More rain leads to fewer trees in the African savanna

In 2011, satellite images of the African savannas revealed a mystery: these rolling grasslands, with their heavy rainfalls and spells of drought, were home to significantly fewer trees than researchers had expected. Scientists supposed that the ecosystem's high annual precipitation would result in greater tree growth. Yet a 2011 study found that the more instances of heavy rainfall a savanna received, the fewer trees it had.

The researchers found that under very wet conditions, grasses have an advantage because they can quickly absorb water and support high rates of photosynthesis, the process by which plants convert sunlight into energy. Trees, with their tougher leaves and roots, are able to survive better in dry periods because of their ability to withstand water stress. But this amounts to a disadvantage for trees in periods of intense rainfall, as they are comparatively less effective at utilizing the newly abundant water.

The study highlights the importance of understanding the pattern and intensity of rainfall, not just the total annual precipitation, which is where most research in this area has focused, Xu said. In 50 years, a region may still experience the same overall amount of precipitation. If the intensity changes, however, that will affect the abundance of grasses and trees. This, in turn, will influence the herbivores that subsist on them, and other animals in the biome -- essentially, affecting the entire ecosystem.

Citation:

Princeton University. "More rain leads to fewer trees in the African savanna." ScienceDaily. ScienceDaily, 19 October 2015. <www.sciencedaily.com/releases/2015/10/151019130802.htm>.