Charlie J. Gardner, James M. Bullock

Climate change is driving the rapid reorganisation of the world’s biota as species shift their ranges to track suitable conditions, however habitat fragmentation and other barriers hinder this adaptive response for species with limited dispersal ability. The translocation of species into newly suitable areas to which they are unable to disperse naturally has been suggested to conserve species threatened by climate change, but has not been widely adopted because the deliberate introduction of non-native species poses invasion risks and runs counter to traditional conservation approaches and philosophies. Using the future of forest ecosystems in the British Isles as a thought experiment, we argue that mass-scale assisted colonisation will be required not to conserve threatened species, but for the maintenance of functional ecosystems themselves. As climate changes, existing forest plant and animal communities of northern Europe will increasingly die out. On the mainland they will be somewhat replaced by analogous species from further south, but in Great Britain this replacement will be limited to a subset of mobile species due to the ocean barrier. As a result, forests there will lack many important component species unless these are actively translocated, will have reduced resilience and adaptive capacity, and will eventually collapse. Given the need for functional ecosystems in a hotter and highly fragmented world, conservationists must shift from trying to prevent change to trying to shape the biotic changes that are now inevitable. We must shift from reactive to proactive approaches in order to facilitate the emergence of robust novel ecosystems.