pdf How reindeer grazing affects oroarctic fen vegetation? Popular

Tiina Kolari
University of Eastern Finland

Vegetation responses to reindeer grazing are variable and largely determined by vegetation type. Major part of research has focused on impacts of reindeer grazing on dry heaths and meadows, while mire habitats are less studied.
This study was carried out in a treeless oroarctic study area across the border of Finland and Norway (68°49', 23° 49'). We studied the effects of 1) a 13-year exclusion of reindeer summer grazing and 2) long-term (c. 55 years) difference in grazing between Finland (summer grazing) and Norway (winter grazing) on fen vegetation. One characteristic feature of the studied fens is abundance of Salix lapponum, a willow species subject to summer grazing by reindeer. We hypothesized that after a 13-year period of reindeer exclusion, plant community structure in fenced plots is similar to winter-grazed fens in Norway. In addition, we expected that willows grow taller and produce more fruits inside the fenced plots.Vegetation patterns and the main directions of anticipated change were analyzed with non-metric multivariate ordination (NMDS) using 2002 and 2015 subplot-level species cover data. We tested the effects of grazing on S. lapponum height and cover with linear mixed effects model using data from 2002, 2006 and 2015. The fruiting of S. lapponum in response to grazing pressure was studied in 2015.
In ordinations, grazing treatments were widely overlapping, and no uniform direction of change in vegetation was found. Fenced and summer grazed subplots together differed from winter grazed and, thus, legacy of summer grazing on mire plant communities was still apparent over a decade after reindeer exclusion. There was some distinction between winter-grazed subplots and all subplots in Finland, as winter-grazed subplots had less variation in NMDS. High abundance of Salix lapponum, Potentilla palustris and hepatics characterized winter-grazed subplots, while dwarf-shrubs were more common in the Finnish side of the border. We found significant differences in height and cover of S. lapponum between grazing treatments and years. Willows in Norway and in fenced plots were significantly more abundant, grew taller, and female plants had heavier and more frequent fruit bodies than in summer-grazed subplots.
In oroarctic mires, reindeer summer grazing affects S. lapponum stands. Northern mires are large carbon storages, and reindeer grazing may alter carbon cycling in mires via affecting on shrub abundance. The longer-term role of mammal herbivory in arctic mires is, however, still uncertain and the issue should be considered in Arctic research.