Climate is a key driver regulating vegetation structure across rural ecosystems. In urban ecosystems, multiple interactions between humans and the environment can act as homogenizing drivers, confounding the relationship between vegetation structure and climate. In fact, vegetation and tree cover of residential neighborhoods frequently appears to be homogenized, and as such, to converge among different urban areas. However, little information exists on the concurrent effects mediated by climate, urban morphology, and socio-economic drivers and how these affect the structural characteristics of vegetation at large spatial scales.
In this study, residential vegetation structure was examined for relationships with urban morphological and socio-economic chacteristics along a large temperature (MAT) and evapotranspiration (PET) gradient in the continental US. Airborne LiDAR and multispectral imagery, collected over nine cities in 2013-15, were used to calculate vegetation structure metrics (i.e., cover, height, volume) in more than 1.4 million residential parcels and 1500 census tracts.
Vegetation volume on residential parcels generally increased with MAT and PET, albeit to a lesser extent compared to that of vegetation in peri-urban areas. Residential vegetation volume was highest in census tracts developed in the 1980s, and more than double the volume of census tracts developed in the 1930s and 2000s. Vegetation volume was higher in census tracts with higher percent home ownership and percent high school graduates. However, as opposed to previous urban tree cover studies, no clear relationships between level of income or racial composition, and vegetation structure were identified.
This study suggests that vegetation across residential parcels in cities located along a large climatic gradient might not be structurally homogeneous. Climate could act as an important biophysical driver at large spatial scales, whereas other socio-economic drivers operate at finer scales. These findings will inform further research needed to evaluate the cascading effects on multiple ecological and hydrological processes related to urban vegetation structure.