Ecosystem responses to reindeer grazing along the Scandinavian mountain range

• The warming of recent years has caused a shift in plant community structure in arctic areas and one of the most obvious changes is the expansion of shrubs. However, studies have found that reindeer can influence ecosystem responses to warming and inhibit shrub expansion. In this project we have revisited grazed (ambient) and ungrazed (fenced) study plots, at the southern as well as the northern limits of the Scandes mountain range, to investigate how the vegetation had changed in response to increasing temperatures between 1995 – 2012 occurring across the Scandes. Several plant communities within the Forest-Tundra Ecotone (FTE) were studied. Furthermore, we examined the impact of reindeer grazing on the production of extramatrical mycelia (EMM) and community structure of the ectomycorrhizal fungi using ingrowth mesh bags, nitrogen cycling using PRS-probes and fluxes of greenhouse gases. At shrub and grass heaths the evergreen shrubs nearly doubled from 1995-2012, whether grazed or not. Deciduous shrubs, too, showed a significant increase over time but, contrary to the evergreen shrubs, they also showed a positive effect of reindeer exclosure. Deciduous shrub cover had increased from 11% to 19% in ambient plots and 32% in fenced plots. Reindeer grazing was also found to significantly limit the advancement of tall (over 30 cm in height) dwarf birch and willow species at the grass meadow and shrub heaths. At the mountain birch forest sites, too, evergreen shrubs showed the greatest rise, increasing on average from 20% to 47% with no effect of reindeer exclosure, while the increase in deciduous shrubs was not as large as at the heath sites. Nor was there any treatment effect. The EMM production, at the shrub heath sites in the southern mountains, was 3 times larger in ambient plots than exclosures, which could be explained by a decreased abundance and an increased carbon (C) allocation to the roots of dwarf birch (Betula nana) when reindeer are present. However, this alteration of C did not affect the CO2 flux at the site, although the CO2 flux at the most productive site, grass meadow, showed a general pattern of lower fluxes from grazed plots. We conclude that shrub expansion is occurring rapidly in the Scandes mountain range. Reindeer, however, may restrain the expanding shrub cover and affect the C allocation in plants, in turn influencing the EMM production and in the longer term, potentially, the soil C budget.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

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