The natural regeneration of calcareous grassland at a landscape scale: 150 years of plant community re-assembly on Salisbury Plain, UK

Questions: What is the time-scale for natural regeneration of calcareous grassland? Is this time-scale the same for individual plant species, plant community composition and functional traits? Location: Defence Training Estate Salisbury Plain, Wiltshire, UK. Methods: We investigated the rate of natural regeneration of species-rich calcareous grassland across a 20 000-ha landscape. We combined a large-scale botanical survey with historic land-use data (6-150 yrs before present) and examined differences between grassland age classes in the occurrence of individual plant species, plant community composition and plant community functional traits. Results: Many species showed a significant association with grasslands over 100 yrs old. These included the majority of those defined elsewhere as calcareous grassland indicators, although some appeared on grasslands <10 yrs old. Plant community composition showed increasing similarity to the oldest grasslands with increased grassland age, with the exception of very recently ex-agricultural grasslands. Most functional traits showed clear trends with grassland age, with dispersal ability differing most strongly between recent and older grasslands, whilst soil fertility and pH tolerance were more influential over longer time-scales. Conclusions: Even in a well connected landscape, natural regeneration to a community resembling ancient calcareous grassland in terms of functional traits and plant community composition takes over a century, although changes at the level of individual species may occur much earlier. These findings confirm the uniqueness of ancient calcareous grassland. They also suggest that the targets of re-establishment efforts should be adjusted to account for the likely time-scale of full community re-assembly.