Slope aspect modifies community responses to clear-cutting in boreal forests. Abstract. Slope aspect modifies microclimate and influences ecological processes and spatial distribution of species across forest landscapes, but the impact of slope aspect on community responses to disturbance is poorly understood. Such insight is necessary to understand landscape community dynamics and resilience. We compared bryophyte (liverworts and mosses) communities in matched 0.02-ha plots of four boreal stand types in central Sweden: recently clear-felled and mature stands dominated by Norway spruce in southfacing and north-facing slopes. Differences between forests and clear-cuts were interpreted as effects of clear-cutting, and differences between south-and north-facing slopes as effects of aspect. In response to clear-cutting, bryophyte cover and composition changed more in southfacing slopes. Only one out of ten significantly declining species in south-facing slopes also declined significantly in north-facing slopes. North-facing slopes lost fewer bryophyte species, and among those, fewer forest species and fewer species associated with wood and bark. In north-facing slopes, the average proportions of mosses and liverworts shared between the forest and the clear-cut plot were 88% and 74%, respectively. Corresponding numbers for south-facing slopes were 79% and 33%. In addition, more bryophyte species were added in north-than south-facing slopes after clear-cutting, somewhat reducing the difference in compositional change between aspects. South-and north-facing mature forests differed in species composition, mostly due to higher richness of mosses in south-facing slopes. The smaller changes in bryophyte communities on north-facing slopes in response to clear-cutting have implications for ecosystem dynamics and management as high local survival may enhance landscape-level resilience. Ecology

Question: The practice of extracting logging residues after clear-cutting for bioenergy purposes is spreading. Logging residues constitute a shelter in clear-cut areas and therefore concerns have been expressed that their removal could make the ground and its vegetation more exposed to extreme microclimatic conditions. We asked whether logging residues and forest edges can protect ground-dwelling forest bryophytes from fatal microclimate events following clear-cutting. Location: Boreal forests of central Sweden. Methods: Using transplants of eight forest floor bryophyte species we experimentally analysed the sheltering effect (less solar radiation and less wind) of logging residues and forest edges in seven clear-cut areas. Transplants were placed in two contrasting positions in each area; near a north-facing forest edge and in the centre of the clear-cut area. In each position, half of the transplants were covered by a layer of spruce branches and the other half was left uncovered. We estimated proportion of apparently living shoots (apparent vitality) and measured radial growth of transplants during one growing season. Results: Position in the clear-cut area, but not cover of spruce branches, clearly influenced radial growth. Vitality scores were higher among transplants covered with branches and the lowest apparent vitality was observed in uncovered transplants in the middle of clear-cut areas. The change in area of apparently living shoots during the course of the experiment (growth minus mortality) was unaffected by branch cover close to the edge but positively affected in the centre of the clear-cut area. In general, the effect of branch cover on bryophytes was higher in the centre of clear-cut areas. Here, climatic measurements showed that branch cover buffers during periods of extreme microclimates. Conclusions: Extraction of logging residues after clear-felling may reduce the survival of some ground-dwelling forest organisms. The additional sheltering provided by branches was unimportant close to forest edges. We suggest smaller clear-cut areas, green-tree retention and other ways to make logged areas shadier and less windy to mitigate the reduced shelter caused by harvest of logging residues.

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Summary1. 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. nonexperimental) slash harvest on species composition and richness of liverworts, mosses and vascular plants. The results call for modification of commercial slash harvest practices. 2. 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. 3. 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. 4. 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. 5. 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. 6. 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.