Evaluating partial cutting in broadleaved temperate forest under strong experimental control: Short-term effects on herbaceous plants

Abstract

Partial harvesting of forest for biofuel and other products may be less harmful to biodiversity than clear-cutting, and may even be beneficial for some species or groups of organisms such as herbs. There are, however, few well-controlled experiments evaluating positive and negative effects, such as species losses directly after harvest. In closed canopy mixed oak forest in Sweden, about 25% of the tree basal area and 50–90% of the understory was removed (mainly spruce, birch, aspen, lime, rowan and hazel). In each of six forests, we studied herbs in an experimental (cutting) plot and a control plot (undisturbed) before, and in the first summer, after the harvest (conducted in winter). Losses of species were similar in experimental and control plots (15–16%). The harvest increased species richness by 4–31% (mean 18%); also species diversity ( H′) increased. Several ruderals increased in experimental plots, but most changes occurred in grassland and forest species; partial cutting led to complex, partly unpredictable early changes in the herb community. A review of early effects of partial cutting (eight experiments) indicated that it increases herb species richness in stands of broadleaves, but apparently not in conifer stands; there was no evidence that partial cutting increases species losses. Thus, with respect to early changes after harvest, we found no negative effects of partial cutting on herbs. We suggest, however, that some proportion of closed-canopy mixed oak forest should not be harvested, to protect rare, potentially sensitive herbs, and to create stand diversity.