Fire controls population structure in four dominant tree species in a tropical savanna |
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Authors: | Caroline E R Lehmann Lynda D Prior David M J S Bowman |
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Institution: | (1) School for Environmental Research, Institute for Advanced Studies, Charles Darwin University, Darwin, NT, 0909, Australia;(2) School of Plant Science, University of Tasmania, Hobart, TAS, 7001, Australia |
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Abstract: | The persistence of mesic savannas has been theorised as being dependent on disturbances that restrict the number of juveniles
growing through the sapling size class to become fire-tolerant trees. We analysed the population structures of four dominant
tropical savanna tree species from 30 locations in Kakadu National Park (KNP), northern Australia. We found that across KNP
as a whole, the population size structures of these species do not exhibit recruitment bottlenecks. However, individual stands
had multimodal size-class distributions and mixtures of tree species consistent with episodic and individualistic recruitment
of co-occurring tree species. Using information theory and multimodel inference, we examined the relative importance of fire
frequency, stand basal area and elevation difference between a site and permanent water in explaining variations in the proportion
of sapling to adult stems in four dominant tree species. This showed that the proportion of the tree population made up of
saplings was negatively related to both fire frequencies and stand basal area. Overall, fire frequency has density-dependent
effects in the regulation of the transition of saplings to trees in this Australian savanna, due to interactions with stem
size, regeneration strategies, growth rates and tree–tree competition. Although stable at the regional scale, the spatiotemporal
variability of fire can result in structural and floristic diversity of savanna tree populations. |
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Keywords: | Demography Fire Population dynamics Tree– grass coexistence Tree– tree competition |
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