Stand maturity affects positively ground-dwelling arthropods in a protected beech forest

Context: Sustainable forest management is a widely held international goal and more knowledge is needed on invertebrate assemblages, essential to the ecological functioning of forest ecosystems. Aims: We aim at evaluating the effects of microsite conditions on spider, centipede and ground beetle assemblages living in an unmanaged protected beech forest within the Natural Park of Alpi Marittime (SW-Alps, Italy). In view of our results, we provide insights on the successional pathways of the focal assemblages in relation to future management of the forest, recommended by the local authorities for conservation purposes. Methods: We placed 50 pitfall traps along four transects crossing the forest and emptied them monthly, from July to October 2011. We characterized the four arthropod assemblages in terms of abundance, species richness, diversity and biomass and related them to leaf cover, rock cover, wood debris cover, litter depth, number of trees, mean tree size and light conditions at ground level using generalized linear mixed models (GLMM) and canonical correspondence analysis (CCA). Results: Thirty-one species of spiders (1,212 individuals), twelve of centipedes (262 individuals) and eleven of ground beetles (2,177 individuals) were collected. In all groups, matureforest species highly dominated the samples. Tree size proved to be one of the most important parameters conditioning the assemblages, in particular spiders and ground beetles. A minor effect of light conditions and ground cover (presence of wood debris) was also detected. Conclusions: In view of our results, the recent guidelines for the management of the forest seem in accordance with an effective conservation of the forest arthropod assemblages. Interventions aimed at stabilizing and renovating critical areas within the forest go along with a progressive amelioration of the forest arthropod community. With respect to the maintenance of a large degree of arthropod diversity, stand thinning may not be the most effective management, and reaching a more mature stage might be of interest.