Cryer and Murray [36] speculated that both soil type and disturbance are
important in quaking aspen stability. As a quaking aspen stand matures,
a humus-rich (mollic) soil layer develops. Quaking aspen thrive for a
time, but without disturbance gradually begin to age and deteriorate.
With deterioration, the soil loses organic matter and thickness. With
loss of humus and litter, rapid percolation leaches the soil, which
becomes thinner, more acidic, and lower in nutrients. Acidic,
low-nutrient soils support conifers more readily than quaking aspen.
Disturbances such as burning or clearcutting tend to maintain quaking
aspen. If soil is already thin and acidic, however, clearcutting will
probably convert the site to conifers. Quaking aspen on such sites has
been observed to sprout, grow to about 3 feet (0.9 m) in height, and
begin to die. A deteriorating stand that is burned may be more likely
to revert to quaking aspen because burning increases soil pH and adds
organic carbon and nutrients to the soil. However, fire will probably
not rejuvenate the stand if quaking aspen biomass is so low that burning
does not appreciably raise soil pH and nutrient levels. Sucker vigor
will probably be low.
Range: There is increasing concern that in the West, poor quaking aspen
regeneration is due, at least in part, to wildlife overbrowsing young
sprouts [67]. Where browsing pressure is heavy, ungulates may remove
quaking aspen regeneration before it grows above browseline. To provide
for quaking aspen regeneration in such areas, enough quaking aspen must
be removed to create an unbrowsed surplus of new growth [122]. A few
areas of the West have such large elk populations that even after
large-scale wildfires, quaking aspen sprouts attained little height
growth because of intense browsing. In such areas, quaking aspen
sprouts probably require protection from browsing [90].
Promoting quaking aspen: Prescribed burning is one method of promoting
quaking aspen (see FIRE MANAGEMENT). When prescribed burning is not
desired or feasible, clearcutting or bulldozing is recommended [77,177].
Clearcutting often results in a sucker stand of 50,000 to 100,000 stems
per hectare [17,35,49]. A basal area of less than 4 trees/sq m/ha is
recommended to promote sprouting [87,122]. Partial cuttings seriously
inhibit sprouting because apical dominance is retained in standing
stems, and shade from standing stems reduces vigor of the few suckers
that do appear [49].
Clearcutting in southeastern boreal forest: Lavertu and others [98]
found that in balsam fir-northern white-cedar (Abies balsamea-Thjua
occidentalis) forest in Quebec, quaking aspen showed strong sprouting
response regardless of forest seral stage, number of quaking aspen
present before cutting, quaking aspen stem age, or quaking aspen root
density. After clearcutting on sites that had burned 46, 74, 143, 167,
and 230 years earlier, quaking aspen sprouted vigorously even on the
site that had not burned for 230 years, had only a single, living
quaking aspen stem, and the lowest quaking aspen root density of all
five site types. Initial sprouting densities were greater in younger
stands, but due to greater mortality of sprouts in younger stands,
differences in sprouting density between different-aged stands were not
significant 3 years after clearcutting.
Bulldozing: Carefully done, whole-tree bulldozing can stimulate quaking
aspen suckering [177,178]. Operations that cause deep cutting or
compaction of soil will reduce sprouting [177]. Shepperd [178] obtained
good quaking aspen regeneration by pushing over whole trees using a
rubber-tire skidder with the blade positioned above ground level. This
technique severed large roots to a distance of 3.3 to 5 feet (1-1.5 m)
from the stem. Five years after treatment, quaking aspen suckers
averaged 37,888 per hectare when slash was removed and 10,131 per
hectare with slash intact. In contrast, sites that were clearcut
averaged 17,544 stems per hectare (no slash) and 7,038 stems per hectare
(slash) [178].
Quaking aspen control: On some sites, it may be desirable to convert
quaking aspen to another vegetation type. Stand conversion may be
relatively easy on dry or poorly drained sites, or on sites were quaking
aspen is exposed to snow damage. Quaking aspen production is usually
low on such sites to begin with, and such stands are prone to breakup.
On other sites, it may not be possible to eliminate quaking aspen, but
quaking aspen can probably be reduced [49]. Very small clearcuts reduce
quaking aspen abundance because sprouting response is weak after such
treatment [114]. Girdling also reduces adundance; sprouting occurs
after girdling, but shade provided by standing dead stems increases
sprout mortality. Also, it is thought that girdling promotes decay of
the root system [147]. Use of glyphosate after cutting has been shown
to control quaking aspen regeneration for some time [122,123].
In Quebec, quaking aspen in a quaking aspen-paper birch stand
originating after a 1944 fire was partially controlled by removing
overtopping quaking aspen when the stand was 7 and 14 years of age.
Stocking varied as follows at postfire year 34 [96].
_______________________________________________________________________________
Treatment | Stocking
______________________________|________________________________________________
control (no treatment) | 5% paper birch; 90% aspen; 5% mixed hardwoods
Aug. 1951 cut & Nov. 1958 cut | 90% paper birch; 10% aspen
Nov. 1951 cut & Nov. 1958 cut | 44% paper birch; 41% aspen; 15% mixed hardwoods
Nov. 1951 cut & May 1959 |
herbicide (injection in | 32% paper birch; 63% aspen; 5% mixed hardwoods
____aspen only)_______________|________________________________________________
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Populus tremuloides | Quaking Aspen
GENERAL BOTANICAL CHARACTERISTICS :
Quaking aspen is a native deciduous tree. It is small- to medium-sized,
typically less than 48 feet (15 m) in height and 16 inches (40 cm) dbh
[75]. It has spreading branches and a pyramidal or rounded crown
[60,75,88,166]. The bark is thin. Leaves are orb- to ovately shaped,
with flattened petioles [90]. The fruit is a tufted capsule bearing six
to eight seeds. A single female catkin usually bears 70 to 100 capsules
[88,166]. The root system is relatively shallow, with widespreading
lateral roots and vertical sinker roots descending from the laterals.
Laterals may extend over 100 feet (30 m) into open areas [88]. Gifford
[59] found that vertical roots of quaking aspen in Utah extended more
than 9 feet (2.7 m) down, branching into fine, dense roots at their
extremities [88].
Quaking aspen forms clones connected by a common parent root system. It
is typically dieocious, with a given clone being either male or female.
