Data from: Greater biomass from Arctic greening absorbs increased grazing pressure from a large herbivore

Arctic warming is causing widespread “greening” of tundra ecosystems. What
this means for plant-herbivore relations, including the grazing pressure
herbivores exert on increasingly productive tundra ecosystems, is poorly
understood. Svalbard is one of the fastest warming places on Earth, with
concomitant increases in both forage biomass and reindeer numbers. In 11
years between 1998 and 2023, we measured grass biomass and the proportion
of shoots grazed in mesic grass-dominated tundra to evaluate whether
increased forage biomass of grass absorbed the grazing pressure of more
reindeer. Also, we used GPS data from adult female reindeer (2009-2023) to
identify if grazing pressure was relieved by spillover into other
habitats. During the study period, reindeer abundance, estimated by annual
capture-mark-recapture, tripled, while grass biomass only doubled. Grazing
pressure increased from 4% to 8%, which was lower than expected from the
increased reindeer density. This discrepancy was not caused by spillover
into other habitats, but rather by increased grazing in higher-biomass
patches that have emerged with summer warming. Our findings support the
notion that increased summer forage has contributed to Svalbard reindeer
population growth, notably by making available higher biomass grass swards
that allow for greater food offtake.