Concordance between plant species, oribatid mites and soil in a Mediterranean stone pine forest

Biological interactions between above-ground and below-ground organisms are not clearly defined among communities with regard to compositional patterns. The study investigates the concordance of species assemblages between vascular plants and oribatid mites and soil chemical properties with special attention to the role of vegetation structure, i.e. tree, shrub and herbaceous cover, for biological components. Data were collected in a Mediterranean coastal Nature Reserve using sampling design based on random selection of plots with cover of stone pine (Pinus pinea L.) exceeding 15%. Agreement of distribution patterns was verified by Spearman's rank correlation coefficient applied to pairs of matrices of plot scores by principal component analysis (plants, mites and soil) and the Mantel test. The feasible role of vegetation cover on plant and mite assemblages was tested by redundancy analysis (RDA). Significant correlations were found for biological assemblages, indicating congruent plant-mite compositional patterns. On the other hand, the hypothesis of concordance between biological communities and soil was rejected. Moreover, RDA showed that vegetation cover was a driver of both plant and oribatid mite assemblages. In particular, herbaceous cover proved to be a good proxy for the two biological communities investigated, with different taxa linked to forest clearings and to areas with denser tree cover. Our results indicate that soil features were not of primary importance for below-ground and above-ground community assemblages in the study area. In the light of our findings and ongoing threats in coastal areas, we recommend that management measures be directed at maintenance of diversified vegetation structure, which may ensure above-ground and below-ground biodiversity with diverse biological community assemblages.