Mountain Vegetation - Mountain Geography: Physical and Human Dimensions - page 336

Many of the characteristics of mountain plant communities change with increasing el-
evation, including a decrease in species richness and changes in plant stature, form,
and structure ( physiognomy ) . The most obvious visual change in mountain plants is the
tendency toward smaller stature and less elaborate plants with increasing elevation.
Other characteristics of high-elevation plants include lower annual growth rates and
lower annual productivity. Exceptions to these general trends occur in some tropical
cloud forests and desert mountains, where diversity and plant size increase along with
increases in precipitation (Myers 1969; Pearson and Ralph 1978).
Mountain Forests
Mountain forests are generally categorized according to their zonal elevational distri-
butions. Lower mountain forests within an elevational sequence are referred to as the
submontane or montane zones, which are often divided into upper and lower areas.
Higher-elevation forests comprise the subalpine zone, below the high-elevation, treeless
alpine zone (Fig. 7.1). Zonal patterns in equatorial and tropical mountains diverge from
this general trend in response to strong regional influences exerted by the Intertropic-
al Convergence Zone (ITCZ), smaller continental landmasses, and monsoon conditions.
Consequently, the number and distribution of elevational zones in tropical high moun-
tains are far more complex than at higher latitudes. This calls for additional clarification
and standardization of zonal nomenclature to improve comparisons of vegetation zones
at different latitudes (e.g., Fickert and Richter 2004).
The trees of mountain forests are most easily categorized according to three distinct
leaf growth forms ( habits ): needle-leaf conifers; broadleaf evergreen trees; and
broadleaf deciduous trees. Needle-leaf conifers dominate most of the mid- to high-latit-
ude regions of the northern hemisphere. Conifers are important montane forest trees in
the southern hemisphere, but are generally subdominant to broadleaf evergreen trees.
These once broadly distributed southern hemisphere conifers represent different gen-
era with life forms (e.g., araucaria “pine” or monkey-puzzle tree [ Araucaria spp.]) that
are distinctly different from those that are dominant in the northern hemisphere, and
are now most concentrated in wet environments (Hill and Brodribb 1999). Broadleaf
evergreen trees tend to dominate in warm, humid regions with small temperature
ranges, including both the tropics and the marine-influenced midlatitude regions of the
southern hemisphere. In the northern hemisphere, deciduous broadleaf trees dominate
midlatitude forests in humid continental climates with sharp seasonal contrasts associ-
ated with subcontinental-scale atmospheric circulation patterns (Delcourt and Delcourt
2000).
Northern Hemisphere Mountain Forests
NORTHERN HEMISPHERE CONIFER FORESTS
Evergreen conifers dominate most higher-elevation forests in the northern hemisphere;
they include several species closely related to those found in the boreal forests of North
America and Eurasia. This similarity suggests a common ancestry for these forests and
helps to explain the dominance of three tree genera, pine ( Pinus spp.), spruce ( Picea