Some clones produce both stamens and pistils, however [88]. Quaking
aspen stands may consist of a single clone or aggregates of clones
[166]. Clones can be distinguished by differences in phenology, leaf
size and shape, braching habit, bark character, and by electrophoresis
[123]. In the West, quaking aspen stands are often even-aged,
originating after a single top-killing event. Some stands, resulting
from sprouting of a gradually deteriorating stand, may be only broadly
even-aged [88]. Clones east of the Rocky Mountains tend to encompass a
few acres at most [125], and aboveground stems are short lived. Maximum
age of stems in the Great Lakes States is 50 to 60 years. Clones in the
West tend to occupy more area, and aboveground stems may live up to 150
years [86]. A male clone in the Wasatch Mountains of Utah occupies 17.2
acres (43 ha) and has more than 47,000 stems. To date, it is the
world's most massive known organism. Clone age can be great; the large
Utah clone is estimated to be 1 million years old [107].
Seedling morphology: Quaking aspen seedlings can easily be
misidentified as cottonwood (Populus spp.) or willow (Salix spp.)
seedlings because quaking aspen seedlings bear only a slight resemblance
to the adult form. Leaves of quaking aspen seedlings are nearly
lanceolate. During the first growing season, vertical flattening of the
leaf petioles is not obvious, and there is no lateral branching. By the
second growing season, leaves are characterisitically orbicular to
ovate, and there is vertical branching. Renkin and others [133] have
published photographs of excavated quaking aspen seedlings.
Quaking aspen seedlings can be differentiated from root sprouts by leaf
morphology, lack of woody tissue, lack of vertical shoots, and presence
of a taproot [90,133]. There are a few visual clues that can
distinguish seedlings from sprouts without excavation. Seedlings have
paired cotyledons or cotyledon scars a few millimeters above the soil
surface. The first pair of true leaves is nearly opposite, at right
angles to, and directly above the cotyledons. Leaf pattern of sprouts
is strongly alternate [133].
Physiology: Quaking aspen is not shade tolerant [123,130]; neither does
it tolerate long-term flooding nor waterlogged soils [123]. Even if
quaking aspen survives flooding in the short term, stems subjected to
prolonged flooding usually develop a fungus infection that greatly
reduces stem life (and renders the wood commerically useless) [37,118,126].
Sprouting is hormonally controlled in quaking aspen. Sprouting is
suppressed by auxin, which is transported from the stem to the roots.
Auxin therefore maintains apical dominace. When stems are killed and
apical dominance is removed, cytokinins in the roots initiate root
sprouting. Clones with a strong tendency to sprout probably have high
cytokinin:auxin ratios [145].
RAUNKIAER LIFE FORM :
Phanerophyte
Geophyte
REGENERATION PROCESSES :
Quaking aspen regenerates from seed and by sprouting from the roots
[146]. Stump and root crown sprouting is rare in older trees, but
saplings sometimes sprout from the stump and root crown as well as the
roots [123,145].
Vegetative reproduction: Root sprouting is the most common method of
regeneration. Root suckers originate from meristems in the root's cork
cambium and can develop anytime during secondary growth [140]. Saplings
may begin producing root sprouts at 1 year of age [123]. There are
thousands of suppressed shoot primoridia on the roots of most mature
quaking aspen clones. Recently initiated meristems or primordia usually
sprout and elongate more vigorously than older primorida or suppressed
root buds [145]. Root suckering is affected by depth and diameter of
parent roots. In Utah and Wyoming, Schier and Campbell [144] found that
25 percent of sprouts came from roots within 1.6 inches (4 cm) of the
surface, 70 percent from within 3.2 inches (8 cm), and 92 percent within
4.7 inches (28 cm). Compared with parent roots of quaking aspen in the
Great Lakes States, those of quaking aspen in the West were deeper. On
a Utah burn site, high-severity fires increased the depth of the parent
roots from which sprouts originated. Range in diameter of roots
producing sprouts was 0.04 to 3.7 inches (0.1-9 cm). Sixty percent of
suckers grew from roots smaller than 0.4 inch (1 cm) in diameter, 88
percent from roots smaller than 0.8 inch (2 cm), and 93 percent from
roots smaller than 1.2 inches (3 cm) in diameter. On a Wyoming site,
the percentages were 38 percent, 68 percent, and 86 percent,
respectively.
Sprout development is largely suppressed by apical dominance [145].
Closed stands produce a few inconspicuous sprouts each growing season;
the sprouts usually die unless they occur in a canopy gap. When stems
are removed by cutting, burning, girdling, or defoliation, suppressed
primoridia, buds, and shoots resume growth. Best sucker production
follows either a fire that kills all parent trees and brush or other
complete clearing [23]. The number of suckers produced can vary
markedly among clones [7,159], but the potential for suckering is
enormous. Jones [87] indicated that 20,000 to 30,000 sprouts per acre
is typical the first year following top-kill. Natural thinning is heavy
and effective. The least vigourous suckers die within 1 to 2 years.
After 5 to 10 years, most sucker clumps reduce to a single stem [87].
Most stems are overtopped by more vigorous neighbors. Diseases,
insects, browsing mammals, and snow damage also reduce sprout density
[35,87,108]. Bella and De Franceschi [17] reported that in Alberta and
Saskatchewan, stem density averaged 280,000 per hectare at age 2;
190,000 per hectare at age 3; and 80,000 per hectare at age 5.
Seedling establishment: Quaking aspen commonly establishes from seed in
Alaska, northern Canada, and eastern North America. Seedling
establishment is less common in the West, where rainfall is often
followed by dry periods that kill newly germinated seedlings [90]. Even
in the West, however, quaking aspen may establish from seed more
frequently than previously thought. Studies on frequency of seedling
establishment in the West are conflicting. Some researchers found
absolutely no quaking aspen seedling establishment despite diligent
searching [4,5,16]; others reported the presence of only one [51] or a
few [52] seedlings, while still other researchers documented the
presence of hundreds of seedlings [7,90,97,167]. Only since the
stand-replacement fires of the late 1980's have researchers used
permanent plots to monitor quaking aspen seedling establishment and
survival in the West. Data from one such study are summarized after the
following discussion of sexual reproduction in quaking aspen.
Sexual reproduction: The staminate-pistillate ratio of adult clones is
1:1 in most localities, although it may be as high as 3:1 or more [117].
Some clones alternate between staminate and pistillate forms in
different years, or produce various combinations of perfect, staminate,
and pistillate flowers [50]. Quaking aspen first flowers at 2 to 3
years. Minimum tree age for production of large seed crops is 10 to 20
years, and maximum seed production occurs at about 50 years of age. In
Utah, one 23-year-old tree produced an estimated 1.6 million seeds in
one spring [123]. There are 3- to 5-year intervals between heavy seed
crops [55,102,110,148]. Seeds disperse a few days after they ripen.
