To what extent do forest herbs recover after clearcutting in beech forest?

We studied the occurrence of 22 plant functional groups and the distribution patterns of 12 forest herbs in four clear-felled areas of different ages, and across ecotones between the forest and clearcuts in a 4383 ha beech forest in central Belgium. The main goal was to improve our knowledge on the clearcut harvesting system and its possible influence on herb vegetation. Within each study site, the herbaceous vegetation was sampled along a north-south and an east-west transect with points at 20 or at 10 m intervals. We studied a total of 82 vegetation relevés (4 m2) on 18 transects according to the Braun-Blanquet method. Around the study sites, the abundance of each species present was noted according to a grid-map with cells of 50 m × 50 m, up to a distance of 150 m from the clearcut edges. Differences in species' cover percentage and frequency between the clearcuts and the surrounding matrix were tested. The colonisation rate for each species was calculated and possible effect of clearcut age on the plant composition was examined. Results of this study show that plant functional groups with a high conservation value, such as ancient-forest species, stress-tolerant species and autochorous species showed a progressive decrease in time after clearcutting. Most of the studied forest herbs had a lower frequency and/or cover in the clearcut areas than in the surrounding forest matrix. For some of these species, we found a progressive abundance decrease along a 150 m-gradient within the forest towards the clearcut (e.g. Dryopteris dilatata, Luzula pilosa, L. sylvatica, Oxalis acetosella). Others, such as Anemone nemorosa and Circaea lutetiana, are characterised by a regular cover in the forest which suddenly drops at the edge and sustains a very low level throughout the clearcut. If some forest herbs recover better than others, data collected so far indicate that most of the studied species are not able to recover such disturbed sites within a few years. We conclude that silvicultural systems should be adapted to the dispersal and recruitment limitations of forest herbs in order to enable their long-term conservation. To achieve this goal, management without large clear fellings and harvesting methods that never leave the ground completely bare are proposed as alternatives to the clearcutting system.