Community structure, diversity and spatial organization of enchytraeids in Mediterranean urban holm oak stands

• Enchytraeids of urban Quercus ilex stands vary in diversity, biomass and patchiness.
• Species richness seems to mainly increase with environmental heterogeneity.
• Species richness in Mediterranean cities is not lower than in cities further north.
• Some species show robust aggregation patterns, others do not.
• A high intensity sampling obviates to the low densities of Mediterranean assemblages.

There is a strong northern bias in Europe as regards enchytraeid community ecology, particularly in urban settings. We approached the enchytraeid assemblages of urban holm oak stands in Naples and Siena adopting a high intensity sampling that, for the first time in the Mediterranean climate zone, would ensure that the data collected be representative of the target populations. Structural parameters (diversity and evenness, biomass, size classes, aggregation) were compared across different spatial (regional, urban district, within habitat) and temporal scales (season and year). Species richness was found to change significantly only at regional scale; background data suggest that this may depend on the higher environmental heterogeneity occurring at Naples. Differences in size class structure were significant only on a seasonal scale and within either city separately. With one exception (Fridericia bulbosa s.s.), the patterns of spatial aggregation of the common species were fairly robust and the total range of patchiness was consistent with previous studies, despite the different sampling methodologies. The size of the sampling unit, the number of replicates per plot and the number of plots proposed in this study appear suitable to obviate the difficulties of evaluating Mediterranean enchytraeid communities.