Category: NordBorn publications

The composition of tundra plant communities is rapidly changing due to climate change. The potential encroachment of boreal species, from warmer, southern latitudes, is a conservation concern. Using the ITEX+ database, in a paper recently published in Ecology Letters Mariana García Criado and collaborators synthesized data from 32 study areas across the Arctic, including 287 vascular plant species and 1,137 plots, resurveyed between 1981 and 2023.

The aim of the study was to (i) quantify the borealization of tundra plant communities, (ii) assess the biogeographical, climatic and local drivers of borealization, and (iii) identify species contributing to borealization and their associated traits.

They found that around half of the surveyed plots experienced borealization, understood as the increase in occurrence and abundance of boreal species or species present on the boreal-tundra boundary. Borealization was greater in Eurasia, closer to the treeline, at higher elevations, in warmer and wetter regions, where climate change was limited, and where initial boreal abundance was lower. Boreal colonizer species were generally short-statured, and more often shrubs and graminoids.

The findings of this study indicate that tundra borealization is mainly driven by the spread of boreal-low Arctic tundra species, which are already present in tundra landscapes. These changes in plant community composition can have cascading impacts on land-atmosphere interactions, trophic dynamics and Indigenous and local livelihoods.

Reference: García Criado, M., Barrio, I.C., Speed, J.D.M., Bjorkman, A.D.,  Elmendorf, S.C., Myers-Smith, I.H., Aerts, R., Alatalo, J.M., Betway-May, K.R., Björk, R.G., Björkman, M.P.,  Blok, D., Cooper, E.J., Cornelissen, J.H.C., Gould, W.A., Gya, R., Henry, G.H.R., Hermanutz, L.,  Hollister, R.D., Jägerbrand, A.K., Jónsdóttir, I.S., Kaarlejärvi, E., Khitun, O., Lang, S.I.,  Macek, P.,  May, J.L., Michelsen, A., Normand, S., Olsen, S.L., Post, E., Rinnan, R.,  Schmidt, N.M., Sjogersten, S., Tolvanen, A., Töpper, J.P., Trant, A., Vandvik, V., Vowles, T. (2025) Borealisation of plant communities in the Arctic is driven by Boreal-Tundra species. Ecology Letters. https://doi.org/10.1111/ele.70209

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The top picture shows a woolly willow (Salix lanata) growing in Latnjajaure, Sweden (credit Anne Bjorkman)

The spread of the beaver (Castor canadensis) into the Arctic tundra is a textbook example of the process of borealization. A new study by Ken Tape at the University of Alaska Fairbanks and James Speed at the Norwegian University of Science and Technology and a member of the NordBorN network, shows how temperature is a crucial factor determining the distribution of beavers and their impact on the whole ecosystem through dam building across the Alaskan tundra.

Temperature drives an increase in suitable habitat for beavers from 15 000 km² in the early 20^th century, to 30 000 km² at present, while future climatic warming is projected to increase the potential suitable habitat to between 100 000 and 150 000 km² by 2090.

Such a dramatic increase in distribution of an ecosystem engineering species is likely to have dramatic impacts on the future state of the tundra.     

The paper was recently published in Environmental Research Letters, and has been featured in Science.

Reference: Tape, K. D., & Speed, J. D. (2025). Predicted expansion of beaver pond distribution in Arctic Alaska, 1910–2090. Environmental Research Letters, 20(9), 094009. 10.1088/1748-9326/adeba2

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The picture shows a beaver modified habitat in Alaska (photo: Ken Tape, University of Alaska Fairbanks)

A recent paper from the Machine Vision for Natural History research group at NTNU University Museum, including several NordBorN members, reports on global trends in flowering phenology, an indicator of the impact of anthropogenic climate change. A machine learning model was used to examine more than 8 million images of herbarium specimens from around the world and spanning two centuries. High diversity in temporal trends in flowering seasonality was found across different ecoregions, with greater variability at low latitudes than at high latitudes. This likely reflects the effects of a combination of shifts in temperature and precipitation seasonality, together with lower photoperiodic constraints to flowering. The study demonstrates the utility of machine learning approaches in large-scale analysis of museum collections and underscores both the importance of natural history collections in assessing long-term trends and the need for digitization efforts to make such specimens available to researchers across the world.

Future work is planned to link global flowering phenology patterns with local climate data, and to examine borealization by combining analysis of historical museum collections with data from field studies. You can read the paper here.

Reference: Williamson, D.R., Prestø, T., Westergaard, K.B., Trascau, B.M., Vange, V., Hassel, K., Koch, W. and Speed, J.D., Long‐term trends in global flowering phenology. New Phytologist. https://doi.org/10.1111/nph.70139

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Image: Herbarium specimen of Leucanthemum maximum from the NTNU collection which was IDed by one of the co-authors