Boreal species are increasingly moving north into the Arctic, a process known as borealization. This shift is reshaping tundra ecosystems and could trigger cascading effects with profound impacts with profound impacts on Indigenous communities who depend on these landscapes.
Conducting plant studies in Kilpisjärvi, Finnish Lapland. Photo: Jiri Subrt
We tend to think that plants do not move, but they do, and they can transform an entire landscape. Today, a study led by the University of Edinburgh (UK) and CREAF (Spain) –and other centres including the Norwegian Institute for Nature Research (Norway)– warns plant species capable of living in both low-latitude tundra and boreal forests are gaining ground in the Arctic. Specifically, grasses and shrubs are the boreal species that tend to be the best colonisers, and the scientific team warns the advance of these species could have effects on the climate, wildlife and human communities. For example, lichens typical of the tundra are the main food source for caribou and reindeer: the problem is that under the shade of the shrubs lichens could recede and, if they decline, so too will the food supply for these animals. This, in turn, threatens the livelihoods of indigenous communities that depend on hunting and herding and also feed on some plants typical of the tundra.
The climate could also be affected by borealization. When shrubs and other woody species expand, they trap more snow in winter and cover the ground in summer. This changes the soil temperature and can accelerate the thawing of permafrost. As a result, large amounts of carbon that have been trapped for millennia in this “frozen refrigerator” would be released, contributing to global warming.
"In this study, we found that plants native to the boreal forest and the boreal-tundra transition zone are expanding into Arctic regions, although to varying degrees in different regions. The fact that parts of the Arctic are becoming more boreal could have cascading effects on tundra ecosystems", explains researcher Mariana García Criado, a Marie Skłodowska-Curie researcher at CREAF and the University of Edinburgh and lead author of the study.
Eurasia and alpine areas
The team has observed that borealization is most intense in the Eurasia region and in alpine areas, where the distance between the boreal forest and the tundra is shorter, “which facilitates seed dispersal”, according to García Criado. The expansion of boreal vegetation is also greater in the warmer and wetter areas of the Arctic, conditions that favour the establishment of plants.
So far, the scientists haven’t found a direct relationship with the increase in temperature in the areas studied, “probably because the greatest temperature rises occur at high latitudes where it is more difficult for boreal species to reach”, explains the researcher.
The study also analysed what characteristics make some plants spread more successfully than others. The scientific work found that shorter boreal species have an easier time advancing in the tundra than taller ones. In addition, grasses and shrubs colonised more plots than herbaceous species, thanks to their adaptive advantages, such as more efficient uptake of soil nutrients. Some examples of boreal species that managed to reach a large number of plots are the grass Carex bigelowii (Bigelow's sedge) and the shrub Vaccinium vitis-idaea (lingonberry).
Four decades of expeditions
To carry out the research, the team analysed data from the International Tundra Experiment (ITEX) consortium, which has been collecting information from permanent plots distributed throughout the Arctic for four decades. In total, more than 1,100 plots and 287 plant species have been studied, sampled between 1981 and 2023: “It is an extremely valuable network in terms of science and conservation, as so many years of fieldwork in this remote part of the world, using a similar methodology, are not common”, García Criado points out.
“The next step in this research is to study the impacts of the borealization process on ecosystems and on the Indigenous communities of the Arctic”, concludes Mariana García Criado. In addition, the researcher explains that she is also promoting a new line of research to find out how lichen and moss populations are changing in polar regions lichen and moss populations are changing in polar regions, “something that is still largely unknown”.
The study has been led by the University of Edinburgh and CREAF, with the participation of more than 30 research institutions from around the world. These includ the Agricultural University of Iceland and the University of Iceland (Iceland), the Norwegian University of Science and Technology, the Arctic University of Norway (UiT) and the University of Bergen (Norway), the University of Gothenburg and the Gothenburg Global Biodiversity Centre (Sweden), Vrije Universiteit Amsterdam (Netherlands), the University of British Columbia and the University of Waterloo (Canada), the University of Colorado Boulder and the USDA Forest Service (United States), as well as Aarhus University and the University of Copenhagen (Denmark), and the University of Helsinki together with the Natural Resources Institute Finland (Finland).
Reference article:
García Criado, M., Barrio, I.C., Speed, J.D.M., Bjorkman, A.D. et al. (2025). Borealisation of Plant Communities in the Arctic Is Driven by Boreal-Tundra Species. Ecology Letters 28:e70209 https://doi.org/10.1111/ele.70209