Geoscience Reference
In-Depth Information
Several studies have shown genetic differentiation over
short environmental gradients in Rocky Mountain
conifers, and aspen groves at high elevations are geneti-
cally different from those in the foothills. 12 consider-
able genetic variability, one aspect of biodiversity, can
be expected in landscapes with rapid spatial and tem-
poral changes.
Vertebrates have an equally diverse range of adap-
tations for surviving in mountain landscapes. Some
migrate in the fall to warmer or less stressful environ-
ments at lower elevations or farther south, minimiz-
ing their exposure to cold temperatures, deep snow,
and food shortages during the winter. other species
survive because of remarkable insulation provided by
fur, fat, and feathers, and because they find or build
insulated shelters, such as in deep snow or under logs.
energy stored during the preceding summer in fatty
tissue or food caches is especially critical for animals
that are year-round residents. Many species have rel-
atively large feet that enable swift travel across deep
snow, for example, red squirrels, martens, lynx, and of
course, snowshoe hares. 13 A few are able to enter a state
of torpor, or reduced physiological activity brought
about by decreased metabolism and body temperature.
examples include bears, marmots, bats, reptiles, and
amphibians. 14
Fig. 11.2. Microphotograph showing swollen mycorrhizal root
tips on lodgepole pine. the filamentous hyphae of the fungus
extend from the bulbous tips into the soil, facilitating the
uptake of water and nutrients. Photo by Steven L. Miller.
When the leaves of evergreen plants are about to fall,
their limiting nutrients are first partially reabsorbed by
the twig. 9 thus, plants in nutrient-deficient environ-
ments have evolved mechanisms for conserving the
limiting nutrients they already have.
Short, cool growing seasons also present problems for
seedling establishment, because plants that are only a few
months old are the most susceptible to water, tempera-
ture, and nutrient stresses. Seeds often germinate despite
cool temperatures in the spring, allowing the maximum
time possible for seedlings to develop the stored energy
and cold-hardened tissues needed for the following win-
ter. Moreover, the formation of mycorrhizal roots typi-
cally occurs in the first few weeks after germination. 10
Despite these adaptations, seedlings often succumb to
summer drought, late-spring frosts, and other factors. 11
Because seedling establishment is so precarious, nearly
all mountain plants are perennials that live for many
years.
Different species have evolved to tolerate differ-
ent levels of environmental stress—a fundamental
principle in considering the causes of patches in land-
scapes anywhere—and stress levels change rapidly
with changes in elevation, soil, and topographic posi-
tion. consequently, species composition often changes
abruptly in the mountains. Variation occurs even with-
out changes in species composition, as many species
have a wide range of genetically determined tolerances.
The Forest Community
Forests are characterized by trees, but, with regard to
the numbers of species, most plants in the commu-
nity are shrubs and herbaceous plants in the under-
story. common shrubs include buffaloberry, dwarf
huckleberry, and ground juniper; the herbs include
heartleaf arnica, lousewort, pyrola, and various grasses
and sedges (table 11.1). Many animals and legions of
microorganisms coexist with the plants. in one way or
another, all are adapted to living with the other spe-
cies, large and small. indeed, some are dependent on
others. A special example consists of plants known  as
mycoheterotrophs —those that lack chlorophyll and
obtain their energy from decaying tree roots by way
of saprophytic fungi. A common example in Rocky
Mountain forests is pinedrops ( Pterospora andromedea ).
clearly, understanding forest ecology is not possible by
studying the trees alone.
 
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