Herbivores influence many aspects of ecosystems in Arctic and alpine tundra, from plant population dynamics and community composition to soil carbon storage and nutrient cycling. Herbivory is a multi-scale process, herbivores select their food at small spatial scales, but also at large spatial scales in terms of their ranges and distributions. We have a good understanding of how herbivores affect site level dynamics, but not larger scale dynamics. Indeed, while climatic variables have been successfully used to model species distributions, biotic interactions including herbivory have been notably absent from such approaches. However, a recent study seeks to change this.

A unique dataset

James Speed and Gunnar Austrheim from the NTNU University Museum at the Norwegian University of Science and Technology have published a paper in the journal Biological Conservation where they use a national-level data set mapping densities of all large herbivores to predict the distribution of rare plant species within Norway. The study focused on seven arctic and alpine tundra plant species on the Norwegian Red List for species, and the main herbivores grazing in these ecosystems – domestic sheep along with both wild and semi-domestic reindeer.

Considerable effect from herbivores

Although climatic variables were the most important factor in controlling the distribution of all seven species, there was a clear signal of herbivore densities influencing the distributions. This was most notable for Primula scandinavica (Scandinavian primrose). Low densities of herbivores were associated with low habitat suitability for this species. Speed and Austrheim mapped the regions of Norway where herbivore density was the factor most limiting the distribution of each rare plant species. There was little overlap in these areas between the seven plant species. This suggests that the management of herbivore populations for the conservation of rare plant species needs to be specific for each location and plant species.

Referanse: Speed, J.D.M. & Austrheim, G. (2017) The importance of herbivore density and management as determinants of the distribution of rare plant species. Biological Conservation, 205, 77-84.