Dispersal lasts 2 to 3 weeks [123]. The plumose seeds are dispersed by
wind for distances of 1,600 feet (500 m) to several miles with heavy
winds. Seeds also disperse by water, and can germinate while floating
or submerged [54]. Viability of fresh seed is good; germination of 80
to 95 percent is reported under laboratory conditions [103,109,142].
Viability lasts 2 to 4 weeks under favorable conditions of low
temperature and humidity [123], but seed loses viability rapidly under
less than optimum conditions [54,171].
Optimum conditions for germination and seedling survival include a moist
mineral seedbed with adequate drainage, moderate temperature, and
freedom from competition [104]. In various collections, seeds have
germinated at temperatures from 32 to 102 degrees Fahrenheit (0-39 deg
C), with germination sharply reduced from 35 to 41 degrees Fahrenheit
(2-5 deg C) and progressively curtailed above 77 degrees Fahrenheit (25
deg C) [54,172]. Quaking aspen seed from northern Utah showed optimal
germination between 59 and 68 degrees Fahrenheit (15-20 deg C), and had
no light requirement. Seeds germinated best on the soil surface, with
emergence decreased by shallow burial [104]. Burned or scarified soil
is an excellect seedbed [61]; litter provides the poorest seedbed. The
primary root grows slowly the first few days following germination, and
during this critical period the seedling depends upon a brush of hairs
to absorb water and anchor the plant [123]. Minor disturbances can
uproot surface-germinated seedlings, and a drying seedbed can rapidly
desiccate seedlings [104].
Seedlings may reach 6 to 24 inches (15-61 cm) in height by the end of
their first year, and roots may extend 6 to 10 inches (15-25 cm) in
depth and up to 16 inches (41 cm) laterally. Roots grow more rapidly
than shoots; some seedlings show little top-growth until about their
third year [23]. During the first several years, natural seedlings grow
faster than planted seedlings but not as fast as sprouts. High
mortality characterizes young quaking aspen stands regardless of origin.
In both seedling and sprout stands natural thinning is rapid. Stems
that occur below a canopy die within a few years [123].
Seedling study: Kay [90] documented postfire quaking aspen seedling
establishment following 1986 and 1988 fires in Grand Teton and
Yellowstone National Parks, respectively. He found seedlings were
concentrated in kettles and other topographic depressions, seeps,
springs, lake margins, and burnt-out riparian zones. A few seedlings
were widely scattered throughout the burns. In Grand Teton National
Park, establishment was greatest (950-2,700 seedlings/ha) in 1989, a wet
year, but hundreds to thousands of seedlings established each year
despite drought conditions in 1986-1988 and 1990-1991. Seedlings
surviving past one season occurred almost exclusively on severely burned
surfaces. In Grand Teton National Park, where seedlings were monitored
for several years, surviving seedlings were associated with bare mineral
soil, ash, and the absence of competing vegetation. In both Parks, 100
percent of seedlings were browsed, and mean heights of seedlings at
postfire year 5 (Grand Teton) and postfire year 3 (Yellowstone) were
nearly equal to mean heights at postfire year 1. During the same
period, 0 percent of lodgepole pine seedlings were browsed. Kay
predicted that long-term survival of quaking aspen seedlings will be
low. Most seedlings established on depressions that are subject to
spring flooding. Since quaking aspen does not tolerate standing water,
seedlings on depressions such as kettles and lake margins will probably
die in the first prolonged flood. At postfire year 5, quaking aspen
seedlings in Grand Teton National Park attained only 5 percent more
height growth than attained in the first postfire year. In contrast,
lodgepole pine seedlings had increased in height by an average of 176
percent.
SITE CHARACTERISTICS :
Quaking aspen occurs on a wide variety of sites [40,111]. It grows on
moist upland woods, dry mountainsides, high plateaus, mesas, avalanche
chutes, talus, parklands, gentle slopes near valley bottoms, alluvial
terraces, and along watercourses [40,109,158,166].
Climate: Climatic conditions vary widely over the range of quaking
aspen, especially minimum winter temperatures and annual precipitation.
Generally, quaking aspen occurs where annual precipitation exceeds
evapotranspiration. In Alaska and northwestern Canada, quaking aspen is
common in the boreal zone and extends into the warmest, frost-free sites
of the permafrost zone. At the eastern edge of quaking aspen's range,
climate is humid, with snowfall exceeding 120 inches (3,050 mm) per
year. The southern limit of quaking aspen distribution in the East is
roughly delinated by the 75 degree Fahrenheit (24 deg C) mean July
temperature isotherm. In the central Rocky Mountains, altitude plays an
important role in quaking aspen distribution. The lower limit of its
range coincides with a mean annual temperature of 45 degrees Fahrenheit
(7 deg C) [123].
Soils: Quaking aspen grows on soils ranging from shallow and rocky to
deep loamy sands and heavy clays. Good quaking aspen sites are usually
well drained, loamy, and high in organic matter and nutrients [123].
Cryer and Murray [36] stated that stable quaking aspen stands are found
on only one soil order - mollisols - and a few soil subgroups of which
Agric Pachic Cryoborolls and Pachic Cryoborolls are dominant. The best
stands in the Rocky Mountains and Great Basin are on soils derived from
basic igneous rock such as basalt, and from neutral or calcareous shales
and limestones. The poorest stands are on soils derived from granite.
In the Great Lakes States, the best stands occur in lime-rich, gray
glacial drift [123].
Elevation: Quaking aspen spans an elevational range from sea level on
both coasts to 11,500 feet (3,505 m) in northern Colorado. At its
northern limit, quaking aspen is found only up to 3,000 feet (910 m). In
Baja California, it does not occur below 8,000 feet (2,440 m). In
Arizona and New Mexico is is most abundant between 6,500 and 10,000 feet
(1,980-3,050 m); in Colorado and Utah, it occurs about 1,000 feet (300
m) higher. At either either of its elevational limits, quaking aspen is
stunted. At its lower limit, it grows as a scrubby tree along streambanks;
at high elevations, its stems are bent or prostrate [123].
Aspect: In Alaska and western Canada, quaking aspen grows best on south
to southwesterly exposures. It is common on all aspects in the West,
except in the Southwest, where it is most common on northern aspects.
In the prairie provinces of Canada, particularly on the prairie-woodland
interface, quaking aspen occurs on cooler north and east slopes, and in
depressions [123].
