Effects of slash harvest on bryophytes and vascular plants in southern boreal forest clear-cuts.
Slash harvesting from forests to provide bioenergy reduces the amount of woody debris in the managed forest landscape and changes the physical and chemical environment in clear-cuts. We examined previously unstudied effects of commercial (i.e. non-experimental) slash harvest on species composition and richness of liverworts, mosses and vascular plants. The results call for modification of commercial slash harvest practices. Differences between conventionally harvested (i.e. slash left) and slash-harvested stands were investigated 5-10 years after clear-cutting through analysis of 28 paired stands, with one 0.1-ha plot divided into five 0.02-ha subplots in each stand. The study was conducted in south central Sweden. The forests in the area have been modified over several centuries by repeated extraction of timber, initially to supply the mining industry, and later the forest industry. The species composition of mosses and liverworts in 0.1-ha plots was significantly affected by slash harvest, whereas the composition of vascular plant species was not. The species richness of liverworts was significantly reduced by slash harvest in plots of both sizes, whereas moss richness was reduced only in 0.02-ha plots. The loss of liverwort species was largest, with approximately one-third of the species disappearing. The species richness of vascular plants was not significantly affected by slash harvest in either plot size. Slash harvest reduced species richness of forest bryophytes and of bryophytes typically growing on organic substrates in open habitats. Species richness of non-forest bryophytes on inorganic substrates remained unchanged. Synthesis and applications. Our results show that slash harvest reduces shelter and woody substrates, which changes species composition and reduces species richness of liverworts and mosses in clear-cuts. Increased mechanical disturbance that removes remnant vegetation and exposes mineral soil may also play a role. In order to conserve bryophytes, we advocate mitigation of adverse ecological effects through enhanced environmental care within slash-harvested stands. Leaving more tree clusters, and creating and protecting large woody debris would be especially important in these stands, and would also improve the habitat for other organisms.