Linking forest dynamics to richness and assemblage of soil zoological groups and to soil mineralization processes

Abstract

We conducted a study in a spruce forest, grown on a sub-acidic bedrock, in the Italian Alps in order to assess whether (1) forest dynamics influences animal communities, and in particular whether the richness of zoological groups peaks during the regeneration phase, (2) the diversity of zoological groups is correlated to C mineralization, considered as a measurement of soil functioning, (3) aspect influences the above relationships. We compared soil animal communities, soil physico-chemical features and nutrient mineralization in three developmental phases of spruce, with increasing tree cover (clearing, regeneration and mature trees) and two sun exposures (North, South). Animal communities changed with spruce dynamics. Mature spruce stands were characterized by higher densities of Acari, while regeneration stands and clearings were mainly characterized by higher densities of Collembola and most groups of macrofauna. As hypothesized, the richness of zoological groups was highest in regeneration stands, especially in the south facing site, probably because of the simultaneous occurrence of a dense herbaceous cover and spruce litter, leading to higher local soil heterogeneity. However, zoological group diversity (Shannon index), which was lowest in mature stands, was better explained by the herbaceous cover, i.e., by the quality of food resources, in both south and north facing sites. Variations of soil characteristics with the developmental phase of trees, reflecting a higher litter input and slower litter decomposition rate beneath mature trees, are in line with the distribution of zoological groups. As expected, the diversity of zoological groups was positively correlated to C mineralization. Changes in animal communities with phases of the forest cycle were much more pronounced in the south compared to the north facing site. In light of previously published results, we discuss how the diversity and composition of soil animal communities are plant driven.