Category: NordBorn publications

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

NordBorN researchers have estimated and mapped historic biomass densities of large herbivores and carnivores across Norway. The current high densities of wild ungulates, especially moose and roe deer, contrast with historically high densities of livestock. Carnivores show a low level of recovery from near absence in the mid 20^th century. However, densities are far below where they were in the 19^th century.

These findings have implications for borealization: Previous studies have shown that herbivory can prevent the spread of boreal species into the tundra, yet it is clear that the trophic interactions involving large herbivores and carnivores are highly dynamic in both time and space.

Reference: Speed, J.D.M, Sobocinski, A., Kolstad, A. L., Linnell, J. D., Solberg, E. J., Mattisson, J., & Austrheim, G. (2025). The trophic distribution of biomass in ecosystems with co-occurring wildlife and livestock. Scientific Reports, 15(1), 1474. https://www.nature.com/articles/s41598-025-85469-2

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Photo: Lynx (Erik F. Brandsborg, CC BY-SA)