Distribution patterns of two widespread, co-dominant savanna tree species of the Indian subcontinent under current and future climates

Abstract

Future climate is expected to alter the dynamics and distribution of vegetation. Here, we use ecological niche modelling to investigate the current and predicted future distributions of two dominant tree species that characterize the ecology and dynamics of the widespread tropical dry biomes of the Indian subcontinent- Terminalia anogeissiana (formerly and henceforth Anogeissus latifolia) and Terminalia elliptica (both Combretaceae). Using current occurrence data and six ecologically relevant climate variables, we find that, as expected, T. elliptica and A. latifolia share highly similar climatic niches with substantial overlap ([~]84%). Mean annual precipitation (MAP), mean temperature of the driest quarter (MTDQ), and temperature annual range (TAR) emerge as the key environmental variables explaining the distribution of both species, but their relative influence differs. T. elliptica appears to occur across a broader climatic niche that includes wetter areas with cooler dry seasons (lower MTDQ) and lower temperature annual ranges (TAR) relative to A. latifolia. Currently, the area of modelled suitable habitat for both species are vast (A. latifolia: 416,057 km{superscript 2}; T. elliptica: 401,544 km{superscript 2}). However, under future climate scenarios, both species are projected to incur dramatic losses of suitable habitat (A. latifolia: [~]63% by 2041-2060 and [~]84% by 2081-2100; T. elliptica: [~]57.8% by 2041-2060 and [~]73% by 2081-2100). By 2100, the Western Ghats are projected to remain as the last key refugia for both species, while vast other regions are likely to become increasingly unsuitable. Contrary to current understanding, our results underscore the high vulnerability of currently dominant tree species of the tropical dry biomes, through potential losses of suitable habitats under future climate regimes.