Abstract
ABSTRACTShrubification of arctic tundra is a well-recognized phenomenon, and it can be particularly rapid in moist habitats. Reindeer grazing can inhibit shrubification, but grazing impacts on mire vegetation have been overlooked. We studied grazing effects on plant communities and Salix lapponum in oroarctic mires at the border of Finland and Norway. We compared plant community structure and S. lapponum abundance and traits between (1) grazed fens (Finland); (2) experimental exclosures (Finland), where reindeer have been kept out for 13 years; and (3) nongrazed fens (Norway). Grazing effect on shrubification was assessed using the Normalized Difference Vegetation Index (NDVI) and leaf area index (LAI). We did not find a uniform direction of vegetation change connected to the exclosure treatment, and grazing treatments were overlapping in multivariate ordination. Neither NDVI nor LAI indicated clear differences. Instead, significant results were revealed in total abundance of species groups and in S. lapponum traits. The cover of bryophytes was significantly lower under free grazing. Reindeer grazing reduced the abundance, height, and flowering and increased leaf N concentration of S. lapponum. We conclude that reindeer grazing controls willows and affects total abundance of important species groups, and plant community structure is resistant to grazing effects in oroarctic mires.
Highlights
A major part of the circumpolar arctic tundra and northern boreal regions is grazed and trampled by either semidomestic or wild reindeer (Rangifer tarandus) populations
We conclude that reindeer grazing controls willows and affects total abundance of important species groups, and plant community structure is resistant to grazing effects in oroarctic mires
All grazing treatments were overlapping (Figure 2), and we did not find any uniform directions of change in vegetation connected to the exclosure treatment; that is, the exclosure plots did not move toward nongrazed plots as expected (Appendix 4)
Summary
A major part of the circumpolar arctic tundra and northern boreal regions is grazed and trampled by either semidomestic or wild reindeer (Rangifer tarandus) populations. Reindeer grazing can increase nutrient cycling (Olofsson et al 2001; Stark, Strömmer, and Tuomi 2002) and cause transitions between alternative vegetation states (van der Wal 2006). Lichen cover and biomass tend to decrease in grazed areas (van der Wal, Brooker, et al 2001; den Herder, Kytöviita, and Niemelä 2003) because they are preferred winter forage for reindeer (Nieminen and Heiskari 1989) and are sensitive to trampling during snow-free seasons Nutrient-poor habitats, grazing results in transitions from a lichen-rich to a moss-dominated vegetation state (Manseau, Huot, and Crête 1996; van der Wal 2006). Though willows and sedges in peat-accumulating mires provide important forage in summer, little is known about grazing effects on mire vegetation
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