The Arctic is warming more rapidly than temperate zones leading to dramatic changes in Arctic ecosystem structure and function. Over recent decades warming has lead to a greening of Arctic systems and changes in many Arctic plant communities including expansion of shrubs. Furthermore, Arctic systems are becoming wetter with the potential for deeper snow in the future. These changes directly impact the feeding ecology of caribou (Rangifer tarandus), the most abundant large herbivore in the system, by altering the quantity of preferred forages and potentially the protein content and digestibility of leaf tissue. Here we report on experimental and observational differences in tissue N and fiber content of common Arctic species including diamond-leaf willow (Salix pulchra), dwarf birch (Betula nana), and cottongrass (Eriophorum vaginatum). We manipulated snow depth with a 60-m long fence erected perpendicular to the prevailing winds, and air/soil temperature with passive open-top chambers (OTC). Additionally, samples of leaf tissue were collected from landscape positions with different temperature regimes, and along a gradient of increasing temperature from north to south. Samples were analyzed for total N, neutral and acid detergent fiber, and lignin and cutin content.
Results/Conclusions
Deep snow increased the leaf tissue N content of B. nanaand S. pulchracompared to ambient snow conditions suggesting greater protein content. Deep snow acts as important insulation, decoupling soil temperature from air temperature during winter and resulting in warmer soils, which promotes mineralization of organic N and increased N availability to plants and subsequently greater leaf N. Deep snow, however, had a minimal influence on variables related to tissue digestibility. Snow depth effects were only evident at the start of the growing season when snow depth clearly impacted the phenology of leaf production. Effects of experimental warming on leaf N were modest suggesting a small decrease in protein content, but warming reduced digestibility in B. nana, S. pulchra, and E. vaginatum. None of the species examined exhibited a significant trend in tissue N with latitude even though there is clear negative relationship between temperature and latitude. Consequently, anticipated warmer summers and snowier winters in the Arctic potentially have opposite effects on forage quality for caribou.