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 south-facing 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 south-facing 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.