SUCCESSIONAL STATUS :
Quaking aspen is shade intolerant and cannot reproduce beneath its own
canopy [23,40,98,123,126]. Beyond that, there is no single, generalized
pattern of succession in quaking aspen. Quaking aspen is seral to
conifers in most of its range in the West, and in some portions of its
eastern range. In the East, quaking aspen is also replaced by hardwoods
[23,98]. In the Great Lakes States, successional trends are toward
northern hardwoods, spruce-fir, ash-elm (Fraxinus-Ulmus spp.), oak
(Quercus spp.), swamp conifers, and pine (Pinus spp.) types, in
decreasing order of importance [23]. Where it is seral, quaking aspen
usually persists as a minor tree in late seral stages [98].
The canopy closes rapidly in young aspen stands [126]. A quaking aspen
stand in Ontario closed and reached maximum development (foliage/unit
area of soil surface) in 4 years [127,128]. If quaking aspen does not
remain stable, rate of succession to other species varies with with
soil, site, and invading species [71]. Mueggler [112] stated that
succession to conifers may occur in a single generation, or take longer
than 1,000 years. Harper [72] found that in central Utah, quaking aspen
succeeded to conifers in 75 to 100 years on sandstone soils. On
limestone or alluvial soils, succession to conifers took 140 years or
more.
Quaking aspen is apparently stable on some sites. On some former pine
stands in the East, extensive clearcutting of the conifer overstory has
removed the pine seed sources. Quaking aspen has formed an apparently
stable overstory on many of these sites [24]. Quaking aspen stands are
also considered stable in parts of Canada and the western United States
[71]. Some stands, however, remain stable for decades but eventually
deteriorate. Deteriorating stands are often succeeded by conifers, but
shrubs, grasses, and/or forbs gain dominance on some sites [71].
Succession to grasses and forbs is more likely on dry sites and is more
common in the West than in the East [126].
Quaking aspen readily colonizes after fire, clearcutting, or other
disturbance [123]. In Emigrant Wilderness Area, California, red fir
(Abies magnifica) stands on north slopes have converted to quaking aspen
after fire [66]. In the Great Lakes States, quaking aspen has
regenerated on cut/burned sites through sprouting and seedling
establishment, becoming the dominant forest cover type [23].
SEASONAL DEVELOPMENT :
Quaking aspen catkins elongate before the leaves expand. In New
England, catkins appear in mid-March to April; in the central Rockies,
flowering occurs in May to June. Sustained air temperatures above 54
degrees Fahrenheit (12 deg C) for about 6 days apparently trigger
flowering [55,123]. At high elevation, trees may flower before snow is
off the ground [5]. Female trees generally flower and leaf out before
male trees. Local clonal variation produces early- and late-flowering
clones of either sex, however. Catkins mature in 4 to 6 weeks (usually
in May or June). Branches usually leaf out from early May to June
[123]. Seed dispersal in the Great Lakes States occurs from early May
to mid-June, beginning earliest on protected sites and in southern
portions of the region [23].
FIRE ECOLOGY
SPECIES: Populus tremuloides | Quaking Aspen
FIRE ECOLOGY OR ADAPTATIONS :
Fire adaptations: Quaking aspen is highly competitive on burned sites
[46]. Even where quaking aspen was a barely detectable component of the
prefire vegetation, it often dominates a site after fire. Quaking aspen
has adapted to fire in the following ways [41].
1. The thin bark has little heat resistance, and quaking aspen is
easily top-killed by fire.
2. Root systems of top-killed stems send up a profusion of sprouts for
several years after fire.
3. Sprouts grow rapidly by extracting water, nutrients, and
photosynthate from an extant root system, and may outcompete other woody
vegetation.
4. Following a fire, a new, even-aged quaking aspen stand can develop
within a decade.
5. In contrast to most trees, quaking aspen is self-thinning. Without
intervention, a mature forest of healthy trees can develop from dense
sprouts.
Fire releases sprout primorida on roots from hormonally controlled
growth inhibition; removes canopy shade; and blackens the soil surface,
increasing heat absorption. Increased soil temperatures aid sprout
production [22,83]. On cold sites, quaking aspen may be unable to
sprout until soil temperatures rise after fire [83].
Quaking aspen is able to naturally regenerate without fire or cutting on
some sites [123], but fire may be required for regeneration on others.
There are areas in Jackson Hole, Wyoming, where ungulate browsing has
been light, both historically and recently, yet stems have not attained
tree size since extensive fires in the 1800's [69].
Fuels and fire behavior: Fuels are usually more moist in quaking aspen
stands than in surrounding forest. Crown fires in coniferous forests
often drop to the surface in quaking aspen, or may extinguish after
burning into quaking aspen only a few meters [19,55,138]. Quaking aspen
stands often act as natural fuelbreaks during wildfires [55], and fires
sometimes bypass quaking aspen stands surrounded by conifers [138]. In
an analysis of fires in quaking aspen in National Forests of the
Intermountain West (USFS Regions 2, 3, and 4) from 1970 through 1982,
Bevins [19] reported that wildfires that burned thousands of acres
during extreme weather conditions usually penetrated less than 65 feet
(20 m) into quaking aspen. Managers he interviewed used the terms
"abestos type" and "firebreak" to describe quaking aspen stands. Bevins
reported that mixed quaking aspen-conifer types such as those on the
northern Kaibab and Dixie National Forests did sustain fires, however,
and burned substantial amounts of quaking aspen. Throughout all three
Regions, a relatively few, large fires (>100 acres burned) accounted for
93.2 percent (or 1.12 million acres) of all quaking aspen burned.
Fire history: Before and during the mid-nineteenth century, fires were
apparently more frequent, and larger acreages of quaking aspen and
quaking aspen-conifer mixes burned, than any time since. A large
majority of the quaking aspen stands in Jackson Hole, Wyoming, date from
fires between 1850 and 1890 [69]. In central Utah, Baker [5] and
Meinecke [106] found few quaking aspen fire-scarred later than 1885.
Earlier fire scars were common and showed a 7- to 10-year fire
frequency. Since quaking aspen is fire-sensitive, the fires were
probably of low severity. Extensive sampling of quaking aspen in
Colorado found few fire scars dating later than about 1880 [37].
These data indicate that there has been a great reduction of fire
rejuvenation of quaking aspen in the West since about 1900. Extensive
young stands of quaking aspen are uncommon in the West [65,151,46].
