Linkage of forest productivity to tree diversity under two different bioclimatic regimes in Italy

We analyzed the Italian National Forest Inventory data set to evaluate the interdependence of forest productivity, tree species richness (used to indicate biodiversity), climate, and soil factors. We tested the hypotheses that the relationship between biodiversity and forest productivity is positive and significant for all forests in Italy and whether the relationship is the same for forests growing in the temperate and Mediterranean bioclimatic domains (regions) of Italy. We used generalized additive models to explore the univariate response curves for the data and then performed structural equation modeling (SEM) and multi-group SEM analyses to evaluate the relationship between biodiversity and productivity. We found that the SEM model for the entire dataset explained about 60% of the variation in forest productivity. In addition, the variation associated with species richness was greater than variation due to climatic factors and the variation in climate factors was greater than the variation in soil factors (all relative to their contributions to productivity). The multi-group SEM showed a more predominant effect of biodiversity and climate on productivity in Mediterranean compared to temperate forests. In both cases, we observed a moderate effect of soil (factors) on forest productivity. Our results support the hypothesis that increasing tree diversity in forests could help reduce the effects of climate warming and enhance ecosystem productivity in the Mediterranean region.