Human recreation shapes the local scale impact of ungulates on the carbon pools of a temperate coniferous forest

Greenhouse gases accumulation constitutes one of the main problems of modern society. Forests, which are a main terrestrial carbon sink, could represent a great help to reduce carbon footprints. Recent studies show that animals play a big role in carbon dynamics, and while the impacts of animals such as ungulates are affected by human presence, these effects have not been considered in studies on carbon stocks. Here, we studied the impact of ungulates on different carbon pools of a temperate coniferous forest at the Veluwe area (Gelderland, the Netherlands), and incorporated the influence of humans on ungulates presence and vigilance at fine spatial scales. We selected 22 paired plots at 20 and 100 m distance from human trails, ensuring that all of them had comparable environmental conditions. We divided each plot in three subplots, and in each subplot, we collected a sample of aboveground vegetation, understory litter and soil. Using camera traps in the same plots, we related differences in presence and behaviour of ungulates with the above-mentioned carbon stocks measured in the same plots. We found consistently fewer ungulate visits per day at 20 m than at 100 m from human trails, while their vigilant level was not significantly different. The concentrations of carbon were substantially higher in all three measured carbon pools at 20 m than at 100 m distance from the human trails. Hence, our study suggests that ungulates not only have an impact on the carbon stocks of temperate forests, but moreover that this impact is affected by human presence through the proximity to human trails. We suggest that for a proper understanding of carbon dynamics in forests, not only the impact of animals should be considered, but also how this impact is influenced by human activities.