(Fig. 4.7). They are arranged in a regular,
repeated pattern with reference to latitude and
position on the continents.
Within each of these zones, one or several
climatic gradients may affect the potential distribution of the dominant vegetation. Within the
humid tropical zone, for example, we can distinguish rainforests that have year-round precipitation from savannas that receive seasonal
precipitation. Thus, we can subdivide the humid
tropical zone, based on moisture distribution
(Fig. 4.8) into climatic subzones. We can subdivide the other zones similarly.
Locating the boundaries of broad-scale
ecosystems requires taking into account visible
and tangible expressions of climate such as
vegetation. Generally, each climate is associated
with a single plant formation class (such as
savanna, see Fig. 8.5, p. 84, Table 4.1), and is
characterized by a broad uniformity both in
appearance and in composition of the dominant
plant species. Usually a significant correspondence with soils occurs because climate also
strongly dominates soil-forming processes.
Of course, not all the area is taken up by the
formation, because the nature of the topography
will allow the differentiation into many sites.
One ignores these local variations in mapping
climatic regions (and therefore ecoregions).
The vegetation conditions indicated by plant
formation name refer to undisturbed plant cover
that is known to exist or is assumed to grow if
Fig. 4.2 Variation in air
temperature through the
day and through the year in
tropical, temperate, and
polar zones. Stations are
Singapore, Oxford,
England, and McMurdo
Sound, Antarctica,
respectively. From Troll
(1966), p. 15–16
4.1 The Controls of Macroclimate
29
repeated pattern with reference to latitude and
position on the continents.
Within each of these zones, one or several
climatic gradients may affect the potential distribution of the dominant vegetation. Within the
humid tropical zone, for example, we can distinguish rainforests that have year-round precipitation from savannas that receive seasonal
precipitation. Thus, we can subdivide the humid
tropical zone, based on moisture distribution
(Fig. 4.8) into climatic subzones. We can subdivide the other zones similarly.
Locating the boundaries of broad-scale
ecosystems requires taking into account visible
and tangible expressions of climate such as
vegetation. Generally, each climate is associated
with a single plant formation class (such as
savanna, see Fig. 8.5, p. 84, Table 4.1), and is
characterized by a broad uniformity both in
appearance and in composition of the dominant
plant species. Usually a significant correspondence with soils occurs because climate also
strongly dominates soil-forming processes.
Of course, not all the area is taken up by the
formation, because the nature of the topography
will allow the differentiation into many sites.
One ignores these local variations in mapping
climatic regions (and therefore ecoregions).
The vegetation conditions indicated by plant
formation name refer to undisturbed plant cover
that is known to exist or is assumed to grow if
Fig. 4.2 Variation in air
temperature through the
day and through the year in
tropical, temperate, and
polar zones. Stations are
Singapore, Oxford,
England, and McMurdo
Sound, Antarctica,
respectively. From Troll
(1966), p. 15–16
4.1 The Controls of Macroclimate
29