Environmental Engineering Reference
In-Depth Information
them very efficient photosynthesizers where light conditions are strong, as in savanna
regions. However, there is some evidence that their ecological advantage may be less
strong in an atmosphere of higher carbon dioxide concentration. With C
3
plants, the
elevated carbon dioxide levels of the enhanced greenhouse effect atmosphere are
expected to lead to greater plant growth, but this is unlikely to occur with the C
4
group,
where solar radiation is more important. Species of the C
4
type include major food crops
such as maize and sugar cane which, unlike the temperate cereal crops and rice, would
not be expected to benefit from increased levels of carbon dioxide.
modifiers of the primary factors of moisture and nutrient supply, though human
influences become significant here as they can affect the intensity of both fire and grazing
intensity. Studies in South African savanna have demonstrated a relationship between
Iron Age settlements and species dominance. Where nutrients have been added as a result
of activities within the settlement, such as through burning and waste,
Acacia
species can
be supported, but without any additional nutrients the nutrient-poor
Burkea africana
savanna dominated.
SAVANNA SOILS
The soils of the savanna are variable. They include ferralsols, acrisols, vertisols and
luvisols. Their distribution is related to climatic, geological and geomorphological
conditions. Slope processes are active, for the vegetation is often insufficient to prevent
erosion and downwashing of nutrients. Consequently, marked catena sequences develop
on the hill slopes, grading from shallow stony soils to deeper, less well drained, base-rich
alluvial soils (Figure 27.5). The ridge crests (or 'breakaways') are usually formed of
hardened iron oxides (laterite) and indicate old erosion surfaces.
WILDLIFE
The number of animal species is relatively low in the savannas, though their populations
are large. Surprisingly, interspecific competition seems to be limited, and the food chains
are short, with few secondary consumers. Most carnivores prey directly on herbivores.
For example, lions attack mainly zebra, wildebeest, antelope and giraffe. However, many
scavengers and decomposers, including mammals and insects, also feed on the lions'
kills. Termites
