Habitat divergence in sympatric Fagaceae tree species of a tropical montane forest in northern Thailand

Abstract

Spatial distributions of many tropical trees are skewed to specific habitats, i.e. habitat specialization. However, habitats of specialist species must be divergent, i.e. habitat divergence, to coexist in a local community. When a pair of species specialize in the same habitat, i.e. habitat convergence, they could not coexist by way of habitat specialization. Thus, analyses of habitat divergence, in addition to habitat specialization, are necessary to discuss coexistence mechanisms of sympatric species. In this study, the habitat specialization and habitat divergence along topographic gradients of eight sympatric tree species of the Fagaceae were studied in a 15-ha study plot in a tropical lower montane forest in northern Thailand. A statistical test with torus shift randomizations for 9673 trees of Fagaceae revealed significantly biased distributions for all of the species, for at least one of the four topographic variables used: elevation, slope inclination, aspect and convexity. Slope convexity was the most critical topographic variable, along which all but one species had significantly skewed distributions. Out of 112 possible combinations of species pairs and topographic variables, 18 (16%) and two pairs (1.8%) showed significant habitat divergence and habitat convergence, respectively. The observed habitat divergence alone could not completely explain the coexistence of the eight species. There was a gradation in the habitat position of each species, with relatively large overlaps between species distributed in similar habitats, and small overlaps between species associated with contrasting habitats, respectively. The gradual changes in the habitats of the species suggested that dividing the species into a small number of distinct habitat groups, such as ridge and valley specialists, would not be straightforward.

Tree species diversity and utilities in a contracting lowland hillside rainforest fragment in Central Vietnam

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Establishing a long-term permanent plot in remnant forest of Cibodas Botanic Garden, West Java

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Comparison of statistical tests for habitat associations in tropical forests: A case study of sympatric dipterocarp trees in a Bornean forest

“…In this paper, we refer to a species that shows a significant habitat association as ''a specialist species'' or merely ''a specialist,'' and one that shows non-significant habitat association as ''a generalist species'' or ''a generalist.'' Examples of the use of this test can be found in Cannon and Leighton (2004) and Noguchi et al (2007). The Tree-density test is a modified version of the Torustranslation test of Harms et al (2001).…”

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