The Forest Ecosystem - Mountains and Plains: The Ecology of Wyoming Landscapes - page 215

differences in nitrogen outflow between thinned
and clearcut stands suggest that the surviving trees
in thinned stands play an important role in nutrient
immobilization. 57
A confounding factor when selecting a silvicultural
system for lodgepole pine forest is whether the manage-
ment goal is to reduce the amount of dwarf mistletoe
(see chapter 11), which, though a native species, is
viewed as a problem for timber production. if that is the
goal, then managers strive to cut all trees infected with
the mistletoe. that seems simple, but the mistletoe is
difficult to see on many trees, which invariably leads to
some infected trees being missed and allowing mistle-
toe to spread to pine seedlings. As noted in the previ-
ous chapter, dwarf mistletoe was probably controlled in
pre-european times by periodic fires. in some places, it
is difficult to use timber harvesting to accomplish the
same objective—except by clearcutting. Another con-
cern with partial cutting of lodgepole pine, engelmann
spruce, and subalpine fir forests is that the residual trees
are sometimes vulnerable to windthrow.
Regardless of whether the forest is subjected to par-
tial or total tree death—whether by burning, cutting, or
insect epidemics—the lost nutrients are a small portion
of the total nutrient capital. the leaching of nutrients is
elevated for perhaps 10 years, possibly more, but the dis-
turbances do not slow nutrient inputs. Most likely the
lost nutrients are replaced in a few decades at the most.
Soil erosion is a more serious concern. Still, with proper
precautions it should be possible to ensure the continu-
ation of soil development and retention. though hav-
ing significant impacts at the time they occur, both
crown fires and clearcuts are infrequent events. A big-
ger concern is the proportion of a watershed or forested
landscape affected during a period of time.

ics become more frequent because of warmer winters,
and will the number of costly fires increase because of
longer fire seasons? What are future forests likely to look
like, and how should the forests be managed to conserve
their biological diversity? Plausible scenarios can be pro-
posed, given what has been learned thus far about forest
ecology, the effects of recent climate change, and the
responses of Rocky Mountain forests to previous epi-
sodes of climate change (see chapter 2).
Warming has been occurring for many years and
is well documented (see chapters 2 and 3). Less well
known is whether precipitation over the mountains
will decline. even if annual precipitation does not
change substantially, warmer temperatures will cause
evapotranspiration to increase, especially in the sum-
mer, leading to more frequent droughts. Also, warmer
winters will cause more precipitation to fall as rain
rather than snow, and a shallow snowpack combined
with warm spring temperatures will lead to earlier
snowmelt, earlier drying of fuels, a longer fire season,
and a longer period for trees to be water stressed. Very
likely, climate change will lead to more frequent insect
outbreaks; more frequent large fires; and reduced water
supplies for towns, industry, and agriculture. Forest
regeneration will sometimes fail if extended droughts
become more common 58 and if more frequent fires
occur. Most forest types may shift upward in eleva-
tion, as the alpine climate becomes favorable for tree
growth—resulting in less total forest cover because
there is less land area at higher elevations. 59 c onsider-
ing the current climate requirements of the prevalent
forest trees today, U.S. Forest Service scientist Gerald
Rehfeldt and his colleagues concluded that, by the end
of the twenty-first century, forests are likely to cover
less area in the western United States than they do
now. 60 today, forests cover only about 15 percent of
Wyoming (see fig. 1.5)
What can be done about the prospect of reduced
water supplies? Knowing that transpiration is reduced
and water outflow enhanced in forests having less leaf
area, as discussed above, some planners have suggested
that water supplies could be augmented by increasing
the harvesting of mountain forests. 61 Although possible,
substantial increases could be produced only from forests
that receive the largest amounts of precipitation, that is,
forests at the highest elevations, and such increases in

The Future of Mountain Forests

Many forests in the region show the imprint of a century
of intensive use, having been fragmented by roads, tim-
ber harvesting, homes, and other developments. others
have been altered only slightly, such as in roadless areas.
everywhere, however, big changes loom because of cli-
mate change. Will warming affect precipitation patterns
in ways that reduce water availability for tree growth
as well as downstream users? Will bark beetle epidem-