Conifers now dominate many seral quaking aspen stands. Probable
contributing facters are:
1. highly effective direct control of wildfires in the last 50 years,
especially in the quaking aspen type [46],
2. reduction of fine fuels in quaking aspen/grass and quaking
aspen/forb types due to grazing [28,46], and
3. cessation of deliberate burning by Native Americans [9,68,80].
Ungulates, fire, and quaking aspen: In most areas, ungulate browsing is
probably not a major factor restricting postfire quaking aspen
regeneration. Quaking aspen has increased in importance in the East
depsite browsing pressure from large white-tailed deer populations. In
many areas of the United States, elk populations impact quaking aspen
very little. Browsing elk had no significant impact on quaking aspen
sprout density after wildfire in New Mexico [115]. In some areas,
however, fire suppression coupled with heavy ungulate browsing has
reduced quaking aspen regeneration. Failure of some stands in the Great
Lakes States to regenerate has been attributed to overbrowsing of
sprouts by white-tailed deer [145]. Overbrowsing has particularly been
noted in northwestern Wyoming, in Yellowstone and Grand Teton National
Parks and the Bridger-Teton National Forest. Elk are the primary
browsers of quaking aspen in this area, although where moose populations
are high, moose have also removed considerable quaking aspen
regeneration. Historic narratives and photographic evidence suggest
that ungulates were a major biotic influence on quaking aspen in this
region during the the exploration and settlement periods. However,
fires were extensive during this period, so postfire sprouting of
quaking aspen and growth of palatable grasses, shrubs, and herbs,
probably produced a forage supply that dispersed browsing ungulates
sufficiently for quaking aspen to regenerate [69].
Coring of old quaking aspen stems in Yellowstone National Park showed
that most live, large quaking aspen established in a brief period
between the 1870's and 1880's: a period of severe fires followed by
above-normal precipitation. Elk, moose, and beaver populations were at
a historic low, and some wolves were present. Neither this combination
of conditions nor significant quaking aspen regeneration has occurred
since then. Elk populations were low in the 1950's and 1960's, but
fires were suppressed and the climate was dry. In the 1910's, there
were numerous elk and beaver and few fires. After the 1988 fires, elk
numbers were high and climatic conditions were dry. In this region,
even large-scale burning does not seem sufficient for quaking aspen
regeneration [69,90,137].
Prairie: Frequent fires on prairies and plains grasslands historically
helped control quaking aspen invasion [30]. Fire may have been only one
of several factors controlling quaking aspen, however. Drought [76] and
ungulate browsing may have worked in conjunction with fire to curtail
woody plant invasion. Fire alone may not control quaking aspen spread
[32]. Anderson and Bailey [2] reported that 24 years of annual spring
burning checked quaking aspen invasion onto tallgrass prairie, but
actually increased the number and cover of quaking aspen sprouts in the
area. Elk Island National Park, Alberta, was described by early
settlers as a grassland with scattered quaking aspen groves. By 1895,
extirpation of bison and severe reduction of other ungulates was
followed by expansion of quaking aspen. Bison were reintroduced with
Park establishment, but fire was not. Ungulate populations rose rapidly
and were culled in the 1930's and 1950's. Grassland expanded with the
ungulates, while quaking aspen expanded when culling occurred [21].
POSTFIRE REGENERATION STRATEGY :
Tree with adventitious-bud root crown/soboliferous species root sucker
Initial-offsite colonizer (off-site, initial community)
FIRE EFFECTS
SPECIES: Populus tremuloides | Quaking Aspen
IMMEDIATE FIRE EFFECT ON PLANT :
Small-diameter quaking aspen is usually top-killed by low-severity
surface fire [88]. Brown and DeByle [26] found that as dbh increases
beyond 6 inches (15 cm), quaking aspen becomes increasingly resistant to
fire mortality. Large quaking aspen may survive low-severity surface
fire, but usually shows fire damage [26,94]. Moderate-severity surface
fire top-kills most quaking aspen, although large-stemmed trees may
survive. Some charred stems that survived low- or moderate-severity
fire initially have been observed to die within 3 or 4 postfire years.
Severe fire top-kills quaking aspen of all size classes.
Moderate-severity fire does not damage quaking aspen roots insulated by
soil. Severe fire may kill roots near the soil surface or damage
meristematic tissue on shallow roots so that they cannot sprout. Deeper
roots are not damaged by severe fire and retain the ability to sucker
[69,160,143,146].
Mortality does not always occur immediatedly after fire. Sometimes buds
in the crown will survive and leaf out prior to the death of the tree
[26]. Brown and DeByle [26] reported that quaking aspen trees died over
a 4-year period following fires in Wyoming and Idaho, although most
individuals succumbed by the second postfire year. Even when quaking
aspen is not killed outright by fire, the bole may be sufficiently
damaged to permit the entrance of wood-rotting fungi [94]. According to
Jones and DeByle [88], basal scars which lead to destructive heart rot
can be made on even good-sized aspen by "the lightest of fires." Basal
fire scars may also permit entry of borers and other insects which can
further weaken the tree [23].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT :
Fire may kill (as opposed to top-kill) a deteriorating stand of quaking
aspen. A deteriorating stand on the Sweetwater drainage of the Wind
River Mountains, Wyoming, failed to sprout following a 1963 wildfire.
However, another 1963 wildfire in the Wind River Mountains, near
Pinedale, had the opposite effect on a deteriorating stand of quaking
aspen. Although the site was considered poor for quaking aspen due to
dry, sandy soil, fire only top-killed the stand. Browsing pressure on
sprouts was light, and postfire stocking was "more than adequate" for
regeneration [69].
The position of an individual tree on a slope, or within a stand, can
influence the degree of damage caused by fire. Even when damaged, trees
located near the boundaries of a fire can often maintain a live crown.
These peripheral trees may receive food supplies from the roots of
unburned neighbors. Quaking aspen on slopes generally show greater
damage than do trees on flatter areas. Flames moving uphill often curl
up the lee side of trees when fanned by upslope wind, charring the stem
further up its bole. The effect of slope is particularly pronounced (up
to 31-44% higher char heights) after fires of higher severity. This
relationship is presented in the following table [26]:
Probability of mortality
________________________
0.90 0.95
________________________
dbh (cm) Average char height -
10 5 12
15 14 21
20 23 30
25 32 39
Uphill char height -
10 6 16
15 19 29
20 31 42
25 44 55
PLANT RESPONSE TO FIRE :
Quaking aspen sprouts from the roots and establishes from off-site,
wind-blown seed after fire [27,123,157]. It is the classic soboliferous
species described by Stickney [157]: a plant that sprouts from
carbohydrate-storing lateral roots (sobols).
