Effects of woody species encroachment and fire on vegetation and the soil seed bank in dry grasslands of Transylvania

Abstract

Abstract Questions (a) In which ways do woody species encroachment and fire affect vegetation and seed bank composition, structure and diversity in Transylvanian dry grassland; (b) do native and non‐native woody species differ with respect to their impact on grassland community composition and structure; (c) is burning useful to control woody species encroachment; and (d) can soil seed banks contribute to the restoration of grasslands in Transylvania? Location Transylvania, Romania. Methods We collected data on vegetation and seed bank composition in 4 m 2 plots in 16 shrub‐encroached grasslands and adjacent open grassland. Data were analyzed with regard to the impact of woody species encroachment (native vs non‐native) and fire on grassland vegetation and the seed bank using NMDS and LME models combined with ANOVA and Tukey contrast tests. Results Encroachment was accompanied by a decrease in plant species diversity and altered microclimatic conditions. There was a lack of sufficient evidence for a difference in effect size between native and non‐native woody species on tested vegetation or seed bank parameters. While the effects of fire on vegetation were weak compared to encroachment, burning failed to reduce the cover of woody species sustainably. Grassland vegetation and the seed bank differed significantly in species composition and diversity, indicating a limited potential for restoration from the seed bank alone. Conclusions To halt secondary succession in Transylvanian grassland sustainably, we suggest the establishment of a post‐fire management regime including the cutting of woody species and/or re‐introduction of grazing and mowing. Grassland restoration from the seed bank may be supported by the introduction of species from surrounding intact grassland.