Herb layer in silver fir – beech forests in the western Pyrenees: Does management affect species diversity?

Silver fir-beech forests form ecologically important ecosystems in European mountains, where they have been intensively managed due to timber harvesting. Forest management effects can be evaluated using herb layer diversity as an indicator of environmental changes. Therefore, revealing the patterns of herb layer diversity is necessary for developing strategies for sustainable management. Knowledge on management history of fir-beech forests in the western Pyrenees is still limited. In this study we aim to disentangle the environmental drivers of species richness and species composition of these forests emphasizing the role of forest management. We sampled the herb layer vascular plants in 68 plots distributed among 14 silver fir-beech stands of the association Scillo lilio-hyacinthi-Fagetum sylvaticae and related diversity patterns with management histories, light conditions and topographic and climatic variables. Four management categories were established: recently managed, long managed, recently abandoned and long abandoned. Species richness was analysed by GLMM and species composition by partial CCA and PCNM. Multivariate dispersion analysis was used to assess differences in beta diversity among management categories. Management, continentality and slope had in general a weak effect on species richness, continentality with a positive effect whilst slope and management, in category of recently abandoned stands, with a negative effect. In addition, the percentage of large gaps had a moderate effect on open area species richness. Species composition was related to slope, ombrothermic index, forest management and spatial effects in terms of neutral processes. Long managed forests showed differences in beta diversity with recently abandoned and long abandoned forests. Our study suggests that environmental variables in combination with spatial effects are the main drivers of species diversity at small sampling scale, highlighting that management plays an important role in these western Pyrenean silver fir-beech forests.