Effects of Fire and Herbivory on the Stability of Savanna Ecosystems

Savanna ecosystems are characterized by the co-occurrence of trees and grasses. In this paper, we argue that the balance between trees and grasses is, to a large extent, determined by the indirect interactive effects of herbivory and fire. These effects are based on the positive feedback between fue...

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Bibliographic Details
Published in:Ecology (Durham) 2003-02, Vol.84 (2), p.337-350
Main Authors: van Langevelde, Frank, Claudius A. D. M. van de Vijver, Kumar, Lalit, van de Koppel, Johan, de Ridder, Nico, van Andel, Jelte, Skidmore, Andrew K., Hearne, John W., Stroosnijder, Leo, Bond, William J., Herbert H. T. Prins, Rietkerk, Max
Format: Article
Language:English
Subjects:
african savanna
alternate stable states
Animal behavior
Biological and medical sciences
Biomass
Browsing
bush encroachment
catastrophe
coexistence
dynamics
ecology
Ecosystems
fire
Fire Ecology
Fires
Flowers & plants
Forest and land fires
Fundamental and applied biological sciences. Psychology
Grasses
grazing
herbivory
management
Phytopathology. Animal pests. Plant and forest protection
positive feedback
Rhizosphere
savanna
Savannas
semiarid grazing systems
simulation-model
Soil water
Soil water content
stability
Trees
tree–grass balance
Vegetation
Weather damages. Fires
Woodlands
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Summary:Savanna ecosystems are characterized by the co-occurrence of trees and grasses. In this paper, we argue that the balance between trees and grasses is, to a large extent, determined by the indirect interactive effects of herbivory and fire. These effects are based on the positive feedback between fuel load (grass biomass) and fire intensity. An increase in the level of grazing leads to reduced fuel load, which makes fire less intense and, thus, less damaging to trees and, consequently, results in an increase in woody vegetation. The system then switches from a state with trees and grasses to a state with solely trees. Similarly, browsers may enhance the effect of fire on trees because they reduce woody biomass, thus indirectly stimulating grass growth. This consequent increase in fuel load results in more intense fire and increased decline of biomass. The system then switches from a state with solely trees to a state with trees and grasses. We maintain that the interaction between fire and herbivory provides a mechanistic explanation for observed discontinuous changes in woody and grass biomass. This is an alternative for the soil degradation mechanism, in which there is a positive feedback between the amount of grass biomass and the amount of water that infiltrates into the soil. The soil degradation mechanism predicts no discontinuous changes, such as bush encroachment, on sandy soils. Such changes, however, are frequently observed. Therefore, the interactive effects of fire and herbivory provide a more plausible explanation for the occurrence of discontinuous changes in savanna ecosystems.
ISSN:0012-9658
1939-9170
DOI:10.1890/0012-9658(2003)084[0337:EOFAHO]2.0.CO;2