Richness of forest specialist plant species increases with forest fragmentation per se but decreases with proximity to forest edge and reduced forest patch size

•1. Quantifying the effects of habitat fragmentation presents challenges due to the complexity of landscape-scale habitat configuration and its interaction with landscape and local processes. While patch-scale studies contribute valuable insights, extrapolating their findings to landscape scales is problematic due to the influence of landscape-scale processes.
•2. We used structural equation modelling to examine the direct and indirect effects of landscape-scale attributes around sampled forest patches including forest amount, edge density, number of patches, mean patch size, and mean interpatch distance, and patch- or plot-scale attributes including focal patch size, focal patch isolation, sample plot distance to forest edge, within-plot microhabitat heterogeneity, and plot soil pH, on species richness of woodland specialist plants in 16 sample plots within each of 97 British woodlands (‘focal patches’).
•3. We find direct positive effects on woodland specialist richness of: (i) forest edge density in the landscape, suggesting positive effects of fragmentation per se, (ii) distance to forest edge of the sample plot, suggesting negative local edge effects, (iii) focal patch area, (iv) within-plot heterogeneity and (v) within-plot soil pH. We also find indirect positive effects of: (i) forest amount in the landscape through its indirect correlations to focal patch size and distance to forest edge, and (ii) number of forest patches in the landscape, through its correlation with edge density in the landscape.
•4. Synthesis. Our results suggest positive effects of fragmentation per se, that is fragmentation controlling for forest amount, on richness of specialist forest plants, despite their negative local edge response. This confirms that cross-scale extrapolation is not valid in habitat fragmentation research: negative patch-scale edge effects do not scale up to produce negative landscape-scale fragmentation effects.