How site context and restoration practices influence native plant community assembly outcomes across urban-rural gradients

Background/Question/Methods

There is increasing interest in and need to restore native plant communities, especially within urban areas. However, very few studies have tested the consequences of restoration or management practices in urban contexts for plant communities. Urban areas are distinct from non-urban areas; they support diverse, often novel, species assemblages and altered environmental conditions relative to non-urban systems where much of restoration ecology research has taken place. Whether we can extend current knowledge and tools from restoration ecology to urban systems remains a large gap in our understanding. We lack understanding of fundamental questions, like: what factors structure variation in restoration outcomes in urban settings? To identify these factors, I surveyed 30 urban prairie restoration plantings across three cities in southern Michigan. I collected plant community abundance and composition data in 1x1m plots along a 20 m transect and composition of the whole site through a walk through. Additionally, I collected data about the restoration and management practices, soil compaction, soil water holding capacity, and a measure of shading. To understand how site conditions impacted among site variation in diversity and community composition, I used an unconstrained ordination, a permutational multivariate analysis of variance, and general linear models.

Results/Conclusions

An unconstrained ordination revealed that plant community composition is associated with gradients of soil compaction, soil water holding capacity, and shading, while not associated clearly with the three cities surveyed. Differences in the species richness were tested using a general linear model which found only very weak support that site abiotic conditions such as soil compaction and the amount of shade these restoration plantings experience are driving differences among the restored plant communities surveyed. Increases in soil compaction and shading resulted in decreases in plant species richness. No significant predictors were found for plant community diversity. Further, there wasn’t a clear relationship between community composition or diversity with the age of the restoration planting. This result was surprising; non-urban studies have typically found a negative relationship between species richness and restoration age. Overall, these results indicate that while the site conditions measured are impacting community composition, much of the among-site variation was unexplained by these factors. More work needs to be done to extend our knowledge of restoration ecology to urban areas in order to identify the impact of abiotic conditions and restoration and management practices across restored plant communities in urban areas.