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Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

Published online by Cambridge University Press:  11 October 2010

Lynda D. Prior*
Affiliation:
School for Environmental Research, Charles Darwin University, Darwin, Northern Territory 0909, Australia School of Plant Science, University of Tasmania, Hobart, Tasmania 7001, Australia
Richard J. Williams
Affiliation:
CSIRO Sustainable Ecosystems, PMB 44, Winnellie, Northern Territory 0822, Australia
David M. J. S. Bowman
Affiliation:
School of Plant Science, University of Tasmania, Hobart, Tasmania 7001, Australia
*
1Corresponding author. Email: lynda.prior@utas.edu.au

Abstract:

A fire-mediated recruitment bottleneck provides a possible explanation for the coexistence of trees and grasses in mesic savannas. The key element of this hypothesis is that saplings are particularly vulnerable to fire because they are small enough to be top-killed by grass fires, but unlike juveniles, they take several years to recover their original size. This limits the number of recruits into the adult size classes. Thus savanna vegetation may be maintained by a feedback whereby fire restricts the density of adult trees and allows a grass layer to develop, which provides fuel for subsequent fires. Here, we use results from a landscape-scale fire experiment in tropical Australia, to explore the possible existence of a recruitment bottleneck. This experiment compared tree recruitment and survival over 4 y under regimes of no fire, annual early and annual late dry-season fire. Stem mortality decreased with increasing stem height in the fire treatments but not in the unburnt treatment. Tree recruitment was 76–84% lower in the fire treatments than the unburnt treatment. Such fire-induced stem loss of saplings and reduced recruitment to the canopy layer in this eucalypt savanna are consistent with the predictions of the fire-mediated recruitment bottleneck hypothesis.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2010

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