TY  - JOUR
A1  - Synodinos, Alexis D.
A1  - Tietjen, Britta
A1  - Lohmann, Dirk
A1  - Jeltsch, Florian
T1  - The impact of inter-annual rainfall variability on African savannas changes with mean rainfall
JF  - Journal of theoretical biology
N2  - Savannas are mixed tree-grass ecosystems whose dynamics are predominantly regulated by resource competition and the temporal variability in climatic and environmental factors such as rainfall and fire. Hence, increasing inter-annual rainfall variability due to climate change could have a significant impact on savannas. To investigate this, we used an ecohydrological model of stochastic differential equations and simulated African savanna dynamics along a gradient of mean annual rainfall (520–780 mm/year) for a range of inter-annual rainfall variabilities. Our simulations produced alternative states of grassland and savanna across the mean rainfall gradient. Increasing inter-annual variability had a negative effect on the savanna state under dry conditions (520 mm/year), and a positive effect under moister conditions (580–780 mm/year). The former resulted from the net negative effect of dry and wet extremes on trees. In semi-arid conditions (520 mm/year), dry extremes caused a loss of tree cover, which could not be recovered during wet extremes because of strong resource competition and the increased frequency of fires. At high mean rainfall (780 mm/year), increased variability enhanced savanna resilience. Here, resources were no longer limiting and the slow tree dynamics buffered against variability by maintaining a stable population during ‘dry’ extremes, providing the basis for growth during wet extremes. Simultaneously, high rainfall years had a weak marginal benefit on grass cover due to density-regulation and grazing. Our results suggest that the effects of the slow tree and fast grass dynamics on tree-grass interactions will become a major determinant of the savanna vegetation composition with increasing rainfall variability.
KW  - Rainfall variability
KW  - Savanna-grassland bistability
KW  - Stochastic differential equations
KW  - Coexistence mechanisms
KW  - Fire
Y1  - 2017
U6  - https://doi.org/10.1016/j.jtbi.2017.10.019
SN  - 0022-5193
SN  - 1095-8541
VL  - 437
SP  - 92
EP  - 100
PB  - Elsevier Ltd.
CY  - London
ER  -