Spatial patterns of ground vegetation, soil microbial biomass and activity in a mixed spruce‐birch stand

Abstract

Trees directly and indirectly influence the above‐ and below‐ground environment, and can be expected to modify the spatial patterns of organisms associated with the forest floor. This study aimed to examine the effects of a coniferous (Picea abies) and a broad‐leaved (Betula pubescens) tree species on the spatial pattern of ground vegetation and soil microbial properties in a mixed stand in central Sweden. I have characterised the species composition of ground vegetation, soil microbial biomass and activity, photosynthetic active radiation (PAR), soil water content and soil pH in the stand, and tested whether the spatial patterns of these variables were related to the positioning of trees. Geostatistics were used to describe the spatial variation in ground vegetation, soil mirobiological properties and the soil surface environment. PAR, soil water content and the cover of the moss Brachytecium reflexum and associated herb species decreased with the influence of spruce trees. Microbial biomass, measured as the amount of phospholipid fatty acids, decreased with spruce influence but increased with the influence of birch trees. Microbial respiration was not affected by spruce but increased with the influence of birch. Ground vegetation and microbial respiration, which were influenced by one tree species only, aggregate on a scale of 4‐5 m, corresponding fairly well with patches of a single tree species. Soil microbial biomass, which was affected by both tree species, aggregated on a scale of 7‐8 m. roughly corresponding to the distance between patches of spruce and birch trees respectively. I suggest that spruce trees influenced vegetation mainly through shading, and that a difference in the availability of organic matter under birch and spruce trees caused spatial variation in microbial biomass and activity. Thus, spatial patterns in ground vegetation and soil microbial properties may develop in a mixed forest of coniferous‐broad leaved trees, as a result of the difference in influence of tree species and nested variation associated with the arrangement of the trees.