Soil unsealing in Mediterranean schoolyards: what factors drive ant communities?

Abstract

Soil unsealing, the process of removing the impermeable top layer of soil, is increasingly advocated by urban planning policies. The role of unsealed areas in biodiversity conservation, particularly soil biodiversity, remains strongly understudied and especially in understanding the recolonization dynamics of soil biodiversity in these new habitats. Besides, the various types of soil cover resulting from soil unsealing could potentially influence the recolonization kinetics. This study focused on 79 unsealed plots located in 14 schoolyards along the French Mediterranean coast, investigating ant communities through the placement of 485 baits on unsealed plots. Two variables were considered: the duration since soil unsealing (1 or 2 years) and the type of soil cover (wood chips, plantations mulched with wood chips or lawns). Remarkably, these unsealed areas act as habitats for ants from their very first years of creation: a rich number of ant species (21 species; a fifth of the regional pool and 10% of the metropolitan French species) has been observed. Additionally, notable changes in ant communities were evident within a single year: plots unsealed for 2 years exhibited significantly higher indices of ant abundance and species richness compared to those unsealed for 1 year. However, the construction of these spaces influences the present communities, with wood chip-covered areas significantly less rich and abundant in ants compared to other ground cover types. These findings represent a promising starting point and offer insights into the potential of such projects for soil biodiversity conservation.