Terrestrial arthropods as indicators of restoration success in an active limestone quarry

Limestone quarries are industrial sites that impact natural areas, thus their restoration is crucial for mitigating these impacts and reducing biodiversity loss. Restoration can be achieved through active management projects, such as hydroseeding and soil amelioration. Our study aims to evaluate the results of an active restoration project performed at a limestone quarry in Piedmont (NW Italy) using terrestrial arthropods as ecological indicators. We sampled four areas of the quarry restored in different periods between 1999 and 2016, following the quarry development, and showing different stages of vegetation succession, from sparse grassy vegetation to woodland. Additionally, we included a semi-natural xerothermic grassland outside the quarry as a control area. Arthropods were sampled at 20 points (four for each successional stage, and four at the control site), each consisting of three pitfall traps, filled with 100 ml of 20% propylene glycol as preservative liquid and spaced about 3 metres apart. All traps had been activated for seven days each month, from May to October 2024, for a total of five sampling sessions. Overall, we collected 13164 individuals belonging to 107 families. RDAs and GLMMs were applied to test for differences in community composition and biodiversity indices according to the restoration stage, and between the quarry and the control area. RDAs showed that the community composition was mostly similar at the different restoration stages and in the control area. Some coprophagous beetle families, such as Scarabeidae and Geotrupidae, were associated with the semi-natural xerothermic grassland, while predators such as Carabidae and several spider families were associated to the earlier successional stages created by the quarrying activity. GLMMs revealed a higher arthropod diversity in the oldest successional stage, now colonized by broadleaved woodlands. On the other hand, species richness reached a higher value in the control area, outside the quarry. These results suggest that predator arthropods can thrive in restored quarries, leveraging on sparse grassy vegetation in the newly restored areas of the quarry. On the contrary, coprophagous and necrophagous beetles are more abundant outside the quarry. Notably, high arthropod diversity in the oldest part of the quarry suggests that active restoration management is a profitable tool for restoring these post-industrial sites and achieving biodiversity conservation targets.