Does forest age affect soil biodiversity? Case study of land snails in Mediterranean secondary forest

Based on a sampling design used for vascular plants, the effect of forest age (i.e. the time in years since a land patch became a real forest patch as a measure of temporal continuity of forest characteristics) on land snail richness, abundance and composition was assessed in 18 plots in Mediterranean evergreen and deciduous oak forests, belonging to four Sites of Community Importance in Italy. Most examined plots belong to young forests; in particular, three age classes were considered (class 1, <22 years; class 3, 38–56 years; class 5, >77 years). Twenty-seven species and 2433 individuals were recorded. Box plots showed that forest age did not seem to be a key factor for land snail species richness and abundance at least in the time range of examined forests. However, this may not be true, if real old-growth forests are considered. No differences between evergreen and deciduous forest were found too. With regard to species composition, Non-metric multidimensional scaling demonstrated an assemblage of species widespread in all forest age classes, while Indicator Species Analysis failed to identify any species as indicator for any age category. This shows that a process is underway but has had insufficient time to differentiate assemblages and to accumulate the majority of rare species, due to the young nature of examined forests. Habitat structure may affect communities more than forest age: suitable microhabitats (a few old/very old trees for shelter) are a sufficient prerequisite for land snail diversity, ensuring community survival and protection, irrespective of forest age class. These findings highlight the importance of habitat structural complexity at local scale for preserving invertebrate diversity in Mediterranean secondary forests.