Geoscience Reference
In-Depth Information
shoots apparently suppress the growth of the smaller
ones below—a case of apical dominance. Aspen stands
burn periodically, at intervals of decades or centuries,
and the thin-barked adult stems are usually killed . 99
However, abundant post-fire sprouting and rapid growth
result in the re-establishment of an aspen grove within
a few decades. chronic heavy browsing on the aspen
sprouts by wild and domestic ungulates can inhibit this
process of aspen regeneration (see chapters 10 and 15) . 100
old landscape photos from the late 1800s and early
1900s commonly show more aspen than is visible in the
same scenes today, suggesting that aspen is declining
in at least some areas. this comparison may be mis-
leading, simply because the late 1800s was a time of
extensive burning throughout the West, and post-fire
aspen probably was exceptionally abundant around
1900, compared with earlier in the nineteenth century
or in previous centuries. thus, aspen abundance at the
beginning of the twentieth century is not necessarily
an appropriate historical benchmark for land manage-
ment. 101 Moreover, photos from other areas show that
aspen cover remained stable or even increased in some
places during the twentieth centur y. 102 Some resource
managers are concerned that twentieth-century fire
exclusion and other factors have led to deterioration of
many aspen groves, as the adult aspen stems gradually
die and are replaced by conifers or shrubs instead of
new aspen sprouts. Aspen shoots can be killed by vari-
ous pathogens, including root rot and canker diseases,
especially if the bark is damaged. this trend of stand
deterioration is especially worrisome if the capacity for
sprouting diminishes as stands age, or if the intensity of
ungulate browsing or beaver cutting is high (see chap-
ters 10 and 15). 103
the first decade of the twenty-first century saw exten-
sive death of aspen trees in Wyoming and across much
of the West, apparently triggered by the severe drought
of 2000-2003. 104 t he patterns and implications of this
mortality event, referred to as sudden aspen decline (SAD),
are discussed in chapter 12. Despite such developments
in aspen forests, there seems little need to be concerned
about aspen extinction. 105 Still, the tree could become
less abundant in some areas as aspen-dominated forests
gradually change to conifer-dominated forests or shrub-
lands. to maintain the current abundance of aspen
forests in the landscape may require more harvesting
of the conifers, more prescribed fires, or reductions in
ungulate numbers.
Mountain Forests and Wildlife
the forest-meadow-wetland mosaic provides essen-
tial habitat for numerous birds and mammals. A few
are found there all year long, such as the blue grouse,
boreal owl, clark's nutcracker, gray jay, red crossbill,
beaver, lynx, marten, red squirrel, snowshoe hare, and
voles. others migrate to the foothills for the winter,
escaping deep snow and colder temperatures, returning
to the mountains in the summer for more reliable for-
age and better hiding cover. elk, mule deer, and cou-
gar are notable examples. Many birds, such as warblers,
thrushes, kinglets, and white-crowned sparrow, migrate
to warmer southern climates for the winter, along with
the few ducks and mergansers that use mountain lakes
and beaver ponds. As noted, some birds and small mam-
mals rely on conifer seed for their food. others feed on
mushrooms or mature insects, or dig out insect larvae
from decomposing wood or the bark of living trees. the
abundance of insects emerging from wetlands provides
food for birds that are agile enough to catch them. even
bears are known to eat moth larvae, which can be abun-
dant under the rocks on talus slopes.
commonly, mountain wildlife is secretive and not
easily observed. As in other ecosystems, the best time
to find them is in the spring, when the birds can be
located by their singing, or during the winter, when
many species congregate in flocks, or footprints can be
observed in the snow. Aspen groves are often identified
as hotspots of biological diversity, perhaps because of
the abundance and diversity of understory plants, the
frequent proximity of aspen to water, and the relative
ease with which cavities can be found or created for
nesting. in all kinds of forest, many animals depend on
dead trees, whether for perches or cavities . 106 For many
species, the juxtaposition of wetlands, meadows of vari-
ous kinds, and forests of different ages and types makes
for the perfect habitat. As always, the landscape mosaic
must be considered, not just a few acres of meadow or
forest.
overall, forests of all kinds cover about 15 percent of
Wyoming and are found primarily in the mountains,
where temperature, moisture, and nutrient conditions
 
Search WWH ::




Custom Search