Red foxes enhance long‐term tree growth near the Arctic treeline

Recent climate warming is expected to increase tree growth and productivity, substantially altering ecological function and boundaries in northern ecosystems. Although climate largely determines the range and growth of trees in any biome, variations in microsite conditions can influence growth on a finer scale. Red foxes (Vulpes vulpes) are found in most terrestrial ecosystems and are considered ecosystem engineers through their denning activities. Added soil nutrients from prey remains, feces, and urine could benefit tree growth on dens in subarctic regions by alleviating soil nutrient limitations. We examined growth in white spruce (Picea glauca) trees growing on eight red fox dens and paired control sites at the Arctic treeline. Radial growth was 55% higher for trees on dens than on control sites between 1897 and 2017, despite similarities in tree ages and densities. This enhanced growth was more pronounced in younger trees, consistent with the decrease in growth with age among all trees. By promoting tree growth near the treeline, red foxes may act as hotspots for tree reproduction. Although the impacts on tree growth largely depend on the spatial distribution of dens, predators can create distinct microhabitats across the landscape, leading to increased vegetation productivity, persisting over many decades.