Climatic disequilibrium threatens conservation priority forests.

We test the hypothesis that climatic changes since 1800 have resulted in unrealised potential vegetation changes that represent a ‘climatic debt’ for many ecosystems. Caledonian pinewoods, an EU priority forest type, are used as a model system to explore potential impacts of two centuries of climatic change upon sites of conservation importance and surrounding landscapes. Using methods that estimate topographic microclimate, current and pre-industrial climates were estimated for 50 m grid cells and simulations made using a dynamic vegetation model. Core Caledonian pinewood areas are now less suitable for growth of pine and more favourable for oak than in 1800, whereas landscapes as a whole are on average more favourable for both. The most favourable areas for pine are now mainly outside areas designated to conserve historical pinewoods. A paradigm shift is needed in formulating conservation strategies to avoid catastrophic losses of this habitat, and of many others globally with trees or other long-lived perennials as keystone species