How reindeer grazing affects oroarctic fen vegetation?

(Poster)

Tiina Kolari
tiina.kolari@uef.fi

Department of Environmental and Biological Sciences, University of Eastern Finland, Finland
,
Teemu Tahvanainen
Department of Environmental and Biological Sciences, University of Eastern Finland, Finland
,
Timo Kumpula
Department of Geographical and Historical Studies, University of Eastern Finland, Finland
,
Bruce Forbes
Arctic Centre, University of Lapland, Finland

DOI: 10.17011/conference/eccb2018/107732

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HOW REINDEER GRAZING AFFECTS OROARCTIC FEN VEGETATION?

Keywords: bryophytes, herbivory, mires, plant communities, Salix lapponum

Vegetation responses to reindeer grazing are variable and largely determined by vegetation type; however, major part of the research has focused on the impacts of reindeer grazing on dry heaths and meadows. Willow-dominated, peat-forming fens are important summer habitats for reindeer, but the effects of reindeer grazing on mires are not well known.

Our aim was to increase the knowledge concerning the long-term effects of reindeer grazing on fen vegetation. The study was carried out in a treeless oroarctic study area across the border of Finland and Norway (68°49', 23° 49'). One characteristic feature of studied fens is the abundance of Salix lapponum, a willow species subject to summer grazing by reindeer. Other dominant species include Eriophorum angustifolium, Carex rotundata and among mosses Sphagnum teres and Warnstorfia sarmentosa. We explored the effects of long-term (c. 55 years) difference in grazing between Finland (summer grazing) and Norway (winter grazing), and of 13-year exclusion of reindeer in Finland. Vegetation plot data sets were collected and heights of S. lapponum measured in 2002, 2006 and 2015. The fruiting of S. lapponum in response to grazing pressure was studied in 2015.

We found differences in abundance, plant size and fruiting of S. lapponum between grazing treatments. In non-grazed conditions, willows in Norway and in the exclosures were significantly more abundant, grew taller, and female plants had heavier and more frequent fruit bodies, than in the summer grazed plots. Our results showed no significant differences in species diversity between treatments or years, but DCA-ordinations of pin-point cover data revealed clear distinction between the Norwegian and Finnish fens. This mainly reflected differences in vascular plant community structure, while bryophyte communities had more overlap. The total cover of bryophytes was significantly higher in Norway. Ordinations did not clearly separate the summer grazed plots and the exclosures, and thus grazing may have legacy on mire plant communities still over a decade after reindeer exclusion.

In long-term, reindeer summer grazing affected especially S. lapponum stands and vascular plant community structure in oroarctic fens. Bryophyte communities appeared more resilient to the effects of grazing. Northern mires are large carbon storages, and reindeer grazing may interact with climate change and affect greenhouse gas balances in mires via plant community changes. The role of mammal herbivory in carbon cycle of arctic mires is, however, still uncertain.

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INTRO:
The research concerns an important applied aspect of management of natural resources in the Artcic - reindeer grazing and its influence on vegetation cover. Mires (fens with dominance of S. lapponum) were insufficiently studied for grazing impact on their dynamics before.
MERITS:
The manuscript has theoretical basis, clearly stated goals, methods and results. The last paragraph contains conclusions and future inquiry. The manuscript meets the requirements of a scientific publication (an abstract).
CRITIQUE:
The authors could consider improving English text, probably to ask for correction from an English-speaker. In my opinion, the results in the fourth paragraph could be formulated more clearly. For example: you said that cover of vascular plants revealed significant differences between treatments, while bryophyte communities more overlap; but the following sentence says that the total moss cover was significantly higher in Norway.
DISCUSSION:
The study explores long-term effects of different grazing treatments (summer vs. winter) compared to 13-years excluded areas and areas without grazing. Different components of vegetation cover were studied: shrubs, vascular plants and mosses. A sufficiently detailed method (pin-point) was to estimate the plant cover. Quantitative data were collected and statistical analyses applied (DCA, ordination) to reach reliable conclusions. Thus the study explores important ecological problems of vegetation successions under exploration from grazing in vulnerable Arctic ecosystems, and uses reliable tools to reach sound conclusions.

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INTRO:
~~The authors studied the long-term effects of reindeer summer grazing on vascular plant and bryophyte community structure in oroarctic fens. This was done by comparing fens from Finland (exposed to summer grazing), Norway (exposed to winter grazing), and from an area from which reindeers have been excluded for 13 years (in Finland). The study shows that especially vascular plant communities and Salix lapponum seem to be affected from summer grazing whilst bryophytes are more resilient.
MERITS:
~~The study uses multiple different data sets to tackle the question. This adds the reliability significantly. Moreover, the focus in long-term effects is valuable.
CRITIQUE:
~~There are no sample size (i.e. number of fens, number of study plots in each fens) mentioned. Also the sample size affects how reliable the results are, and whether they can be generalized.
DISCUSSION:
~~As already mentioned, adding the sample size would be great. Otherwise, I think the results are interesting and possibly valuable for determining how to mitigate the negative effects of reindeers on vegetation.