Comparative responses of spiders and plants to maritime heathland restoration

Assessment of habitat restoration often rely on single-taxa approach, plants being widely used. Arthropods might yet complement such evaluation, especially in hard, poorly-diversified environments such as maritime clifftops. In this study we compared the responses of spiders and plants (both at species and assemblage levels) to increasing time of heathland restoration. Sampling took place in different sites of Brittany (Western France), using a replicated design of both pitfall traps and phytosociological relevés. A total of 5056 spiders belonging to 160 species, and 103 plant species were found. No change in species richness between degradation states was found for spiders. Plant species richness was lower in highly degraded habitats of recently restored sites but was not in the oldest restored one. Species composition greatly changed through turnover mechanisms between all sites and degradation states, for both spider and vegetation. Heterogeneity was higher in references states, and increased over restoration time between sites. The number of indicator species decreased with restoration age for spiders, while no indicator species was found for plants. Restoration is still on-going after 15 years, with no recovery of reference assemblages for both plants and spiders, but there were some signals toward reference in the oldest restoration site. Plants and spiders were proved to be complementary bio-indicators of post disturbance restoration, as they bring different, scale-dependent information on restoration success.