Environmental gradients structure tropical tree assemblages at the regional scale

Abstract

Questions Environmental filtering and niche differences influence assembly of tree communities at multiple spatial scales. At regional scales, determining the environmental variables that primarily influence compositional variation in species assemblages reveals ecologically relevant habitat types for conservation. Strength of species’ association with these habitats and differences in species occurrence along environmental gradients lend credence to niche‐based assembly and help estimate responses of tree communities to natural or human‐mediated environmental change. Location Western Ghats, India. Methods We analysed an openly available data set of ca. 62 000 trees (>10 cm DBH) in 96 1‐ha plots across a 22 000 km2 landscape, using multivariate regression trees (MRT) to identify compositional groups related to combinations of temperature, rainfall and soil type. Next, we conducted indicator species analysis to assess species associations with habitats. We then compared species richness and diversity among habitats. Finally, to discern niche overlap we assessed pair‐wise differences between species in their abundance distributions along environmental gradients. Results Environmental gradients clearly influenced landscape‐scale tree assemblages in this region. Nine ecological habitat types were identified: annual rainfall was the most important variable driving compositional differences, followed by temperature, seasonality and soils. Approximately 17% of 398 species tested were associated with single habitats. Number of species associations and local diversity varied significantly among habitats. Between 29 and 50% of species pairs showed significant differences in their distributions along environmental gradients considered. Conclusions Relating compositionally defined tree assemblages to combinations of abiotic variables allows ecologically robust recognition of habitat types for conservation planning. Compositional differences structured by annual rainfall and temperature suggests that climate change can impact species persistence and tree community composition in the Western Ghats. Specifically, future research should assess drought response of forests by examining recruitment and survival of species in different combinations of rainfall, temperature and human disturbances.

Functional trait and community phylogenetic analyses reveal environmental filtering as the major determinant of assembly of tropical forest tree communities in the Western Ghats biodiversity hotspot in India

“…Although, a few studies have evaluated the role of historical and environmental factors underlying the composition, distribution and abundance pattern of tropical tree species with contrasting leaf phenology. They have not integrated the ecologically important traits and evolutionary relationship of co-occurring species in an integrated ecological analysis (Ramesh et al 2010a(Ramesh et al , 2010bJoseph et al 2012;Van Ommen Kloeke et al 2012;González-Caro et al 2014;Lohbeck et al 2015;Krishnadas et al 2016;Ge and Xie 2017). Our results show that taxonomic turnover and phylogenetic structure of tree communities in the study region is best predicted by precipitation gradient followed by temperature related variables and aridity index.…”

The effect of environmental filtering on variation in functional diversity along a tropical elevational gradient

“…Species distributions have been examined along environmental gradients for decades. They provide great insight into the mechanisms of species diversity and community assembly processes in natural ecosystems (Krishnadas, Kumar, & Comita, ; Šímová et al., ). Functional traits characterize species’ unique ecological strategies: the difference in their responses to environmental change and their influence on ecosystem processes (Díaz & Cabido, ).…”

“…Species distributions have been examined along environmental gradients for decades. They provide great insight into the mechanisms of species diversity and community assembly processes in natural ecosystems (Krishnadas, Kumar, & Comita, 2016;Šímová et al, 2015).…”

Invasive alien plant species, fragmentation and scale effects on urban forest community composition in Durban, South Africa

“…The plot scale analysis determines which niche factors influence the establishment of invasive species while the patch scale analysis determines which landscape attributes facilitate or impede the establishment of those species. This shows the scale of influence in the establishment and distribution of species (Ersoy 2016;Krishnadas et al 2016).…”