Sprouting: Quaking aspen generally sprouts vigorously after fire.
Long-term growth and survival of quaking aspen sprouts depend on a
variety of factors including prefire carbohydrate levels in roots,
sprouting ability of the clone(s), fire severity, and season of fire.
Moderate-severity fire generally results in dense sprouting. Fewer
sprouts may be produced after severe fire. Since quaking aspen is
self-thinning, however, sprouting densities are generally similar
several years after moderate and severe fire. A low-severity surface
fire may leave standing live trees that locally supress sprouting,
resulting in an uneven-aged stand [12,13,28,123].
Quaking aspen burned in spring generally sprouts later in the growing
season and again the following year. Fires in mid-growing season
generally result in late-season sprouting. Quaking aspen burned in late
summer or fall usually sprouts the next spring [28].
Predicting postfire sprouting: Appyling prescribed fire in exclosures
in Yellowstone National Park, Renkin and Despain [133] found that root
biomass can be estimated from basal area, and both can be used to
predict local response of quaking aspen to burning. Sprout biomass
produced in postfire year 1 was positively correlated (r2=0.90, p=0.013)
with both prefire basal area and root biomass. On average, 11.5 metric
tons per hectare of root mass were required to produce 0.1 metric ton
per hectare of sprouts. Average sprout height was positively correlated
with basal area and root biomass (r2=0.85, p=0.004). On average, 25
square meters per hectare of basal area and/or 19 metric tons per
hectare of root biomass were required to produce 0.5 meter of sprout
growth.
Examples of sprouting: After the 1988 fires in Yellowstone National
Park, percentage of sprouts produced in spring, 1989, was significantly
higher (p=0.030) in burned stands (mean 82%) than on unburned stands
(mean 60%). The percentage of sprouts in fall, 1989, was also higher
(p=0.103) on burned stands (mean 82%) than in unburned stands (mean
65%). In spring 1990, sprout density averaged 80,000 stems per hectare
in burned stands and 27,000 stems per hectare in unburned stands. By
fall 1991, density was 38,000 stems per hectare in burned and 25,000
stem per heactare in unburned stands, respectively. Mean heights were
9.6 inches (24 cm) in spring 1990 and 10.8 inches (27 cm) in spring
1991. Browsing intensity was much higher in winter and spring (45-55%
of sprouts browsed) than summer and fall (5-10%). There were no
significant differences in browsing among burned stands, unburned stands
adjacent to burned stands, and remote unburned stands: Sprouts were
heavily browsed in all stand types [137].
Birch-aspen: Following a 1944 summer wildfire in Maine, quaking aspen
and paper birch sprouted vigorously, forming a dense stand. In 1951,
there were 40,000 to 45,000 stems (both spp.) per acre. Quaking aspen
dominated the stand; it averaged 20 feet (6 m) in height while paper
birch averaged only 6 feet (1.8 m) [96].
For further examples of quaking aspen sprouting response after fire,
refer to the FIRE CASE STUDIES section. Cases from Arizona, New Mexico,
Colorado, Wyoming, Minnesota, and Alberta are presented.
Seedling Establishment: Fire exposes mineral soil, which is an
excellent seedbed for quaking aspen [61]. Quaking aspen seedlings have
been noted following severe fire in Canada. Six years after fire in
northeastern Wisconsin, quaking aspen seedlings composed 20 to 35
percent of seedlings of all species present on the burn [79]. Kay [90]
reported good seedling establishment following 1986 fires in Grand Teton
National Park and 1988 fires in Yellowstone National Park. Height
growth was negligible, however, due to ungulate browsing. Density,
height, and ungulate use of quaking aspen seedlings on the Yancy's Hole
Burn, Yellowstone National Park, were [90]:
_____________________________________________________________________
Transect # Year Number/ha % browsed Mean height (cm)
1 1989 177,202 -- 62
1991 32,154 100 50
2 1989 141,362 -- 60
1991 46,148 100 57
3 1989 109,522 -- 53
1991 16,660 100 75
__________________________________________________________________
Mean 1989 142,695 -- 58
1991 31,654 100 47
Renkin and others [134] are conducting a similar seedling study on
forested and nonforested sites in Yellowstone National Park; only
preliminary data are available at this time. They found that quaking
aspen seedlings were concentrated on wet microsites but widely scattered
on other site types. In 1989, quaking aspen seedling density on 14
plots ranged from 0.6 to 1,014 per square meter; average height ranged
from 2.3 to 11.1 inches (mean=5.1 inches) (5.7-27.8 cm, mean= 12.8 cm).
Quaking aspen seedlings were two to four times taller than lodgepole
pine seedlings on forested plots. In 1990, all plots had persistent
quaking aspen seedlings; in some cases the stem had died back but the
1-year-old roots had produced suckers. Density of surviving seedlings
ranged from 0.05 to 332 per square meter. Average heights had
increased, ranging from 3.6 to 15.6 inches (mean=7.8 in) (9-39 cm,
mean=19.4 cm). Quaking aspen seedlings on fenced plots averaged 12
inches (30 cm) in height; seedlings on unfenced plots averaged 5.36
inches (13.4 cm). Seedling survival was significantly greater (p=0.004)
on forested than nonforested plots. Survival was also influenced by
presence of ungulates, spring flooding, disease, and intraspecific
competition. Ungulate presence negatively influenced seedling survival
on unfenced plots (r=0.97, p=0.004). Plots submerged in spring showed
high seedling mortality. A fungus (Venturia tremulae) also contributed
to seedling death or dieback [134].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE :
NO-ENTRY
FIRE MANAGEMENT CONSIDERATIONS :
Prescribed fire is recommended for quaking aspen [2,25,123,143].
Currently, an estimated 600 acres (240 ha) of quaking aspen burns per
year in the Intermountain Region. At that rate, it will require 12,000
years to burn the entire quaking aspen type in that Region. It is
likely that seral quaking aspen will be replaced by conifers; stable
quaking aspen stands may become less productive [46]. In many areas of
the West, quaking aspen stands have lived longer than they did prior to
fire exclusion, and many stands are in a state of decline due to
advanced age [62]. Gruell and Loope [69] found that in Jackson Hole,
Wyoming, quaking aspen stands begin to deteriorate after about 80 years.
Houston [80] stated in 1973 that quaking aspen in Yellowstone National
Park were primarily large trees ranging from 75 to 120 years of age.
