Forest expansion threatens Arctic tundra ecosystems: A process-based modeling perspective

Arctic tundra ecosystems are changing fast due to warming and more intense land use. In the SQUEEZE project, which focuses on identifying key Arctic regions for nature conservation, we are using a process-based vegetation model called LiBry (currently configured for mosses and lichens) to see how forest expansion and climate change might affect tundra biodiversity and functions in the future. In our initial simulations, we compared treeline conditions in 2020 and 2300 under RCP8.5, keeping other climate variables the same so we could look at forest invasion specifically. We found a drop in non-vascular plant biomass (from 0.65 Gt to 0.51 Gt), net primary productivity (from 0.26 Gt yr^–1 to 0.19 Gt yr^–1), and functional diversity. This suggests that increased tree cover may reduce future diversity and productivity of tundra plant communities, which might impact crucial processes such as permafrost protection.

As a next step, we plan to include shrubs, grasses, and other vascular plants in LiBry, using trait data from sources including the TRY database. By considering different stressors — forest invasion, climate change, grazing, and fire management — our work will enable more informed decisions about conservation across the Arctic. These simulations will ultimately support TundraProtect, a conservation tool aimed at prioritizing key areas for protection while addressing increasing economic pressures in the Arctic.