Vegetative spread is key to applied nucleation success in non-native-dominated grasslands

摘要

Applied nucleation (i.e. planting vegetation patches) is a restoration strategy that better recreates natural ecosystem heterogeneity and requires fewer resources compared to planting the entire area. Whereas applied nucleation shows promise as a forest restoration strategy, this approach has received little study in grassland restoration, where the spread of planted vegetation nuclei may be impeded by aggressive non-native species. We compared the establishment and cover of restored native grass, forb, and rush species for 7 years in applied nucleation and full planting treatments in a former agricultural site dominated by non-natives along the central California coast. We planted seedlings of the same nine coastal prairie species in all treatments, but the applied nucleation plots had four nuclei with only 30% of the seedlings as the full planting plots. We also evaluated the effect of adding wood mulch to reduce non-native plant competition. Native forb cover increased over time and was similar across treatments in the final study year. Native grasses increased for the first 4 years and then declined sharply in all treatments. Native forb cover spread into unplanted areas in applied nucleation plots, whereas grasses showed minimal spread. Of the five planted forb species, the two that persisted until the final study year both spread via rhizomes. Wood mulch reduced non-native cover in the first 2 years and had a longer-term effect on species composition. Our results suggest that applied nucleation can be an effective restoration strategy at a small scale in non-native-dominated grasslands for species that spread vegetatively.