Slide 15: Effect of CO2 on NEP
Rising levels of carbon dioxide in the atmosphere have a stimulatory effect on plant growth. This effect saturates above about 1000 parts per million (ppm), and is different for C4 photosynthetic plants (tropical grasses) and C3 plants (trees). A simple 'phenomenological' model that fits the empirical data uses a 'beta function'. [A phenomenological model is one that does not try to explain the underlying process, it just reproduces the result]
Hence, in conditions of increasing carbon dioxide, as currently is occurring through anthropogenic causes, it is likely that the proportion of trees in the savanna ecosystem will increase.