Lichens in times of climate change – impacts and responses especially in boreal and polar ecosystems

Climate change and biodiversity loss are among the most pressing issues of our time. Lichens have been shown to be sensitive to climate change, but responses are species-specific and contradictory trends have been reported. This review addresses lichen biology in relation to climate change and we overview the responses of lichens (e.g. biotic interactions, species distribution shifts and lichen acclimatisation, adaptation and extinction) to climate (e.g. temperature, precipitation, CO₂-levels, snow). Research shows mainly adverse or alarming effects of climate change on lichens, but there is not yet a generalisable understanding of the topic. We argue that contradictory trends emerge partly because relatively few studies have been conducted and they encompass a variety of locations, taxa, and methods, which makes them difficult to compare. Moreover, many aspects of lichens are still insufficiently understood, including species diversity, distributions, functional traits and biotic interactions with other organisms. We highlight that future studies would benefit from: 1) Developing a set of model species and also embarking full community studies; 2) Better species data, including monitoring programmes and trait data; 3) Improved conservation planning and Red List evaluations and 4) Acknowledging that lichens are small ecosystems and climate change may affect the partners in ways we do not understand yet.