Exploring variation in the responses of tree species to climate across diverse montane forests in Taiwan

Abstract

Rapid climate change is impacting forest distribution, species composition and function globally. Although some overall patterns are emerging, many factors can interact with climate across different forest types and between individual trees, which can modify responses of trees to climate change. Our overall understanding of how forests are changing is incredibly limited, with a paucity of information from tropical and subtropical mountain regions. Given the need for substantial improvement to our understanding of the variation in responses of forests to climate change, this thesis sets out to evaluate our current knowledge and highlight the remaining gaps in our understanding. Specifically, this thesis aims to 1) determine the size and direction of species distribution shifts, 2) identify the extent to which tree functional traits are associated with distribution shifts and environmental variation, 3) quantify variation in functional traits across the elevation range of a widely distributed tree species (Pinus taiwanensis), and 4) quantify the variability in responses of the early stages of P. taiwanensis development to projected temperature changes. We found that high elevation species shifted upwards but below the treeline, species shifted individualistically. Individual functional traits were poor predictors of individual species distribution shifts, but relationships between environment and function at the community-level were strong. Overall functional trait variation was high across the elevation range of P. taiwanensis and higher temperatures reduced the time to seedling emergence and promoted biomass gain, with seed elevation of origin also highly influential. These findings highlight the substantial variability possible in plant climate relationships across a large elevational gradient spanning a broad range of forest types, highlighting that it should not be assumed that trees will react ‘as one’ to climate change. Ultimately, this information will allow improved estimation of the impacts of climate change on biodiversity and ecosystem function across tropical montane forests.