The Forest Ecosystem - Mountains and Plains: The Ecology of Wyoming Landscapes - page 214

stands are repeatedly harvested at short intervals and if
the slash is burned. 51
With increasing recognition of the ecological
importance of large wood on the forest floor and in the
soil, researchers and managers are exploring ways to
modify clearcutting operations to increase the amount
of wood that remains after harvest. For example, mod-
eling studies suggest that simply doubling the usual
amount of slash and large wood left on a site after
every harvest could bring long-term wood dynam-
ics much closer to the conditions associated with the
natural history of these forests. 52 Piling and burning
this material, with the intent of reducing flammabil-
ity or to reduce habitat for certain insects, may not be
advisable.
it is disconcerting to some observers that forest
fires—a natural phenomenon—might lead to more
erosion and nutrient loss than clearcutting, which is
an artificial, human-caused disturbance. Such adverse
effects must be placed in the context of current con-
ditions. erosion from mountain forests before road
construction and similar kinds of construction was
probably less common than it is today, a time when
all erosion is viewed as a sign of poor management.
However, prior to this modern predicament, the epi-
sodic but infrequent addition of sediments and nutri-
ents to streams could have been beneficial, in terms
of higher stream productivity and possibly higher bio-
logical diversity. Various studies have hypothesized
beneficial effects of erosion and nutrient additions to
aquatic ecosystems after fires, even to the point of sug-
gesting that pulses in aquatic productivity might be
tied to periodic fires that burn a substantial portion
of the watershed. 53 Such benefits are doubtful today
because of the numerous sources of eroded materials
in most landscapes. exceptions are in some large road-
less areas, including those designated Wilderness by
congress.
thus far, clearcutting has been the focus of this dis-
cussion, because it is the most intense kind of human-
caused disturbance and is most comparable with crown
fire, the most intense disturbance that some consider
“natural.” However, less-intense selective harvesting is
often feasible. 54 it is now common to leave numerous
trees standing in what otherwise might be considered a
clearcut. Known as green tree retention, this practice pro-

vides perches for some birds, such as raptors, as well as
a continuous supply of dead standing trees and downed
wood in the future as these trees die and fall. the dead
trees, known as snags, also provide important habitat
for cavity-nesting birds, such as woodpeckers, small
owls, and nuthatches. 55
Selective cutting leaves many trees in place (fig.
12.14) and can mimic the spatial patterns and variable
intensities of insect outbreaks and low-severity fires.56 56
Moderate levels of evapotranspiration are still possible,
and the root systems of the remaining trees continue
to take up nutrients and minimize erosion. one study
in a lodgepole pine forest estimated that removing
about half the total leaf area resulted in nearly dou-
bling the amount of water outflow, yet the outflow of
nitrogen remained low. in contrast, clearcutting led
to a nearly threefold increase in water outflow and a
sixfold increase in total nitrogen outflow. the marked

Fig. 12.14. Selective harvesting, or thinning, preserves much
of the forest structure in this ponderosa pine forest in the
Black Hills. comparable results may not be achieved in other
kinds of forests.