Reinforcement capacity of potential buffer zones: Forest structure and conservation values around forest reserves in southern Sweden

Buffer zones may reinforce protected areas and are often recommended, but have rarely been systematically studied in temperate forests. Globally, temperate broadleaved forest is considered to be the most disturbed biome, with small, scattered natural fragments. In theory, it is often assumed that nature reserves have heavily exploited surroundings. We tested this assumption using a random sample of 49 small reserves (forest area 5-225 ha) that lacked buffer zones. We expected two major outcomes: either a sharp decline in conservation value from the forest reserves to the surroundings, or a gradient of decreasing value from the reserves and outwards. Basic structural indicators of red-listed forest species were studied in the reserves, in their potential buffers (200 m wide), and in non-protected forests outside the buffers. On average, southern broadleaved deciduous forest covered 37% of the forested area in the reserves, 18% in the potential buffers and 5% in non-protected forest outside the buffers. The density of large living trees (>40 cm diameter at breast height, dbh) was 30 stems per woodland hectare in the reserves, decreasing to 15 in the buffers, and to 10 outside the buffers. Similar, but less marked gradients, were found for dead standing trees and downed dead wood. The diversity of trees and shrubs indicated relatively high conservation values in the buffers. Valuable reserves had valuable potential buffers, as conservation values of the reserves were positively correlated with those of the buffers. Our results show that heavy exploitation of surroundings cannot a priori be assumed for nature reserves. The results are encouraging for preservation of temperate forest biodiversity, since small reserves seem to be reinforced by their surroundings, but we suggest that protection by law or by other means is necessary to maintain the conservation values of potential buffer zones for the future.