Impact of grazing and neighbour removal on a heath plant community transplanted onto a snowbed site, NW Finnish Lapland

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A transplant experiment was carried out to test hypotheses on forces organizing plant communities in a mountain snowbed. Particularly the roles of competition and grazing, as determinants of snowbed vegetation composition were examined. Blocks of heath vegetation dominated by Vaccinium myrtillus, a deciduous-evergreen dwarf shrub, were transplanted into a snowbed site near the altitudinal distribution limit ofV. myrtillus. Experimental treatments on the snowbed included grazer exclosures and neighbour removal. V. myrtillus declined in the snowbed as compared to controls during seven growing seasons. Removal of competing plants did not have significant effect on the projected plant area of V. myrtillus. Grazing tended to reduce the area of V. myrtillus with ca 40% when compared to exclosures. In contrast toV. myrtillus, graminoids, such as Deschampsia flexuosa, increased in the snowbed, presumably due to increased moisture from melting snow. A tall herb (Solidago virgaurea), virtually absent initially, started to increase within exclosures but not in unfenced plots. It cannot be ruled out that in the long term, tall, broad-leaved herbs can assume dominance on moderate snowbeds in the absence of grazing. The results suggest that the harsh snowbed environment is a major cause for the decline of V. myrtillus, and grazing may promote this decline. This is partially compatible with Grime's CSR hypothesis, but supports also the prediction of the exploitation ecosystems hypothesis that grazing limits potentially competitive species, and release from grazing leads to their increase.

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