COS 271-5 - Sourcing seed for restoration in an urban landscape

Abstract: Restoration is challenging in urban areas due to heterogeneity in abiotic conditions such as nitrogen deposition rates and heat severity, and biotic conditions such as percent natural cover. Additionally, we know little about how variability in urban environments may impact species’ demographic or functional traits. We used the native perennial shrub Eriogonum fasciculatum (California buckwheat), which is common throughout urban areas in Southern California and a popular candidate for restoration projects, to assess how different urban environments have shaped variability in intraspecific traits. We collected seeds from 14 populations within the urban footprint of the Los Angeles metropolitan area, CA, USA. We tracked germination, growth, and first year survival of individuals grown from each source location in a common garden also located in the Los Angeles metropolitan area. Alongside demographic data, we measured functional traits to see if plants sourced from different urban environments exhibited altered resource-acquisition strategies. Compared to individuals sourced from areas with greater than 70% natural cover, individuals sourced from areas with less than 70% natural cover had an average of 10% higher germination probability and seedlings were 7% more likely to survive their first year. Individuals sourced from areas with less natural cover areas also had 3.5 μg more leaf nitrogen and were, on average, 0.34 cm taller within the first two months of growth than individuals sourced from areas with more natural cover. Individuals sourced from areas with a high Urban Heat Index (UHI) were more water use efficient than those sourced from areas with a low UHI; however, the UHI in Los Angeles is confounded with a natural heat gradient. We found no effect of nitrogen deposition on any of the measured variables. Overall, we found strong evidence for variation in demographic rates and some evidence for variation in functional traits in a perennial shrub across populations in a highly urbanized but abiotically diverse metropolitan area. We conclude that differences in urban-sourced E. fasciculatum could be leveraged to overcome barriers to restoration in urban areas during establishment, but more research is needed on population genetics and long-term demographic and additional functional traits to ensure that urban-sourced species are not more susceptible to other anthropogenic stressors, including increased variability in temperature and precipitation brought on by climate change, or increased invasion by non-native species.