Key issues in Northwestern Mediterranean dry grassland restoration

Dry grasslands of the Northwestern Mediterranean Basin are seminatural species-rich ecosystems, composed of many annual species and some structuring perennial species. As these grasslands have been used as rangelands for centuries, human management (grazing; fire regimes) is one of their main ecological and evolutionary drivers, along with the Mediterranean climate. Despite EU conservation policy, damage to such grasslands still occurs and efficient ecological restoration is needed. This article reviews restoration constraints, effective techniques, and research perspectives for restoring them in the light of their ecological characteristics. Major restoration constraints specifically include (1) a poor contribution of the internal (seed bank) and external (seed rain) species pools, and (2) low establishment of some perennial species. The latter may be the result of the low seed quantity or quality of perennial species, stochastic or extended droughts, high soil nutrient content that may lead to competition (e.g. between weed and target species), inappropriate grazing management or fire regimes leading to shrub encroachment, or the death of target species seedlings in early stages of restoration. Successful restoration techniques include seeding, transplanting, hay transfer, and timely soil transfer, all of which have to be adapted to regional plant phenology and to local Mediterranean climate. They must be combined with appropriate grazing or fire management. Their success may depend on years with particular rainfall amounts or patterns or on particular target plant species. We discuss research perspectives contributing to a better understanding of seed dispersal, seedling recruitment, and soil processes and suggest the benefits of using ecosystem engineer species.

Automated summary

Dry grasslands of the Northwestern Mediterranean Basin are seminatural species-rich ecosystems, where human management and Mediterranean climate play a significant role. Restoration efforts must address constraints related to poor seed bank contribution, low establishment of some perennial species, and other factors like competition, grazing, and soil processes. Successful restoration techniques include seeding, transplanting, hay transfer, and timely soil transfer, adapted to local climate and plant phenology.