Borealization of terrestrial ecosystems: patterns, drivers and consequences

As the Northern latitudes of the planet warm, species are moving northward, a process that has been referred to as borealization. While this term has been mainly applied to the marine realm, similar patterns are described for terrestrial ecosystems but a common terminology is lacking. We define the term tundra borealization as shifts in species composition with climate change and land use change from the boreal forest into the tundra biome. Land use changes interact with climate change to lead to species and community reorganization in northern biomes, and borealization can have important consequences to food webs and ecosystem functions. There is growing evidence of borealization of plant and animal communities in tundra ecosystems and there are different methods that can be used to quantify borealization. Yet, metrics to assess borealization need to be standardized. Bringing together different definitions and lines of evidence for tundra borealization, we aim to emphasize this important ecological process and rapidly evolving area of research.