Balancing forage and fear: How people, environment and predators shape reindeer grazing in the Fennoscandian tundra

The long history of reindeer herding in Fennoscandia has shaped the mountain tundra by influencing its productivity, nutrient and carbon cycling and vegetation structure. By partly limiting shrub expansion, extensive reindeer grazing contributes to ecosystem resilience and helps mitigate climate change effects.

Yet, outdoor tourism is discussed as a major pressure that can alter reindeer grazing patterns, with likely consequences cascading onto the tundra plant communities and vegetation structure. To study this, we tagged reindeer with GPS and accelerometers in three Swedish reindeer herding districts experiencing different levels of tourism pressure, and analysed their occurrence and grazing activity in relation to human infrastructures, habitat and predators.

In the district with the highest tourism pressure, reindeer avoided large buildings but tolerated hiking trails. Responses were more mixed in the two other districts where large national hiking trails were avoided, but small cabins were not. Interestingly, the reindeer grazing patterns measured with accelerometers showed a different response to that inferred from reindeer occurrence alone, revealing that even where reindeer did not avoid human infrastructures, their grazing activity was still decreased.

In all districts, we detected interactive effects between predators and human infrastructures, suggesting a ‘human‐shield’ effect at play, that is reindeer used the proximity to specific types of human infrastructure as a refuge from predation. This context‐dependent tolerance of reindeer towards humans according to predator presence reveals that even non‐lethal human presence in the mountains, in the form of tourism, can influence predator–prey interactions in the tundra.

By decoupling spatially explicit grazing activities from presence‐only habitat selection, this study highlights that, even if reindeer might appear tolerant to human presence in the mountains, outdoor tourism can still disturb them by disrupting their grazing. As this study was conducted in a region experiencing substantial land use changes, our findings stress the need to better recognise the effects of human interactions with the tundra wildlife, particularly herbivores such as reindeer, as these can cascade onto other trophic levels and therefore affect broader ecosystem processes under climate change.