Riparian vegetation ecology : an observational study into the effects of forest management on understory vegetation communities along boreal headwaters

Abstract: Riparian forests along headwater streams have long been recognized for their role as an interface between the terrestrial and aquatic ecosystem. The over- and understory vegetation performs essential ecological and biochemical functions, which are important for stream functions. Headwaters and their riparian forests have historically long been overlooked in Swedish forest management, leading to clearcutting up to the stream’s edge. Previous research found that the forest structure in production forests was significantly different from primary forests. This thesis focused on the possible effects of forest management on the understory vegetation communities. I inventoried 7 production forests along a management gradient and compared their vegetation communities to 5 primary forests in forest reserves. In all forests a vegetation survey was conducted using 12 quadrates of 1x1m arranged in 6 transects. Vegetation communities were compared for species diversity, community composition and the environmental characteristics. My results showed that forest type (production, reserve) did not significantly affect species diversity, although I did find that diversity related differently to forest age based on forest type. The community compositions were found to be different between the two forest types, although significant overlap has to be noted. Finally, light availability, as a function of canopy openness was found to be an important driver behind the vegetation communities. Earlier findings on canopy openness between the forest types were repeated with canopy openness being marginally, but significantly higher in the forest reserves. Generally, this thesis showed that production forests contain large variation between different sites along a management gradient. Within this variation, production forests can house similar or larger number of species and are enormously relevant for the preservation of biodiversity. Therefore, management in the riparian zone may have important implications for the understory vegetation and by extend riparian functioning.