Applying fire: Prescribed fire is often difficult to apply in quaking
aspen stands because of the prominence of live fuels and often sparse
distribution of fine dead fuels [25]. Even if fuels are plentiful, they
are usually too moist to burn easily. Prescribed fire may be possible,
however, when live vegetation cures enough to contribute to fire spread
rather than hinder it. The combination of dry weather and cured fuels
occurs most often in early spring, late summer, and fall [131,138]. The
forest floor of a quaking aspen stand immediately after snowmelt is
covered by matted, cured surface vegetation and deciduous leaf litter.
Before leaf-out this mat is directly exposed to drying by wind and sun,
which increase fuel temperature and decrease fuel moisture. Without
rain, the withered leaves in the litter begin to curl, resulting in a
more favorable fuelbed for combustion and heat transfer. In Alberta,
these moderately severe, early season burning conditions can persist
from snowmelt until the first week in June [131].
In most years, leaf fall and autumn precipitation coincide, making fall
burning difficult. If September and October are dry, however, burning
may be possible. Surface fuels are dead and sometimes frozen, with a
continuous layer of loosely packed leaves, making quaking aspen more
flammable than at any other time of year [138].
Live fuel moisture varies greatly between understory species throughout
the growing season, but can be estimated well enough to determine when
to light prescribed fires. Brown and others [25] estimated that when
herbaceous vegetation is the primary fine fuel, at least 50 percent
curing is needed to sustain fire spread. Less than 50 percent curing
may be sufficient in stands with substantial conifers. Brown and
Simmerman [28] provide a method for appraising fuels and flammability in
quaking aspen to assist managers in choosing when to apply prescribed
fire and help determine proper conditions for burning. Five fuel types
in 19 community types common in the Intermountain West are presented,
accompanied by color photographs.
Prescriptions: Aspen parkland and northern forest - Bailey [174,175]
found that in Alberta, prescribed burning in quaking aspen forests and
parklands in spring was usually not successful above relative humidity
of 35 to 40 percent. He recommended that prescribed burning be
conducted 8 to 10 drying days after snowmelt, when air temperature is at
least 64 degrees Fahrenheit (18 deg C), relative humidity is less than
30 percent, and 3.3-foot (10-m) open winds are 5.4 to 21 miles per hour
(9-35 km/hr).
Bailey and Anderson [173] reported that in central Alberta, quaking
aspen forest in a grassland-shrub-quaking aspen forest mosaic was the
most difficult of the three vegetation types to prescribe burn. With
spring burning, backfires consistently gave poor results, frequently
going out within a few feet of ignition and yielding a maximum
temperature of only 550 degrees Fahrenfeit (288 deg C). Headfires were
hotter but gave variable results. Most headfire temperatures ranged
from 700 to 900 degrees Fahrenheit (371-482 deg C), but 14 percent were
in excess of 1,112 degrees Fahrenheit (600 deg C). Fire and fuel data
from the quaking aspen sites follow.
________________________________________________
| fire temperature 393 +/- 28* (deg C) | | total fuel 13,436 +/- 354 (kg/ha) | | ground fuel 11,704 +/- 337 (kg/ha) | | standing woody fuel 1,732 +/- 181 (kg/ha) |
|______________________________________________|
*standard error of the mean (SEM)
Perala [119] recommended this prescription for burning quaking aspen
slash in the Great Lake States:
______________________________________________________________________
Months for burning dormant season
(all but June, July, & August)
Fuel model* D
Air temperature > 65 degrees Fahrenheit (18 deg C)
Relative humidity < 35%
Ignition component* 40-50
Energy release component* 14-17
Spread component* 4-7
Burning index* 13-21
Wind** 2.5-5 m/s
Number of days with less
than 2.5 mm rain > 5
______________________________________________________________________
*from the National Fire-danger Rating System [176]
**measured 20 ft. above ground, or at average height of vegetation
cover, averaged over at least a 10-minute period
Canadian Forest Fire Behavior Prediction (FBP) System : Alexander and
Maffey [1] provide examples for predicting fire spread rate, fuel
consumption, and frontal intensity in quaking aspen types using the FBP
System.
Forage quality and fire: Three burned quaking aspen/shrub/tall forb
communities on the Caribou National Forest, Wyoming, showed increased
forage quality (better Ca:P ratios, higher elk digestibilty, and higher
crude protein and P levels) than adjacent unburned sites during the
first postfire year. By the second postfire year, there were no
significant differences between forage quality on burned and unburned
sites. Shrubs on the unburned sites were above browse level throughout
the study period, however, while shrubs on the burned site were still
accessible to elk in the second postfire year [47].
FIRE CASE STUDIES
SPECIES: Populus tremuloides
| Quaking Aspen
- 1st CASE STUDY:
WY/Sprouting density and elk use after prescribed fire
- 2nd CASE STUDY:
CO/Aspen survival & sprouting after prescribed fire
- 3rd CASE STUDY:
MN/Aspen productivity after harvest & repeat prescribed fire
- 4th CASE STUDY:
Central AB/Overstory mortality after repeat spring prescribed fire
- 5th CASE STUDY:
NM/sprouting after wildfire in spruce-fir/postfire browsing
- 6th CASE STUDY:
AZ/Prescribed fire in a quaking aspen/bunchgrass type
- 7th CASE STUDY:
Central AB/Prescribed fire temperatures & effects in aspen forest
WY/Sprouting density and elk use after prescribed fire
Bartos, D. L.; Brown, J. K.; Booth, G. D. 1994 [10]
Bartos, D. L.; Mueggler, W. F. 1979 [12]
Bartos, D. L.; Mueggler, W. F. 1981 [13]
Bartos, D. L.; Mueggler, W. F.; Campbell, R. B., Jr. 1991 [14]
Basile, J. V. 1979 [15]
Brown, J. K.; Debyle, N. V. 1987 [26]
Howard, Janet L. 1996
summer (Aug. 29, 1974)/low-severity to severe
The study site, Breakneck Ridge, is located on the upper drainage of the
Gros Ventre River of the Bridger-Teton National Forest, approximately 29
miles (48 km) northeast of Jackson, Wyoming [12].
The landscape was a mosaic of quaking aspen (Populus tremuloides),
conifer (mostly subalpine fir [Abies lasiocarpa]), big sagebrush
(Artemisia tridentata), and grassland communities. Quaking aspen groves
were mostly on southwesterly to northwesterly slopes. Subalpine fir was
invading on northerly aspects [10,13]. Some decandent quaking aspen
clones were being replaced by big sagebrush/grass. Quaking aspen sucker
density was approximately 14,000 per hectare. Suckers were mostly less
than 1 meter tall and suppressed by elk and moose browsing [13].
