Urban greenspaces are recognized to have beneficial impacts on the health and wellbeing of urban residents; however greenspaces are often not distributed uniformly within a city. Furthermore, due to the strong influence of human choice and decision-making – both by individuals and collectively in institutions – urban landscapes have significant variability in water and nutrient inputs, infiltration capacity (water availability), microclimate (based on proportion of vegetation to artificial surfaces), and biological composition. These factors likely result in high variability in the quality of urban greenspaces, but the relative importance of these different drivers is unclear. As one of the geographically largest cities in the US, Oklahoma City, Oklahoma has a range of land covers and microclimates, as well as diverse actor groups. Using ground- and aerial-image-based surveys, we investigated spatial variability in urban tree health and mortality and landscape sensitivity to drought. Our objectives were to determine 1) How much spatial variability is there in urban tree and greenspace condition and sensitivity to water stress? 2) What are the primary climatic, landscape, and social correlates with greenspace quality and sensitivity of greenspaces to extreme climate events such as drought?
Results/Conclusions
As expected, we found substantial variability in the average condition of trees across public greenspaces/parks, ranging from an average condition of 1.5 to 3.3 (on a 5 point scale). Tree condition was generally worst for the youngest and oldest trees (and those in the newest and oldest parks). This likely reflects the difficulty of young tree establishment (with mortality rates of ~40%), and the accumulation of human and climate induced damage in long lived trees. Tree species rated as highly drought tolerant had ~20% higher average condition than those rated moderately drought tolerant. At a broad scale, urban lawns were far more response to drought conditions than urban trees. Investigation is under way to better incorporate neighborhood scale social and demographic data, to understand how these may be related to greenspace quality and tree condition. Ultimately, this helps us to understand the distribution of greenspace benefits across urban ecosystems, and how human drivers may influence the sensitivity of landscapes to extreme drought.