Visions from nature

Strange fences in the forest

By Anders L Kolstad
Picture showing how there's much denser vegetation inside, compared to outide, a fence which has excluded cervids for eigth years.
The strange fences in the forest are associated with clear differences in the vegetation. From Bratsberg, Trondheim. Photo: Audun Hageskal.


The beginning

Eight years ago some researchers at the NTNU University Museum and the Norwegian Institute for Nature Research (NINA) started erecting some strange, large, sturdy, fences throughout the Norwegian forest. For some time the fences stood there serving no apparent function. Someone probably wondered what sort or unconventional animal pen this was pretending to be. Gradually, however, the realization grew – the fence was not there to contain the animals, it was there to exclude them.

Large differences

It’s been 10 years since the first fences appeared and you don’t need any fancy statistics in order to appreciate the effect of the exclosure treatment. Inside the fence the growth of deciduous species such as rowan and birch has been much greater. The biggest differences are found at productive sites where the fences were built on recent clear-cuts. Here the rowan can be 4-5 meters tall today, whereas you really have to search vigorously in order to find any rowan outside the fence that has been able to stretch 50 cm (as chance has it, that’s also roughly the average snow depth in these parts).

Picture showing how dense the vegetation is inside the fence. Professor Gunnar Austrheim is trying to find a way through this joungle.
Where the moose can’t go, the broadleaves can grow. Professor Gunnar Austrheim is looking for a way through the dense jungle of rowan and birch. Photo: Audun Hageskal.


The Cervids and the Forest

It is the chronic browsing by cervids that has created this large difference we now observe across the fence. Moose, Red deer, and Roe deer, have increased drastically in numbers many places in Norway since around 1970. We will continue the work to explore the multiple effects of this herbivory on the development and the processes of the forest. Together with my supervisors James Speed, Gunnar Austrheim, Bente Jessen Graae and Richard Strimbeck, I am doing a PhD on this topic. It is incredibly exciting to attempt to piece together all the interactions of what is going on in this system, both above and below ground, and in the short and long term.

Visit the projects webpage and my PhD description page if you want more info.


Photo of Anders Lorentzen Kolstad
Anders Lorentzen Kolstad started his PhD in 2015 studying the effects of moose browsing on the boreal forest. Photo: Marte Fandrem. CC SA-BY 4.0.

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