Outdoor recreation in protected areas affects animal-mediated seed dispersal

Outdoor recreational activities increase human pressures on natural ecosystems, including protected areas. This may adversely impact not only species abundance, but also their associated ecosystem services. We investigated the effects of outdoor recreation on seed dispersal, a critical service primarily provided by birds and mammals in temperate regions. We examined the effects of outdoor recreation on the diversity and composition of bilberry (Vaccinium myrtillus) dispersers in Tatra National Park (Poland), an alpine protected area visited by millions of tourists yearly. We established transects in public-use and restricted areas to systematically collect all bird and carnivore feces containing bilberry seeds. We estimated the number of seeds contained in each feces, identifying bird species through DNA barcoding and mammals via visual field assignment. Frugivores dispersed almost 20 times fewer bilberry seeds per m2 in public-use than in restricted areas. Outdoor recreation did not strongly influence the diversity of bilberry dispersers, but affected the community composition, with different species dispersing seeds in public-use and restricted areas. Our results additionally suggest that the quantitatively most important disperser species, primarily brown bears Ursus arctos, avoided public-use areas, which explains the large differences found in the quantity of seeds dispersed. This study indicates that outdoor recreation can negatively affect animal-mediated seed dispersal in protected areas, potentially affecting plant community dynamics and ecosystem functioning. Management strategies such as closing areas to people and controlling the number of visitors may be effective in ensuring that human activities do not disrupt vital ecosystem services in heavily visited protected areas.