reindeer – The Herbivory Network

One of the most palpable effects of warming in Arctic ecosystems is shrub expansion above the tree line. However, previous studies have found that reindeer can influence plant community responses to warming and inhibit shrubification of the tundra.

In this study, we revisited grazed (ambient) and ungrazed study plots (exclosures), at the southern as well as the northern limits of the Swedish alpine region, to study long-term grazing effects and vegetation changes in response to increasing temperatures between 1995 – 2011, in two vegetation types (shrub heath and mountain birch forest).

We found that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. But although tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures, the overriding vegetation shift across our sites was a striking increase in evergreen dwarf shrubs, which were not influenced by grazing. Since the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.

Reference: Vowles, T., Gunnarsson, B., Molau, U., Hickler, T., Klemedtsson, L., Björk, R.G. (2017) Expansion of deciduous tall shrubs but not evergreen dwarf shrubs inhibited by reindeer in Scandes mountain range. Journal of Ecology 105(6):1547-61. DOI: 10.1111/1365-2745.12753.

Picture: Reindeer exclosures in the Scandes mountains (photo: Tage Vowles, University of Gothenburg)

According to oral histories collected among fully nomadic tundra Nenets on Yamal Peninsula in West Siberia, extreme weather (rain-on-snow) events resulting in significant mortality within tundra herds have occurred roughly once per decade during the past century.

The extreme weather events of November 2006 and 2013 caused mass reindeer starvation that we were able to track in detail using state-of-the-art satellite sensors. The most recent rain-on-snow event of November 2013 resulted in ca. 61,000 reindeer deaths, about 22% out of 275,000 reindeer on the Yamal Peninsula at the time. Empirical data and modelling efforts for the events in 2006 and 2013 found that the likely trigger was brief periods of significant Barents and Kara sea ice retreat during early November. Relatively warm, open water and fragmented ice allowed high levels of atmospheric humidity to develop, while onshore winds combined with anomalously high November air temperatures led to eventual rainfall over extensive continental areas in the Nenets and Yamal-Nenets Autonomous Okrugs.

Socio-economic and ecological implications of the 2013-14 event will play out for years to come. The herders who lost their reindeer through starvation have resorted to full-time fishing in situ, while also borrowing breeding stock to rebuild their herds. In the meantime, northern Yamal pastures that are normally subject to intense grazing pressure in summer will likely experience less grazing and trampling.

Reference: Forbes, B.C., Kumpula, T., Meschtyb, N., Laptander, R., Macias-Fauria, M., Zetterberg, P., Verdonen, M., Skarin, A., Kim, K.Y., Boisvert, L.N. and Stroeve, J.C. (2016) Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia. Biology Letters 12(11):20160466.

Link to publication

Picture: Reindeer frozen into the snowpack in Spring 2014 (photo: Roma Serotetto)