Shallow environmental gradients put inland species at risk: Insights and implications from predicting future distributions ofEucalyptusspecies in South Western Australia

Abstract

As climate changes, tree decline in Mediterranean-type ecosystems is increasing worldwide, often due to decreased effective precipitation and increased drought and heat stress, and has recently been observed in coastal species of the iconic Eucalyptus (Myrtaceae) genus in the biodiversity hotspot of south-west Western Australia. To investigate how this drought-related decline is likely to continue in the future, we used species distribution modelling techniques to generate broad-scale predictions of future distribution patterns under three distinct projected climate change scenarios. In a moderate climate change scenario, suitable habitat for all species was predicted to decrease by, on average, 73% by the year 2100, with most receding into southern areas of their current distribution. Although the most severe Eucalyptus declines in south-west Western Australia have been observed in near-coastal regions, our predictions suggest that inland species are at greater risk from climate change, with six inland species predicted to lose 95% of their suitable habitat in a moderate change scenario. This is due to the shallow environmental gradients of inland regions causing larger spatial shifts of environmental envelopes, which is likely to be relevant in many regions of the world. The knowledge gained suggests that future research and conservation efforts in south-west Western Australia and elsewhere should avoid focussing disproportionately on coastal regions for reasons of convenience and proximity to population centres, and properly address the inland region where the biggest future impacts may occur.