Seed bank as a source for the spontaneous regeneration of dry grasslands on former arable fields in an agro‐pastoral landscape

Introduction Dry grasslands have suffered significant losses due to overgrazing and conversion into croplands in Europe. Objectives This study investigates seed bank diversity and density along a succession gradient of abandoned crop fields in Transylvania, Romania, to assess the contribution of seed banks in spontaneous grassland regeneration. Methods We assessed seed bank composition and aboveground vegetation in young, medium‐aged, old‐abandoned arable fields, and old‐growth grasslands at three sites in the Transylvanian Basin. Results Analysis revealed a unimodal relationship between species richness of the seed bank and succession stage. This is attributed to the seed rain of establishing species at the ascending part of the curve, and to seed viability loss, litter accumulation over time, which prevents seed penetration into the soil, and a declining abundance of ruderal species at the descending part. Although seed bank richness was lower than that of the aboveground vegetation at the plot level, half of the species from the entire species pool were represented in the seed bank at the landscape level. Furthermore, our trait‐based analysis revealed that slow‐colonizing grassland specialists with a transient seed bank typically exhibit a lack of alternative dispersal strategies and have insufficient clonal dispersal mechanisms. Conclusions Our results support relatively high grassland regeneration potential from the seed bank in marginal abandoned fields at the landscape level, while suggesting that slow colonizing grassland species with transient seed banks should represent the main targets for reintroduction.