Abstract
AbstractCaribou (Rangifer tarandus) rely on the short Arctic growing season to restore body condition, support the demands of lactation, and prepare for the long arctic winter, making them susceptible to even small changes in forage availability or quality. Body condition in the summer and autumn is linked to winter survival rates and fecundity in cows, critical factors in the productivity of caribou populations. Climate change predictions of warmer and wetter northern winters suggest increased snowfall over Alaska's North Slope, which has recently been verified between 1995 and 2017. However, a comprehensive analysis of how deeper snow will affect caribou forage quality is absent across Alaska. In this study, we quantify how snow depth alters the quality and seasonality of caribou forage using a long‐term (24 yr) International Tundra Experiment snow depth manipulation to evaluate how winter climate change scenarios may affect tussock tundra systems in northern Alaska. Deeper snow in prior winters leads to increases in growing season leaf N and digestible protein (DP) in deciduous shrubs (Salix spp. and Betula spp.) and graminoids (Carex spp. and Eriophorum spp.), but not evergreen dwarf shrubs (Rhododendron spp. and Vaccinium spp.). Dry matter digestibility varied among species with small differences (<5%) associated with snow depth. Most striking was the discovery that deeper snow in the prior winter increased the duration of DP levels above the minimum threshold for protein gain in caribou by as much as 25 d in Salix pulchra and 6–9 d in Betula nana and Carex bigelowii in late summer and early autumn. Consequently, deeper winter snow may provide an extended window of opportunity for foraging and the accumulation of lean body mass and fat reserves which promote winter survival and successful calving the following spring and potentially improve the productivity of caribou in northern Alaska.
Highlights
Caribou and reindeer populations in the circumpolar Arctic face many challenges
The site is located within the home range of the Central Arctic Herd of caribou (Rangifer tarandus granti) on Alaska’s North Slope and is dominated by the tussock-forming sedge, Field sampling To test whether long-term differences in winter snow depth affect summer forage quality, we collected samples of six common plant species in moist-acidic tussock tundra during the growing season of 2017 and 2018
Increased snow depth had the strongest effect on the deciduous shrub and graminoid functional groups
Summary
Caribou and reindeer populations in the circumpolar Arctic face many challenges. Forage quality, predation, insect harassment, increasing human development, and extreme weather events have all been suggested as possible reasons for the declines of caribou and reindeer populations around the world in recent decades (Morschel and Klein 1997, Festa-Bianchet et al 2011, Fauchald et al 2017, Johnson et al 2019). Changes in the Arctic’s weather patterns and overall climate present additional challenges to caribou and reindeer populations (Loe et al 2020). Warmer weather during the growing season may decrease leaf-level nitrogen (N) and increase concentrations of antiherbivory compounds in spring and summer forage (Jonasson et al 1986, Turunen et al 2009, Zamin et al 2017). Mismatches in the summer and fall may have the potential to severely impact both individuals and populations due to the influence of small changes in forage intake and weight gain during this critical period on growth rates and fecundity (White 1983, Cebrian et al 2008, Proffitt et al 2016, Gustine et al 2017)
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