International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire
RESEARCH ARTICLE

The effect of fire on tree–grass coexistence in savannas: a simulation study

Veiko Lehsten A G , Almut Arneth B , Allan Spessa C D , Kirsten Thonicke E and Aristides Moustakas F

A Department of Physical Geography and Ecosystem Science, Lund University, Sölvegatan 12, SE-223 62 Lund, Almut Arneth, Sweden.

B Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research (IMK-IFU), Kreuzeckbahnstraße 19, 82467 Garmisch-Partenkirchen, Germany.

C Department Environment, Earth and Ecosystems, Faculty of Science, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK.

D Department of Atmospheric Chemistry, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany.

E Potsdam Institute for Climate Impact Research (PIK) e.V., Telegrafenberg, 14473 Potsdam, Germany.

F School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.

G Corresponding author. Email: veiko.lehsten@nateko.lu.se

International Journal of Wildland Fire 25(2) 137-146 http://dx.doi.org/10.1071/WF14205
Submitted: 15 November 2014  Accepted: 26 August 2015   Published: 15 December 2015

Abstract

The savanna biome has the greatest burned area globally. Whereas the global distribution of most biomes can be predicted successfully from climatic variables, this is not so for savannas. Attempts to dynamically model the distribution of savannas, including a realistically varying tree : grass ratio are fraught with difficulties. In a simulation study using the dynamic vegetation model LPJ-GUESS we investigate the effect of fire on the tree : grass ratios as well as the biome distribution on the African continent. We performed simulations at three spatial scales: locally, at four sites inside Kruger National Park (South Africa); regionally, along a precipitation gradient; and for the African continent. We evaluated the model using results of a fire experiment and found that the model underestimates the effect of fire on tree cover slightly. On a regional scale, high frequencies were able to prevent trees from outcompeting grasses in mesic regions between ~700 and 900 mm mean annual precipitation. Across the African continent, incorporation of fire improved notably the simulated distribution of the savanna biome. Our model results confirm the role of fire in determining savanna distributions, a notion that has been challenged by competing theories of tree–grass coexistence.

Additional keywords: African biome distribution, demographic bottleneck hypothesis, dynamic vegetation models, LPJ-GUESS, tree : grass ratio, wildfires.


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