Whole range and regional‐based ecological niche models predict differing exposure to 21st century climate change in the key cool temperate rainforest tree southern beech (Nothofagus cunninghamii)

The warmer and drier climates projected for the mid‐ to late‐21st century may have particularly adverse impacts on the cool temperate rainforests of southeastern Australia. Southern beech (Nothofagus cunninghamii; Nothofagaceae), a dominant tree species in these forests, may be vulnerable to minor changes in its climate envelope, especially at the edge of the species range, with Holocene fossil evidence showing local extinction of populations in response to small climate changes. We modelled the stability of this species climate envelope using the maximum entropy algorithm implemented in Maxent and two thresholds of presence/absence by projecting the modern climate envelope onto four Global Circulation Models forecasted for two time periods (2050s and 2070s). The climate envelope, as estimated from the species present climatic range, is predicted to shrink by up to 49% by the 2050s and up to 64% by the 2070s. The greatest predicted reduction is in Victoria with 91–100% of its current range being climatically unsuitable by the 2070s. Climatically similar areas to the species present range are predicted to remain in mountainous areas of western Tasmania, the Northeast Highlands of Tasmania, and the Baw Baw Plateau in the Central Highlands of Victoria. However, region‐specific modelling approaches made very different predictions from the whole‐range based models, especially in the severity of the predicted decline for Victorian populations of N. cunninghamii which occur in much warmer climates than the rest of the species geographical range. This shows that, for widespread species that span a range of climate zones, the exposure of current populations to climate change may be better modelled using a regional based approach. How the species responds to climate change will depend on the species ability to respond to drier and warmer climates and the concomitant increase in fire intensity.