Using functional traits and species diversity to evaluate restoration success of coastal dunes

Abstract

Questions Evaluating reasons for the success (or failure) of restoration projects is one of the major goals for applied ecologists in the context of the dramatic worldwide decline in biodiversity. To that end, finding appropriate indicators and reference ecosystems is mandatory, especially for habitats in which restoration projects have been barely evaluated over the long term, such as coastal sand dunes. Do different indicators provide complementary information to evaluate restoration success? How successful is sand dune restoration after 30 years? Location Brittany (France). Methods We report changes in the plant community over a period of 30 years following restoration using trampling protection and marram grass (Ammophila arenaria) planting in four sites that were highly degraded by sand extraction and over‐frequentation. We used several indicator types (geomorphological, taxonomic, functional) at different spatial scales (alpha, beta, gamma) to assess recovery since restoration in four sites of the northern coast of Brittany and undertook comparison with reference sites. Results Our results indicate that over the 30 years after restoration the gamma richness of typical species and overall vegetation conservation status increased. We also found that restoration induces the recovery of zonation in plant communities, which become organized along the typical sea–inland gradient. We showed that use of functional traits and diversity indices is effective to compare restored communities with reference data from the literature. Based on this approach, we demonstrated that, according to most functional indicators, restored communities converge over time with the patterns found in reference data. Conclusions We demonstrated that restoration of coastal dunes after 30 years induced the recovery of sand accumulation, typical species cover, sea–inland plant community zonation and community functional characteristics. Despite these positive results, which indicated overall success and confirmed interest in such restoration projects, we found an important discrepancy in restoration success among study sites (e.g., level of recovery of typical species cover, functional diversity). Finally, our study confirms the interest of functional composition and functional diversity as restoration success metrics.

Reflecting on two and a half decades of restoration ecology in Applied Vegetation Science (1998–2023)

“…For example, Chollet et al. (2023) explored the occurrence of typical species, beta‐diversity and functional traits as indicators of restoration success in the absence of a suitable reference site. They argued that beta‐diversity and functional analyses are good indicators of success while acknowledging the difficulty of achieving the return of all typical species at their study sites—echoing ideas presented in 1998.…”