Mountain Forests - Mountains and Plains: The Ecology of Wyoming Landscapes - page 188

Fig. 11.10. Douglas-fir forest
near Jenny Lake in Grand
teton national Park. eleva-
tion 6,850 feet.

establishment of new ponderosa pine seedlings tends to
be episodic, occurring primarily during periods of rela-
tively wet conditions, with or without fire.60 60 As a result,
a ponderosa pine forest often contains only three or
four easily identified age classes.
the earliest explorers surely saw a great diversity of
ponderosa pine forests as they traveled westward. How-
ever, a combination of fire exclusion and heavy grazing,
which enhances tree seedling establishment by reduc-
ing competition from grasses and forbs, caused tree
density in many stands to increase during the twenti-
eth century, especially on drier sites at low elevations
(see fig. 11.8). Wetter conditions also promoted seedling
establishment and survival in areas that were logged in
the early 1900s, when tree removal favored the growth
of young trees in many place s. 61 A ll these factors favored
the development of more extensive and uniform wood-
lands than had occurred historically. Recent large fires,
bark beetle outbreaks, and drought-caused tree mor-
tality, as well as innovative new timber harvesting
methods, may be restoring some of the diversity that
characterized historical ponderosa pine forests. nota-
bly, since about 2000, extensive mountain pine beetle
outbreaks have affected ponderosa pine forests in the

Laramie Mountains near casper and near Laramie Peak
west of Wheatland, and a large fire of variable fire sever-
ity burned near Laramie Peak in the summer of 2012.
the same is true elsewhere in the region.

Douglas-fir Forest

Douglas-fir and ponderosa pine share several ecological
characteristics and sometimes they are found together.
Specifically, both species have a thick bark that often
enables the trees to survive low-intensity surface fires.
Also, the optimal environment for both is at lower eleva-
tions, in the foothills and lower mountain slopes below
about 8,500 feet (see fig. 11.1). Usually Douglas-fir for-
ests are found at slightly higher elevations than pon-
derosa pine, or on somewhat wetter sites; for example,
north-facing slopes often support relatively pure stands
of Douglas-fir, whereas on the opposite, south-facing
slopes, stands may be dominated primarily by ponderosa
pine. Limestone and other sedimentary substrata appear
to be especially favorable for Douglas-fir.62 62 S ome research
suggests that Douglas-fir is more tolerant of competition
for water, nutrients, and light in the understory than is
the pine, and that it can eventually replace the pine in