Reindeer use of low Arctic tundra correlates with landscape structure

Abstract:

Rapid climate change in Arctic regions is linked to the expansion of woody taxa (shrubification), and an increase in biomass as tundra becomes greener. Reindeer and caribou (Rangifer tarandus) are considered able to suppress greening through grazing and trampling. Quantifying use of different vegetation types at the landscape scale can help us understand reindeer impact on the growth of deciduous shrubs, many of which serve as fodder (e.g. Salix spp.), and shrub recruitment in favourable habitats, such as naturally denuded landslides in permafrost areas. Understanding the spatial distribution /structure of reindeer pressure on vegetation is important to project future patterns of greening, albedo, snow capture, active layer development, and the overall resilience of tundra rangelands under ongoing climate change. Here we quantify reindeer habitat use within the low Arctic tundra zone of Yamal, West Siberia estimated from pellet-group counts. Our results confirm intensive feeding by reindeer on terrain with high normalized difference vegetation index, steeper slopes and ridges and upper slopes, and a preference for low erect shrub tundra. These areas were primarily ridges and shoulders providing insect relief during summer due to their wind exposure relative to concavities. Concave areas (e.g. old landslides) with tall Salix thickets were used less by reindeer. Low-use of tall Salix habitats indicated that reindeer are unlikely to suppress the growth of already tall-erect woody taxa, while they exert maximum pressure in areas where shrubs are already low in stature, e.g. ridgetops. Reindeer ability to suppress the regrowth and expansion of woody taxa in landslide areas seems limited, as these types were less used. Our results support the hypothesis that reindeer may mediate climate feedbacks, such as albedo, through their preferential use of areas with high nutritious quality, as these have a shallower active layer compared to sites less used by the reindeer.