Assessing Species Vulnerability to Climate Change in Tropical Asia: Implications for Biodiversity Conservation and Forest Management

Abstract

Global climate change is significantly altering the large scale distributions of plants and animals. The Earth has warmed by 0.7°C during the last century. The consequences are already apparent in forest ecosystems as species are responding to the changing climate with shifts in their phenology and geographic distributions. The potential for large increases in global mean temperatures (e.g., 4.3 ± 0.7°C) by 2100 has significant implications for forest species and ecosystems. Under these varying climatic conditions, some species may go extinct either locally or regionally, with climate change acting synergistically with other extinction drivers. Tropical Asian forests contain several biodiversity hotspots and species-rich ecoregions. Our understanding of species’ and forest ecosystems’ vulnerability to global climate change in this region is limited. Addressing this problem is a critical task for current tropical Asian ecological research.The overall aim of this PhD thesis is to investigate the current and potential effects of climate change on the geographic distribution and composition of selected plant and mammal species in tropical Asian forests. The selected plants include Sal (Shorea robusta), Garjan (Dipterocarpus turbinatus) and Teak (Tectona grandis). These all are ecologically and economically important timber trees and are distributed widely across South and Southeast Asia. The selected mammals include Asiatic black bear (Ursus thibetanus), Asian elephant (Elephas maximus), Western hoolock gibbon (Hoolock hoolock) and Bengal tiger (Panthera tigris tigris). These threatened large mammals are of high conservation concern and are typically targeted by international conventions. I present a comprehensive review of the previous literature and new predictive models of species distributions that quantify potential climate change impacts on tropical forests. My results show that projected changes in temperature and rainfall extremes are potential threats to the diverse and species-rich forest ecoregions of tropical Asia.I used bio-climatic models and two scenarios of climate change (a moderate and an extreme Representative Concentration Pathway (RCP) scenario) to assess climate change impacts on the continental scale distributions of two threatened Dipterocarp trees Sal and Garjan, and the valuable timber species, Teak. Annual precipitation was the key bioclimatic variable for explaining the current and future distributions of Sal and Garjan. Suitable habitat conditions for Sal will decline by 24% and 34% by 2070 under the RCP4.5 and RCP8.5 scenarios, respectively. In contrast, the consequences of climate change appear less severe for Garjan, with a decline of 17% and 27% under RCP4.5 and RCP8.5, respectively. Changes in annual precipitation, precipitation seasonality and annual mean actual evapotranspiration may result in shifts in the distributions of Teak across tropical Asia. These findings can contribute to conservation planning for the species and their management under future climates.I developed habitat suitability models for the four large threatened mammals (Asiatic black bear, Asian elephant, Western hoolock gibbon and Bengal tiger), across their entire distributions in Asia. The results suggest that changes in annual precipitation, annual mean temperature, precipitation and temperature seasonality, and land use/land cover change could reduce suitable habitat for these large mammals and therefore increase their extinction risks. It can be concluded that increasing climate stress on tropical forests could lead to greater extinction risks of these threatened large mammals.The findings of this thesis provide a fundamental basis for further studies of climate change impacts on species distribution in tropical Asia, and highlight the conservation importance of the plant and animal species in the region. The modelling outputs can be used to categorize the natural habitats of Sal, Garjan and Teak as low to high risk under changing climates to inform conservation planning and forest management. Given the conservation importance of the threatened large mammals for maintaining a healthy forest ecosystem, the findings of the models can be used to categorize the likely suitable habitats under changing climates and preparing proper guidelines to reduce their extinction risks. To ensure wider applicability to conservation planning for species vulnerable to global climate change, the methods and analyses presented here for tropical Asia could be applied to other tropical regions (i.e., in Africa and the Americas), using different species groups and forest types.