Climate, icing, and wild arctic reindeer: past relationships and future prospects

Abstract

Abstract. Across the Arctic, heavy rain-on-snow (ROS) is an ''extreme'' climatic event that is expected to become increasingly frequent with global warming. This has potentially large ecosystem implications through changes in snowpack properties and ground-icing, which can block the access to herbivores' winter food and thereby suppress their population growth rates. However, the supporting empirical evidence for this is still limited. We monitored late winter snowpack properties to examine the causes and consequences of ground-icing in a Svalbard reindeer (Rangifer tarandus platyrhynchus) metapopulation. In this high-arctic area, heavy ROS occurred annually, and ground-ice covered from 25% to 96% of low-altitude habitat in the sampling period (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010). The extent of ground-icing increased with the annual number of days with heavy ROS (!10 mm) and had a strong negative effect on reindeer population growth rates. Our results have important implications as a downscaled climate projection (2021-2050) suggests a substantial future increase in ROS and icing. The present study is the first to demonstrate empirically that warmer and wetter winter climate influences large herbivore population dynamics by generating ice-locked pastures. This may serve as an early warning of the importance of changes in winter climate and extreme weather events in arctic ecosystems.

Cratering behaviour and faecal C:N ratio in relation to seasonal snowpack characteristics in a High-Arctic ungulate

“…Insect harassment is minimal (Reimers 1980), as is interspecific competition: the Svalbard rock ptarmigan (Lagopus muta hyperborea) is the only other over-wintering herbivore. Survival and reproduction rates are highly variable between years (Solberg et al 2001;Stien et al 2012) because of density-dependence and variation in climatic conditions during winter (Reimers 1983;Aanes et al 2000;Solberg et al 2001;Kohler & Aanes 2004;Hansen et al 2011;Hansen et al 2013), but also during summer (Aanes et al 2002;Hansen et al 2013). …”

“…In the High Arctic, where vegetation is generally of very low stature, ground ice can completely cover the vegetation (Hansen et al 2010). Such feeding conditions can lead to starvation-related declines in winter body mass , survival (Solberg et al 2001) and fecundity (Stien et al 2012), with consequences for population dynamics (Parker et al 1975;Kohler & Aanes 2004;Grenfell & Putkonen 2008;Miller & Barry 2009;Hansen et al 2011;Hansen et al 2013).…”

Local and regional variability in snow conditions in northern Finland: A reindeer herding perspective

“…Ground ice formation prevents reindeer access to ground-growing lichens and has reported to cause catastrophic declines in populations of semi-domesticated (Helle 1980) and wild reindeer (Kohler and Aanes 2004;Tyler 2010;Hansen et al 2011Hansen et al , 2014. Mold formation on pastures was often related to snow cover formation on unfrozen ground, unstable weather in early winter and ground ice formations.…”

“…The amount of winter resource varies in the reindeer herding area due to natural variation in vegetation as well as other land use activities, such as commercial forest management, that can have negative impacts on the quantity and quality of lichen pastures (Kivinen et al 2010). Reindeer access to lichen resources is also related to snow and ice conditions, which can strongly vary within the winter season and between winters (Kohler and Aanes 2004;Hansen et al 2011).…”

“…Although the structure of snow cover is highly significant for reindeer and other northern animals, studies on snow structural properties are very limited in the circumpolar area. Further, earlier studies have mainly focused on the impacts of snow and ice on reindeer and caribou populations in treeless high-latitude regions (Miller and Barry 2009;Tyler 2010;Hansen et al 2011;. In this work, weather station measurements were used to force the SNOWPACK snow model and combined with reindeer herders' experiences to study the local and regional variations in snow conditions in boreal and subarctic zones in northern Finland over the past 30 years.…”