Grassland species colonization of a restored grassland on a former forest varies in short-term success but is facilitated by greater functional connectivity

In recent years, restoration on former grassland sites has been widely encouraged globally, aiming to address the historical loss of 90% of ancient species-rich grasslands, and to mitigate the associated threat to grassland biodiversity. The objective of our study was to investigate on a small-scale how plant species spontaneously colonize restored grasslands. We inventoried 275 permanent plots twice (in 2019 and 2021) in a restored grassland, following the removal of a conifer plantation. Species richness and vegetation cover in surveyed plots were dependent on grazing activity and distance to adjacent grassland. Plant species associated with forest habitats declined, while the occurrence of generalist species together with a few grassland specialists generally increased. However, not all grassland specialists gained occurrence and the colonization pattern was not consistent over time, possibly due to the lack of continuous seed arrival and low livestock activity and hence lack of disturbance. These results suggest that successful colonization of plant species benefits from links to species-rich sites adjacent to the restoration target, with spatial dispersal and improved conditions for species establishment being key to species occurrence. Both dispersal and establishment potential are likely facilitated through the presence of grazing livestock with access to both species-rich grasslands and restoration targets. However, the shift towards a more typical grassland community takes place gradually, with vulnerable populations of early colonizing grassland species prone to local extinction in short-term. As a result, continued functional connectivity provided by grazing animals is necessary to improve the diversity of the restored site and ensure the establishment of grassland specialists and to maintain the plant community composition.

Automated summary

In recent years, global efforts have been made to restore former grassland sites in order to address the loss of ancient species-rich grasslands and protect grassland biodiversity. This study examined how plant species spontaneously colonize restored grasslands in a small-scale setting. The results showed that grazing activity and distance to adjacent grassland influenced species richness and vegetation cover. Forest-associated plant species declined, while generalist species and some grassland specialists increased. However, not all grassland specialists successfully colonized the restored grasslands and the colonization pattern varied over time. The presence of grazing livestock, continuous seed arrival, and disturbance are crucial for successful colonization and establishment of plant species.