Geoscience Reference
In-Depth Information
Vegetation of Yellowstone National Park
About 80 percent of YnP is covered by forest (see
fig.  1.5). the park's forests appear uniform to many
visitors, yet ecologists have identified more than
thirty different forest environments (habitat types
and phases). 20 Lodgepole pine predominates over large
areas, especially on the rhyolite plateaus (see chapter
10). Lodgepole is probably the only tree capable of
thriving on such infertile soils; indeed, without lodge-
pole pine, there might be little or no forest over much
of the park. Some twenty-four habitat types in which
lodgepole pine is a major constituent have been iden-
tified. Some of the distinguishing understory species
include globe huckleberry and bluejoint reedgrass on
relatively moist and fertile sites, with grouse whortle-
berry, pinegrass, and elk sedge on dry and infertile
sites. engelmann spruce and subalpine fir also are com-
mon and in some places dominant, especially on more
fertile substrates derived from andesite or sedimentary
rocks. Whitebark pine is common in high-elevation
forests (fig. 15.5), and Douglas-fir is common in the
foothills (fig. 15.6) . 21 tree-dominated riparian wood-
lands are not common in the park, but where they do
occur, the principal trees are aspen, balsam poplar,
narrowleaf cottonwood, and sometimes Douglas-fir,
engelmann spruce, and lodgepole pine. 22
nonforested land occupies most of the remaining
20 percent of Yn P. 23 Foothill grasslands dominated
by bluebunch wheatgrass and Sandberg bluegrass are
found at low elevations near Gardiner, where annual
precipitation is only about 10 inches. Also found in this
area are desert shrublands dominated by fringed sage,
Gardner saltbush, greasewood, pricklypear cactus, and
winterfat. Meadows at low elevations along the Lamar
River have the introduced Kentucky bluegrass, such as
near the site of the old Buffalo Ranch in the Lamar Val-
ley, along with native species that include Wheeler blue-
grass, sheep sedge, and bearded wheatgrass.
Big sagebrush is found in the Yellowstone and Lamar
river valleys, where large numbers of elk and bison
spend the winter; silver sagebrush and shrubby cinque-
foil are found in meadows where the soils stay wetter
for a longer time, such as in Hayden and Pelican val-
leys (fig. 15.7). Associated plants include idaho fescue,
junegrass, thickspike wheatgrass, and bearded wheat-
Fig. 15.5. Whitebark pine, shown here at the top of Mount
Sheridan in Yellowstone national Park, is the predominant
treeline species in northwestern Wyoming and the northern
Rocky Mountains. in many areas the trees have been killed
during the past two decades by native mountain pine beetles
and the non-native white pine blister rust. elevation 10,308
feet at the summit.
grass. interspersed throughout the subalpine forests are
meadows dominated by tufted hairgrass and a variety
of sedges and forbs.
Several species of sedge are especially common in
fens and wet meadows (see chapters 4 and 5), includ-
ing beaked sedge, Buxbaum's sedge, livid sedge, mud
sedge, northwest territory sedge, slender sedge, and
water sedge. Sphagnum and philontus mosses occur
with sedges in some areas. Wetlands with standing water
have hardstem bulrush and few-flowered spikerush,
with diamondleaf willow and Wolf's willow along the
margin . 24 i in the riparian zone both meadows and shrub-
lands occur. Riparian meadows typically have bluejoint
reedgrass; tufted hairgrass; and other grasses, sedges, and
forbs. Shrublands along the creeks and rivers have alder,
water birch, shrubby cinquefoil, silver sagebrush, and
various species of willow (diamondleaf willow, Geyer's
willow, sage willow, tealeaf willow, Wolf's willow, and
 
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