Slide 8: Controls on grass growth at the annual timescale
These are the main factors known to control how much grass grows every year. First of these is the rainfall, although it is not so much the quantity of rain that matters, as the duration of growth opportunity (ie: that length of time in which conditions are appropriate for growth). This factor is affected by evaporation as well as rain, and the effects of soil texture on the drainage of water from the soils plays an important role. The soil fertility is important, and the tree cover plays a role because grass typically does not grow well under shade. Daytime temperatures must fall within an optimal range for grass growth, and, as shown in Chapter 4, the levels of CO2 in the air can be a significant factor in controlling plant growth.
In some fertile savanna ecosystems, moderate grazing also has a mildly stimulating effect on grass growth.