Landscape structure influences browsing on a keystone tree species in conservation areas

Abstract

Aspen is a keystone species in boreal forests. The future of aspen in many conservation areas is threatened by ungulate browsing. Our aim was to study the effect of browsing on aspen regeneration and population structure in conservation areas in Central Finland, and the effect of surrounding landscape structure on browsing. Aspen density varied greatly among and within conservation areas. In about half of the conservation areas, middle-sized aspens were scarce or missing, which indicates heavy browsing in the recent past. In addition, the number of dead, large aspens in advanced decay stages were rare. Browsing pressure varied greatly among the areas, but on average, a bit more than half of the living aspens had been browsed. Landscape structure influenced browsing so that increasing proportion of farmland within 1 km and 3 km of the conservation areas decreased browsing pressure. The poor recruitment of aspen in many conservation areas jeopardizes the accumulation of large living and dead aspens. This means that many aspen-associated threatened species are in the risk of local extinction, unless aspen recruitment is enhanced by management.