Diversity of saproxylic beetle communities in chestnut agroforestry systems

Abstract

Chestnut (Castanea sativa Mill.) has been exploited over the centuries for different uses. Nowadays, chestnut is mostly managed as coppice or orchard, creating a matrix of different forest structures. In particular, saproxylic species may provide information to correlate forest naturalness with stand structure. In this study, we evaluated how different management methods might influence the diversity of beetles hosted in chestnut agroforestry systems. Three management options were considered: young and mature coppice stands, and the traditional fruit orchard. Microhabitats occurring on veteran trees were also surveyed to investigate their effect on saproxylic communities, in the fruit orchard. The study area is located in Southern Italy, Aspromonte National Park, where Coleoptera were collected using window flight traps and the stand structural traits were also quantified. In the fruit orchard, a census of the occurring microhabitats was also realized. We used the following diversity indeces (α-diversity) to assess the state of conservation of the analysed forests: (i) Shannon Index; (ii) Margalef’s Richness index; (iii) Equitability index; (iv) Dominance index. Results revealed that forest management have a fundamental role in influencing the diversity of Coleoptera communities and saproxylic beetles. A lower species richness was observed in the mature coppice in comparison with the young coppice and fruit orchard. Nevertheless, these agroforestry systems, reflecting differentiated structural traits, allowed the development of highly specialized and threatened species (34.3% included in IUCN risk categories), with important contribution to conservation of biodiversity in the rural landscape. Finally, the abundance and diversity of microhabitats in the traditional fruit orchard had positive effects on many saproxylic beetle families. These beetle communities, particularly saproxylic species, can be used as excellent bioindicators in actively managed agroforestry systems, suggesting sustainable forest management options for chestnut, while the conservation of veteran trees rich in microhabitats can be considered fundamental for preserving many endangered insects.