Tree species of tropical and temperate lineages in a tropical Asian montane forest show different range dynamics in response to climate change

Abstract

Shifts in species distributions have been documented in response to recent climatic change, with most species moving poleward and to higher altitude. However, different taxa may respond to climatic change differently. The Climatic Variability Hypothesis (CVH) suggests that taxa originating from environmentally variable habitats, such as those at high latitudes and altitudes, should evolve wider environmental tolerances and greater dispersal capacity, and consequently be less responsive to climatic change than taxa originating from relatively stable habitats. However, empirical tests of this hypothesis, especially in the Asian tropics, are scarce. In this study, we assessed the range dynamics of 20 tree species, by using the abundance and mean tree diameter and the ratio of juveniles to trees along an altitudinal transect (2450 m–3070 m) in a montane forest located in the southeastern Himalayas in Myanmar. We also compared the suitable range sizes of tree species of different range dynamics category. Among the species investigated, 12 experienced significant upward range extensions and other eight species experienced no-upward extensions. The modeled distribution range size of the ‘upward species’ were marginally significant narrower than those of ‘non-upward’ species. The ‘upward’ species were also often species of tropical evolutionary origin and the ‘non-upward’ species were of subtropics and temperate origin. The mechanism behind these distribution patterns of different species may be complex while the distribution patterns of this 20 species along the altitudinal transect generally support the prediction of the CVH. From the perspective of conserving biodiversity against the impacts of climatic change, more attention needs to be paid to narrowly distributed species, which are typically tropical origin, by enhancing connectivity and dispersal capacity in fragmented landscapes.