Additive Partitioning of Diversity Reveals No Scale-dependent Impacts of Large Ungulates on the Structure of Tundra Plant Communities
- 348 Downloads
Large herbivores can change ecosystem functioning by impacting plant diversity. However, although such impacts are expected to be scale-dependent in ecosystems with wide-roaming ungulates, scaling issues rarely enter empirical assessments. We here test the hypothesis that the impact of increased reindeer abundance on plant diversity in alpine tundra is scale-dependent. Based on potentially high productivity of the focal habitat units and hence the possibility of positive grazer impacts on plant diversity we predicted higher α and β diversity at the habitat scale where reindeer densities are high. We also explored whether there were differences in diversity patterns at larger scales, including the scale of reindeer management districts. We estimated grazing disturbance as high versus low reindeer density in selected districts (a total extent of 7421 km2) of Northern Norway where reindeer-induced vegetation shifts are debated. We focus on dominance patterns because they can quantify the vegetation state and thus performed additive partitioning of Simpson diversity on multiple scales assessing also species’ contributions to diversity. Contrary to our predictions, we found only weak scale-dependent effects of reindeer grazing on plant diversity. Under high reindeer densities there was evidence for a landscape-scale homogenization of the vegetation, but the predicted α and β diversity increases at the habitat scale were not found. Consistently through all scales considered, four shrub species contributed the most to plant diversity. These results contradict the idea that reindeer at high stocking densities induce shifts in plant species dominance in productive habitats. We conclude that context-dependencies such as spatial scales of management units and habitat types need to be explicitly considered in evaluations of the impacts of large ungulates on plant diversity.
Keywordsgrazing tundra ecosystem shrub dominance abundant reindeer productivity gradients landscape elements management scale Fennoscandia
We would like to thank Raphaël Pélissier for valuable comments on an earlier draft of this article; Johan Olofsson, Rene Van der Wal, and one anonymuous referee for constructive criticisms; the Norwegian Coast Guard, Mette Nielsen, Tina Dahl, and Alina Evans for field assistance; Asle Lilletun for technical assistance; and participants in the project “Ecosystem Finnmark” for discussions. This study is a contribution from the “Ecosystem Finnmark” project and was financed by the Norwegian Research Council.
- Aerts R, Chapin FS. 2000. The mineral nutrition of wild plants revisited: A re-evaluation of processes and patterns. Adv Ecol Res 30(30):1–67.Google Scholar
- Anonymous. 2003. Ressursregnskap for reindriftsforvaltningen. Alta, Norway (in Norwegian): Reindriftsforvaltningen.Google Scholar
- Bardgett RD. 2005. The biology of soil—a community and ecosystem approach. Oxford: Oxford University Press.Google Scholar
- Billings WD. 2000. Alpine vegetation. In: Barbour MG, Billings WD, Eds. North American terrestrial vegetation. Cambridge: Cambridge University Press. Google Scholar
- Bliss LC. 2000. Arctic tundra and polar desert biome. In: Barbour MG, Billings WD, Eds. North American terrestrial vegetation. Cambridge: Cambridge University Press. Google Scholar
- Bye K, Nilsson E, Ekendahl B, Warenberg K. 1997. Flora i reinbeiteland. Landbruksforl. (in Norwegian): Nordisk organ for reinforskning.Google Scholar
- RI ES. 2004. Geoprocessing in ArcGIS. Redlands, CA: Environmental Systems Research Institute.Google Scholar
- Hester AJ, Bergman M, Iason GR, Moen J. 2006. Impacts of large herbivores on plant community structure and dynamics. In: Bergström R, Duncan P, Pastor J, Danell K, Eds. Large herbivore ecology ecosystem dynamics and conservation. Cambridge: Cambridge University Press. p 97–141.Google Scholar
- Lid J, Elven R, Lid DT. 1994. Norsk flora. Oslo (in Norwegian): Det norske samlaget.Google Scholar
- Magurran AE. 2004. Measuring biological diversity. Malden, MA: Blackwell Publ.Google Scholar
- Moen A, Odland A, Lillethun A. 1999. Vegetation. Hønefoss, Norway: Norwegian Mapping Authority.Google Scholar
- Muga DA. 1986. A commentary on the historical transformation of the Sami communal mode of production. J Ethn Stud 14:111–21.Google Scholar
- Olofsson J, Oksanen L. 2005. Effects of reindeer density on vascular plant diversity on North Scandinavian mountains. Rangifer 25:5–18.Google Scholar
- Olofsson J, Oksanen L, Callaghan T, Hulme PE, Oksanen T, Suominen O. 2009. Herbivores inhibit climate-driven shrub expansion on the tundra. Glob Chang Biol (in press).Google Scholar
- Pastor J, Cohen Y, Hobbs NT. 2006. The roles of large herbivores in ecosystem nutrient cycles. In: Danell K, Bergström R, Duncan P, Pastor J, Eds. Large herbivore ecology, ecosystem dynamics and conservation. Cambridge: Cambridge university press. p 289–325.Google Scholar
- R Development Core Team. (2006) R: a language and environment for statistical computing. R Foundation for Statistical Computing. http://www.R-project.org/.
- Shadish WR, Cook TD, Campbell DT. 2002. Experimental and quasi-experimental designs for generalized causal inference. Boston: Houghton Mifflin.Google Scholar
- Tybirk K, Nilsson MC, Michelson A, Kristensen HL, Shevtsova A, Strandberg MT, Johansson M, Nielsen KE, Rils-Nielsen T, Strandberg B, Johnsen I. 2000. Nordic Empetrum dominated ecosystems: function and susceptibility to environmental changes. Ambio 29:90–7.Google Scholar
- Vistnes I, Nelleman C. 2002. Avoidance of cabins, roads and power lines by reindeer during calving. Reindeer as a keystone species in the north—biological, cultural and socio-economic aspects, Arctic Centre Reports 38. University of Lapland, Rovaniemi. pp 113–123.Google Scholar