25 April 2019

African savannas affected by how often and how hard it rains during the wet-season

Photo: D. D' Onofrio

Climate change is expected to increase rainfall across Africa. But how will this affect savannas and grasslands? A new publication in Scientific Reports (Nature Springer) has established how intensity and frequency of rainfall influences the balance between trees and grasses in savannas and grasslands, and provides insights in how we can manage such areas under a changing climate.

Grasslands and savannas cover about a third of Africa and a fifth of the world’s land area. They support a growing proportion of the world’s population, are home to the majority of the world’s remaining megafauna, and are a critical store of biodiversity. Despite their importance, in comparison to tropical forests savannas and grasslands garner little public attention or conservation efforts.

Key role of grass in characterising savannas and grasslands

Recent research co-authored by Copernicus Institute researcher Mara Baudena in collaboration with colleagues from the Italian Research Council CNR in Torino has underlined the key role of grass in characterising savannas and grasslands in sub-Saharan Africa (D’Onofrio et al 2018). However, in general the ability to predict relative dominance of trees and grasses in these biomes remains limited.

D'Onofrio et al. (2019)

Frequency and intensity of rainfall influences balance between trees and grasses

Through analysing satellite data, brand new work co-authored by Mara Baudena and former MSc student Luke Sweeney has been able to establish that both the frequency and intensity of rainfall influences the balance between trees and grasses in savannas and grasslands. In the driest areas, grasses appear to profit from more frequent rainfall. But when you look at wetter areas this completely changes, with more frequent rain instead favouring trees.

Climate change to have contrasting effects

Climate change is expected to increase rainfall intensity across Africa. “These results suggest that this increase in intensity will have contrasting effects,” say Baudena and Sweeney. Grass coverage will decrease in dry savannas, increasing coverage of shrubs and trees in previously open grasslands and rangelands - enhancing a phenomena increasingly observed today. Conversely, in wetter savannas, climate change may limit tree growth. “Understanding these effects will help with the management of these areas especially under the increasing pressure placed on them due to climate change”.

References

D'Onofrio, D., von Hardenberg, J. & Baudena, M.(2018). Not only trees - Grasses determine African tropical biome distributions via water limitation and fire. Global Ecology and Biogeography, 27 (6), (714-725). https://doi.org/10.1111/geb.12735

D'Onofrio, D., Sweeney, L., von Hardenberg, J. & Baudena, M. (2019). Grass and tree cover responses to intra-seasonal rainfall variability vary along a rainfall gradient in African tropical grassy biomes. Scientific Reports, 9 (10 p.). https://doi.org/10.1038/s41598-019-38933-9

Assistant Professor