The impact of inter-annual rainfall variability on African savannas changes with mean rainfall
- 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 wetSavannas 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.…
Author details: | Alexis D. SynodinosORCiD, Britta TietjenORCiD, Dirk LohmannORCiDGND, Florian JeltschORCiDGND |
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DOI: | https://doi.org/10.1016/j.jtbi.2017.10.019 |
ISSN: | 0022-5193 |
ISSN: | 1095-8541 |
Pubmed ID: | https://pubmed.ncbi.nlm.nih.gov/29054812 |
Title of parent work (English): | Journal of theoretical biology |
Publisher: | Elsevier Ltd. |
Place of publishing: | London |
Publication type: | Article |
Language: | English |
Date of first publication: | 2017/10/18 |
Publication year: | 2018 |
Release date: | 2022/02/11 |
Tag: | Coexistence mechanisms; Fire; Rainfall variability; Savanna-grassland bistability; Stochastic differential equations |
Volume: | 437 |
Number of pages: | 9 |
First page: | 92 |
Last Page: | 100 |
Funding institution: | German Research Foundation (DFG)German Research Foundation (DFG) [GRK 1364]; German Federal Ministry of Education and Research (Bundesministerium fur Bildung und Forschung)Federal Ministry of Education & Research (BMBF) [01LL1302A, 01LL1302B] |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Biochemie und Biologie |
DDC classification: | 5 Naturwissenschaften und Mathematik / 57 Biowissenschaften; Biologie / 570 Biowissenschaften; Biologie |
Peer review: | Referiert |