Spatial tree community structure in three stands across a forest succession gradient in northern boreal Fennoscandia

Development of species composition during succession is well studied in natural boreal forests, but empirical assessments of how within-stand spatial structure develops in late-successional stages arefew . Here, wequantifiedspatialpatternsinthreeunmanagedstandsconsistingofPicea abies (L.) Karst. and Betula pubescens Ehrh. and Betula pendula Roth (hereafter Betula spp.) in northern boreal Fennoscandia. We conducted a comprehensive analysis of small-scale spatial point patterns in three fully mapped 1.2-ha sample plots, representing different forest developmental stages: mid-successional, late-successional and old-growth forest. We used several variants of Ripley's K-function to analyze the spatial point patterns along the successional gradient. Univariate analyses showed that mature trees of both species were either randomly distributed or clumped. P. abies saplings were clumped, and Betula spp. saplings occurred in a random or clumped manner. In the bivariate analyses, saplings were more likely to be found in the surroundings of mature trees of the same species, but occurred independent of the individuals of other tree species. Mature treesshowedinterspecificrepulsion. Onlymodestdif ferencesoccurredintheunivariatepatterns between the three successional stages, but in the bivariate analyses the most evident patterns, i.e.intra specificattractionandinterspecificrepulsion, werestrongerintheoldersuccessional stages.Overall, thestudiedstandsappearstructuredasspecies-specificmosaics. Thesemosaics, along with mixed species composition, seem to be maintained by species self-replacement, which contrastswithfindingsfromearlierstudies.