Topographic species–habitat associations of tree species in a heterogeneous tropical karst seasonal rain forest, China
Aims: Tropical and subtropical karst forests of south China are under increasing pressure from over-exploitation causing widespread habitat degradation and biodiversity loss. Previous research has demonstrated that topography, as a proxy for resource availability, plays an important role in shaping tree species distributions in tropical forests. However, the association between growth stages and habitats types has not been considered in this analysis. Our aim was to examine the differences among different habitat types to determine whether tree species show similar species–habitat associations at young and mature life stages.
Methods: We used multivariate regression tree analysis to examined species–habitat associations among eight topographically defined habitats. The results were tested with a torus-translation test and canonical correspondence analysis (CCA) for 74 species in a 15 ha karst tropical seasonal rain forest at the Nonggang National Natural Reserve in south China. We considered two life stages (young and mature) of trees species that showed a positive association with topography.
Important Findings: We found marked differences in community characteristics and number of associations among the eight habitats. Of the 74 species subjected to torus-translation test, 63 had significant positive and 70 had significant negative associations with one or more of the eight habitats. Positive associations were more frequent in higher elevation habitats and negative associations were more frequent in lower elevation habitats. This suggests that edaphic and hydrological variation related to topography play important roles in habitat partitioning in heterogeneous karst forests. For the 63 tree species with significant positive associations to at least one habitat, 40 of them had the same positive association at young and mature life stages. The CCA revealed that the six topographic variables considered had consistent relationships with species distribution among all individuals and their two life stages. This indicates that most of the karst forest tree species show consistent associations with a single habitat throughout their life. We conclude that niche differentiation plays an important role in maintaining the diversity of this heterogeneous species-rich karst forest.