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Authors: Tage Vowles, Bengt Gunnarsson, Ulf Molau, Thomas Hickler, Leif Klemedtsson, Robert G. Björk
One of the most palpable effects of warming in Arctic ecosystems is shrub expansion above the tree line. However, previous studies have found that reindeer can influence plant community responses to warming and inhibit shrubification of the tundra.
In this study, we revisited grazed (ambient) and ungrazed study plots (exclosures), at the southern as well as the northern limits of the Swedish alpine region, to study long-term grazing effects and vegetation changes in response to increasing temperatures between 1995 – 2011, in two vegetation types (shrub heath and mountain birch forest).
We found that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. But although tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures, the overriding vegetation shift across our sites was a striking increase in evergreen dwarf shrubs, which were not influenced by grazing. Since the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.
Reference: Vowles, T., B. Gunnarsson, U. Molau, T. hickler, L. Klemedtsson, R.G. Björk. 2017. Expansion of deciduous tall shrubs but not evergreen dwarf shrubs inhibited by reindeer in Scandes mountain range. Journal of Ecology DOI: 10.1111/1365-2745.12753.
Photo: Tage Vowles, University of Gothenburg