The shrub layer of the quaking aspen groves consisted of shrubby
cinquefoil (Pentaphylloides floribunda), Wood's rose (Rosa woodsii),
mountain snowberry (Symphoriocarpos oreophilus), and quaking aspen
sprouts. Slender wheatgrass (Elymus trachycaulus), fringed brome
(Bromus ciliatus), sticky geranium (Geranium viscosissimum), lodgepole
lupine (Lupinus parviflorus), woodland strawberry (Fragaria vesca),
fireweed (Epilobium angustifolium), and Fendler's meadowrue (Thalictrum
fendleri) were common in the herbaceous understory [10,12].
Grazing use: The study site lies along an elk migration route. Elk use
of the area is severe in fall, winter, and spring. Cattle graze the
area three summers out of four on a rest-rotation system [10].
Plots: Ten quaking aspen clones (0.8 to 2 acres [2-5 ha] each) were
selected for study. Nine clones were targeted for burning. A firebreak
was established around the most southerly clone for an unburned control.
Four permanent 10 X 10-meter macroplots were established in each clone,
for a total of 40 macroplots [10,13].
The fire was conducted during the growing season. The flowering period
was over and quaking aspen was fully leaved [12].
Aspect on the study sites is northwest to northeast, with a 14 to 42
percent slope. Elevation is 7,897 to 8,263 feet (2,393-2,504 m). Aspen
site index (80 yr) was 40 to 65 [14].
The primary purpose of the prescribed fire was to produce more quaking
aspen suckers than elk could consume, and thus perpetuate the quaking
aspen stands [10]. The area was burned on August 29, 1974. Weather
conditions were [13]:
air temperature: 77 degrees Fahrenheit (25 deg C)
winds: 7.8-19.2 mi/hr (13-32 km/hr), gusty
relative humidity: 18%
fuel moisture: 10-45%
The area did not burn uniformly and a patchwork of fire severities
resulted. Portions of the nine prescribed burned macroplots did not
burn; other portions were lightly, moderately, or severely burned. This
was attributed to differences in amount of dry fuel on the ground and
differences in moisture content of duff and understory vegetation due to
slight differences in exposure [13].
Of the 36 burned macroplots (4 were controls), 11 were lightly burned,
13 were moderately burned, and 12 were severely burned. Light burns
were defined as those removing less than 21 percent of litter and duff;
moderate burns removed 21 to 80 percent, and severe burns removed 81 to
100 percent of litter and duff [13].
More than 90 percent of the quaking aspen overstory was killed on
severely burned sites. Top-kill on moderately burned sites was less than
90 percent [12].
Prescribed fire stimulated quaking aspen sucker production relative to
the control. Sucker production peaked in postfire year 2. By postfire
year 3, suckers on burned sites had thinned to about 30,000 per hectare
as opposed to 17,000 per hectare on the control. After 3 years, both
moderately and severely burned sites supported approximately the same
number of sprouts [12].
Although fire stimulated sucker production, elk use of the suckers was
heavy. Quaking aspen sucker densities 6 years after fire ranged from
4,300 to 10,300 per hectare for the three fire severities:
approximately the same as before the fire. At postfire year 12,
densities ranged from 1,500 to 2,400 suckers per hectare, which was 20
to 38 percent less than prefire densities. The control area had 5,150
suckers per hectare in 1986 compared to 8,500 per hectare that occurred
prior to treatment. The 39 percent reduction of suckers on the control
was attributed to elk use [1].
Average quaking aspen sprout density for 6 sample years follow. Mean
values are on top and standard error of the mean (SEM) are shown below
[10].
________________________________________________________________________
Fire
severity 1974
1975 1976
1977 1980 1986
---------------------------------Number/ha------------------------------
Control 8,500
18,625 16,750 18,625
12,250 5,150
3,373 4,023
3,455 2,585
3,099 1,981
Low
4,000 7,727 15,727
8,636 4,318 1,518*
1,452 2,322
4,093 2,140
1,995 686
Moderate 5,962 18,692
30,692 20,154 9,654 1,854*
1,535 5,121
8,528 5,230
2,376 712
Severe
8,417 7,333* 36,458 21,792
10,292 2,400
1,633 2,831
7,114 3,889
2,839 589
__________________________________________________________________
*Fire severity means followed by an asterisk are significantly different
(p<0.10) from the control.
After 12 years, the objective of producing more quaking aspen suckers
than elk could consume was not met. Enough suckers were produced
initially to reestablish the quaking aspen stands; however, most suckers
were eliminated or severely suppressed by heavy elk browsing. (Cattle
seldom browsed the quaking aspen suckers and appeared to have little
impact on quaking aspen.) Bartos, Brown, and Booth [10] have questioned
the use of prescribed fire in areas subject to heavy ungulate use. In
this case, rather than rejuvenate the quaking aspen stands, fire may
have sped up their deterioration.
Differences in browsing by clone: Postfire browsing varied by clone.
Elk browsing in the winter of 1976 - 1977 averaged 44 percent of current
growth and reduced average height of suckers by 28 percent. In 1977,
height of tagged suckers had increased an average of only 1 percent over
the previous year. Growth rates of 20 tagged quaking aspen suckers were
[15]:
____________________________________________________
|
| Height change from
| Winter
1976-1977 | summer
1976-summer 1977
Clone|______________________|_________________________
| Mortality | Utilization
| Height | Unprotected |
Protected in
|
| current | reduction
|
| exclosures
|
| growth |from
summer|
|
--------------------------------Percent-------------------------------------------------
1
5
33
28
14
2
5
46
33
-6
3
0
38
24
0
4
20
68
49
-25
16
5
5
58
37
10
6
5
63
37
-10
7
5
17
15
10
8
0
22
13
4
9
10
64
34
-20
17
10*
15
34
10
14
7
Average
7
44
28
1
13
____________________________________________________
*unburned control clone
There were no significant differences between sucker density on sites
with different burn severities [10]. In theory, moderate-severity fire
should produce the greatest amount of suckering, but this does not
always occur in practice because factors other than fire severity, such
as parent stand vigor, genetic differences in clones, and competition
with other vegetation also affect postfire sprouting response [26].
Understory response: Prescribed fire stimulated understory production.
Increase in production was still evident 12 years after fire. In 1986,
understory production was approximately 2,190 kg/ha on severely burned
sites; 2,140 kg/ha on moderately burned sites; and 2,130 kg/ha on sites
where fire severity was low. This exceeded prefire production by 42,
46, and 23 percent, respectively [10].
|
