The Mountain Ecoregions
9
9.1
M Mountains with Elevational
Zonation
Highland systems are characterized by change
more than any other regional system. On the geologic time scale they are subject to rapid changes
in topography. Highland areas are associated with
the margins of crustal plates, and the great
elevations result from the upwarping of the crust
along the plate boundaries and the upwelling of
magma that forms the volcanic peaks and massive
lava flows. These are the zones where volcanic
activity is common and where earthquakes may
be expected. The high relief, steep slopes, and
generally higher precipitation accelerate erosional
processes. Mass wasting is a widespread phenomenon in highlands, including avalanches and
landslides (Fig. 9.1). It is these relatively high
rates of geologic modification by both internal
and external forces which give the highlands
their rugged aspect.
Mountain
climates
are
vertically
differentiated, based on the effects of change in
elevation. Air cools while ascending a mountain
slope, and its capacity to hold water decreases,
causing an increase in rain and snow. The thin,
dry air loses heat rapidly as it ascends, and after
sunset, temperatures plummet.
Elevations show typical climatic characteristics,
depending on a mountain range’s location in the
overall pattern of global climatic zones. The climate of a given highland area is usually closely
related to the climate of the surrounding lowland in
seasonal character, particularly the form of the
annual temperature cycle, and the times of occurrence of wet and dry seasons. For example, the
Ethiopian Plateau is subject to a diurnal energy
pattern, a nonseasonal energy pattern, and a seasonal moisture regime consists of a rainy summer
and a dry winter (Fig. 9.2).
Since high mountains extend vertically
through several climatic zones, their vegetation
is usually rather sharply marked into zones. The
elevational limits of various types of vegetation
also correspond to the pattern of vertical temperature distribution. Roughly, the same succession
of types is found in ascending mountains near
the equator as it is found proceeding poleward
along the continental east coasts. As discussed in
Chap. 4, each mountain within a zone has a
typical sequence or spectra of altitudinal belts
(Table 9.1). For example, in the tropical
rainforest, the tropical forest occupies the lower
slopes, higher up are the mixed montane forests
of broadleaf types with epiphytes (Fig. 9.3), and
beyond the upper limit of trees but below the
snow line, is a zone of alpine meadows. Conifers
do not appear at higher elevations south of
Nicaragua.
As far as vegetation and other forms of life are
concerned, the vertical differentiation reaches a
maximum in the low latitudes. Here we find the
greatest variety of zones. Vertical differentiation
remains a conspicuous feature of mountains in
the middle latitudes, but disappears altogether in
the high latitudes. The effect of latitude was first
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9_9, # Springer Science+Media, LLC 2014
89
9
9.1
M Mountains with Elevational
Zonation
Highland systems are characterized by change
more than any other regional system. On the geologic time scale they are subject to rapid changes
in topography. Highland areas are associated with
the margins of crustal plates, and the great
elevations result from the upwarping of the crust
along the plate boundaries and the upwelling of
magma that forms the volcanic peaks and massive
lava flows. These are the zones where volcanic
activity is common and where earthquakes may
be expected. The high relief, steep slopes, and
generally higher precipitation accelerate erosional
processes. Mass wasting is a widespread phenomenon in highlands, including avalanches and
landslides (Fig. 9.1). It is these relatively high
rates of geologic modification by both internal
and external forces which give the highlands
their rugged aspect.
Mountain
climates
are
vertically
differentiated, based on the effects of change in
elevation. Air cools while ascending a mountain
slope, and its capacity to hold water decreases,
causing an increase in rain and snow. The thin,
dry air loses heat rapidly as it ascends, and after
sunset, temperatures plummet.
Elevations show typical climatic characteristics,
depending on a mountain range’s location in the
overall pattern of global climatic zones. The climate of a given highland area is usually closely
related to the climate of the surrounding lowland in
seasonal character, particularly the form of the
annual temperature cycle, and the times of occurrence of wet and dry seasons. For example, the
Ethiopian Plateau is subject to a diurnal energy
pattern, a nonseasonal energy pattern, and a seasonal moisture regime consists of a rainy summer
and a dry winter (Fig. 9.2).
Since high mountains extend vertically
through several climatic zones, their vegetation
is usually rather sharply marked into zones. The
elevational limits of various types of vegetation
also correspond to the pattern of vertical temperature distribution. Roughly, the same succession
of types is found in ascending mountains near
the equator as it is found proceeding poleward
along the continental east coasts. As discussed in
Chap. 4, each mountain within a zone has a
typical sequence or spectra of altitudinal belts
(Table 9.1). For example, in the tropical
rainforest, the tropical forest occupies the lower
slopes, higher up are the mixed montane forests
of broadleaf types with epiphytes (Fig. 9.3), and
beyond the upper limit of trees but below the
snow line, is a zone of alpine meadows. Conifers
do not appear at higher elevations south of
Nicaragua.
As far as vegetation and other forms of life are
concerned, the vertical differentiation reaches a
maximum in the low latitudes. Here we find the
greatest variety of zones. Vertical differentiation
remains a conspicuous feature of mountains in
the middle latitudes, but disappears altogether in
the high latitudes. The effect of latitude was first
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9_9, # Springer Science+Media, LLC 2014
89