Tree diversity and ecosystem functions in mixed broadleaved forests of Central Italy (Tuscany)

The FunDivEUROPE project was aimed to study the role of tree diversity in ecosystem functions in European forests along a latitudinal-ecological gradient from Mediterranean to boreal forests. Within the explorative platform of the project, 36 (30x30 m wide) plots having different levels of tree diversity (i.e. species richness and species composition) were selected in Tuscany (Colline Metallifere). The focal tree species were Quercus ilex, Quercus cerris, Quercus petraea, Ostrya carpinifolia and Castanea sativa. In each plot were measured several variables related to ecosystem functioning, included soil properties (mineral components, microbial activity, roots), water budget, litterfall and element cycling, ground vegetation and tree regeneration, tree growth, foliar analysis (physiological and chemical characteristics), and insects and pathogens attack. This presentation reports some of the most relevant evidences in relation to tree diversity and ecosystem functions. (1) Leaf area index was positively related to diversity, thanks to a better exploitation of the canopy space in mixed forests. (2) Tree diversity reduced defoliation on C. sativa, as consequence of decreased of Dryocosmus kuriphilus attacks on chestnut tree crowns. This behaviour is to be connected to the mixture with oak species that houses cynipid galls and associated parasitoids. (3) The water use efficiency in deciduous oaks was affected by species-specific interactions. (4) Photosynthetic efficiency (measured by means of chlorophyll fluorescence a analysis) increased in Quercus cerris with the increase of species richness, but decreased in Quercus ilex in the same conditions. Concerning the understory vegetation, neither taxonomic nor functional target tree species diversity affected understorey species richness and diversity. Also, there was a lower species compositional differentiation between plots with higher tree species richness. However, functional dispersion between target tree species positively influenced understorey biomass. These results are discussed in terms of competition/ facilitation between different tree species in relation to their ability to exploit ecological resources. The outcomes for forest management is also discussed.