Plant community dynamics of native plant assemblages on geographically isolated green roofs
Biodiversity and ecosystems services of green roofs are hypothesized to increase with the use of native and non-succulent vegetation on green roofs, yet studies indicate that plant survivorship of these plant species varies greatly. Therefore, plant colonization dynamics may play an important role in green roofs that are planted with non-succulent native plant species. Plant colonization may depend on planted assemblage species composition, gaps in vegetation cover, the available colonist species pools, and seasonality. Two years after two different native assemblages were planted on ten geographically isolated green roofs, survivorship and cover of the planted species were estimated and all plants that colonized into the plots following establishment were harvested, identified to species, dried and weighed in June, July, and August 2012.
Species identity explained 35.6% of the total variation in survivorship and there was a significant effect of assemblage on plant colonist composition, suggesting possible priority effects on colonization dynamics. Greater resident assemblage cover generally decreased plant colonist biomass and richness. Plant colonist composition differed among geographically isolated green roofs and between the June and August sampling periods. The results from this study indicate that patterns of plant composition in green roofs planted with non-succulent native plant species assemblages depends on effects at temporal, regional, and local scales. These results may help develop strategies to manage perennial plant assemblages on green roofs, which may help maintain urban biodiversity and mitigate environmental degradation.