Temporal context affects the observed rate of climate‐driven range shifts in tree species

Aim Range shifts associated with 20th‐century warming have been documented for a wide range of taxa, but many species are not migrating fast enough to keep pace with the rapidly changing climate. Tree species can experience particularly long time lags in their migration response, resulting in altered forest composition and potentially delaying the migration of other obligate species. Here we review potential causes of these time lags and develop a conceptual framework for understanding how migration timing affects the observed rate of change. Location Global forest ecosystems. Methods We synthesize evidence from present‐day tree species migrations to determine how different migration constraints can delay tree species range shifts. Results The rate of present‐day tree migrations is frequently slower than expected, and many factors may contribute to observed migration lags. Migration constraints can be overcome given the right combination of circumstances, resulting in episodic range shifts that create temporal variability in migration rates. Given projected increases in forest disturbances and extreme climatic events, episodic range shifts are likely. Main conclusions Recent efforts to explain the slow rate of tree migration have primarily focused on dispersal limitation and niche‐based constraints such as competition and other biotic interactions. We argue that these constraints cannot be fully understood without considering the temporal context of tree migration. Attempts to forecast and manage future distribution shifts must consequently consider how migration timing may affect observed patterns of change.