Alternative site for the Global ecosystem typology with additional information for ecosystem profiles and indicative maps.
This site is maintained by jrfep
Ecological functions within the Savannas and grasslands biome are closely linked to a continuous groundlayer of grasses that contribute moderate to very high levels of primary productivity driven by strongly seasonal water surplus/deficit cycles. The timing of the seasonal cycle of productivity varies with latitude and becomes more variable interannually as total rainfall declines. The woody component of vegetation may be completely absent or varies to a height and stature that resembles forest. In the tropics and subtropics productivity peaks in summer when high rainfall coincides with warm temperatures. At temperate latitudes, summer growth is suppressed by water deficits associated with high evapotranspiration, sometimes exacerbated by weakly seasonal (winter-maximum) rainfall, so that productivity typically peaks in spring when warming temperatures coincide with high soil moisture accumulated over winter. Co-existence between trees and grasses, and between grasses and interstitial forbs, is mediated by herbivory and/or fire. These agents are critical in top-down regulation of grassy ecosystems and in some cases, are involved in feedback mechanisms that mediate regime shifts between alternative stable states. Herbivory is the primary driver in highly fertile and productive systems whereas fire is the primary driver in less fertile and lower productivity systems. Nutrient gradients are thus exacerbated by the loss of nutrient through volatilisation. The representation of grass species with C3 and C4 photosynthetic pathways varies with water availability and temperature over regional and continental climatic gradients. Grasses are rapid responders to seasonal pulses of elevated soil moisture and sustain a complex trophic web, with large-bodied mammalian herbivores and their predators. The curing of grasses over the dry season is critical to flammability. Mammal diversity, trophic complexity and the expression of physical and chemical defences against herbivory also vary with soil fertility.