Geography Reference
In-Depth Information
versity (Agee 1993). Fire exclusion has thus led to a dramatic reduction of habitat di-
versity and species richness for both plants and animals (e.g., Noss et al. 2006).
Lower fire frequencies combined with greater fire severities may also have long-term
effects on forest stability by promoting certain life-history characteristics of fire-adap-
ted tree species (e.g., Kauffman 1990). This is especially notable in areas where aspen
stands contribute a large portion of the plant species diversity in subalpine and mont-
ane forests. Aspen ( Populus tremuloides ) is a broadly distributed pioneer species that is
becoming less dominant in western North American forests as the result of fire suppres-
sion and its replacement by more shade-tolerant species, such as subalpine fir ( Abies
lasiocarpa ) and Engelmann spruce ( Picea engelmannii ) (e.g., Peet 2000).
Mountain meadows are important components of many forest landscapes and are of-
ten related to forest succession and disturbance. The origin of meadows can be the res-
ult of environmental factors including poor drainage, shallow soils, low soil nutrients,
snowpack, or disturbance (e.g., Jakubos and Romme 1993; Miller and Halpren 1998).
Research on physical and biological processes, such as climate variability, fire occur-
rence, and fire exclusion (Taylor 1990; Rochefort and Peterson 1996; Hadley 1999),
grazing (Miller and Halpren 1998), and competition among plants (e.g., Magee and An-
tos 1992), reveals that many mountain meadows in the western United States have ex-
perienced high rates of recent tree establishment and meadow closure (e.g., 0.1 to 0.5
m/year or 0.3-1.6 ft/year; Hadley and Savage 1996), resulting from episodes of favor-
able climate conditions for seedling establishment in conjunction with changes in man-
agement strategies around fire suppression and grazing allotments (e.g., Belsky and
Blumenthal 1997).
Similar to the issue of declining aspen in the Rocky Mountains, resource managers
are confronted with two difficult choices regarding the sustained presence of mountain
meadows: (1) refraining from intervention that might allow tree encroachment to con-
tinue and decrease the size or eliminate many meadows; or (2) attempt to preserve
meadows through active management, such as prescribed burning or clearing young
trees and saplings (e.g., Franklin et al. 1971). Little is known about how active manage-
ment might influence these meadows; in some cases, these strategies could increase the
rate of seedling establishment by removing herbaceous plants that compete and inhibit
seedling establishment (cf. Magee and Antos 1992).
In contrast to the predominantly natural meadows of western North America, moun-
tain meadows in Europe are generally the result of human activity. These meadows are
common landscape features of the Alps, Carpathians, and Caucasus, exhibiting high
species richness, with as many as 60 species occurring in areas as small as 25 m 2 (269
ft 2 ). Initially maintained by hay harvests, many of these visually attractive meadows are
now abandoned or preserved as “cultural treasures” financed by external funds. Nat-
ural mountain meadows below timberline are generally restricted to active avalanche
paths.
Timberline
The transition between the subalpine forest and alpine tundra vegetation identifies the
location of the alpine ecotone. Ecotones indicate changes in ecological conditions where
differences in plant stature and form ( physiognomy ) become important adaptations to
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