��� Forest vegetation is restricted to areas of relatively high precipita~ tion and moderate temperatures. Most of the forests in the San Juan Mountains are dominated by various species of evergreen co~ niferous trees. Evergreens are especially well adapted to environ~ ments with short growing seasons (because of long winters, summer droughts, or both) and scarce soil nutrients. Evergreen trees need not expend a large amount of energy and nutrients in growing a full set of new leaves every year. Evergreen forests are common in the harsh climates of the northeastern and Great Lake states, in Canada, Europe, and Asia, on the infertile soils of the coastal plain in the southeastern United States, and at middle to high elevations throughout the Rocky Mountain Cordillera. Middle~altitude slopes of the San Juan Mountains are cov~
[1]
P. Carrara,et al.
Holocene Treeline Fluctuations in the Northern San Juan Mountains, Colorado, U.S.A., as Indicated by Radiocarbon-Dated Conifer Wood
,
1991
.
[2]
E. C. Pielou,et al.
After the Ice Age : the return of life to glaciated North America
,
1991
.
[3]
W. Baker,et al.
Spruce beetles and fires in the nineteenth-century subalpine forests of western Colorado, USA.
,
1990
.
[4]
E. C. Pielou.
A Repopulation. (Book Reviews: After the Ice Age. The Return of Life to Glaciated North America.)
,
1991
.
[5]
N. Debyle,et al.
Aspen : Ecology and Management in the Western United States
,
1985
.