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On the detection of dynamic responses in a drought-perturbed tropical rainforest in Borneo

Lingenfelder, M. ; Newbery, D.

In: Plant Ecology, 2009, vol. 201, no. 1, p. 267-290

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    Title
    • On the detection of dynamic responses in a drought-perturbed tropical rainforest in Borneo
    Author
    • Lingenfelder, M.. Vegetation Ecology Section, Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013, Bern, Switzerland
    • Newbery, D.. Vegetation Ecology Section, Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013, Bern, Switzerland
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:321031
    Summary
    The dynamics of aseasonal lowland dipterocarp forest in Borneo is influenced by perturbation from droughts. These events might be increasing in frequency and intensity in the future. This paper describes drought-affected dynamics between 1986 and 2001 in Sabah, Malaysia, and considers how it is possible, reliably and accurately, to measure both coarse- and fine-scale responses of the forest. Some fundamental concerns about methodology and data analysis emerge. In two plots forming 8ha, mortality, recruitment, and stem growth rates of trees ≥10cm gbh (girth at breast height) were measured in a ‘pre-drought' period (1986-1996), and in a period (1996-2001) including the 1997-1998 ENSO-drought. For 2.56ha of subplots, mortality and growth rates of small trees (10-<50cm gbh) were found also for two sub-periods (1996-1999, 1999-2001). A total of c. 19K trees were recorded. Mortality rate increased by 25% while both recruitment and relative growth rates increased by 12% for all trees at the coarse scale. For small trees, at the fine scale, mortality increased by 6% and 9% from pre-drought to drought and on to ‘post-drought' sub-periods. Relative growth rates correspondingly decreased by 38% and increased by 98%. Tree size and topography interacted in a complex manner with between-plot differences. The forest appears to have been sustained by off-setting elevated tree mortality by highly resilient stem growth. This last is seen as the key integrating tree variable which links the external driver (drought causing water stress) and population dynamics recorded as mortality and recruitment. Suitably sound measurements of stem girth, leading to valid growth rates, are needed to understand and model tree dynamic responses to perturbations. The proportion of sound data, however, is in part determined by the drought itself