Linking Urban Forest Hydrology, Ecosystem Services, and Remote Sensing of Biodiversity

Abstract:

In arid cities the benefits of an urban forest are dependent on regular irrigation, which creates a trade-off between excessive water use and vegetation-derived ecosystem service such as microclimate cooling. These urban forests are also functionally biodiverse, exhibiting a broad range of ecological strategies of water usage and stress response. In a warming climate, certain urban forest species could be at risk of mortality due to loss of function, or use excessive amounts of water to mitigate high temperatures and aridity. Identifying the heat stress response of urban tree species will be a key factor in planning the next decades of urban forest.

As urban forests are planted across multiple jurisdictions, remote sensing of function can prove very useful in detecting heightened stress responses. Using an experimental plantation of 12 species of irrigated urban trees in Southern California, we resolve linkages between leaf-level physiological stress responses, remote sensing of biodiversity, and ecosystem services of vegetation-derived cooling. We use high-resolution UAV multispectral imagery to link vegetation (NDVI) and thermal imagery (LST), with species specific physiological properties of photosynthesis, transpiration, and leaf water potentials ( Ψleaf ). As well as the resulting ecosystem services of localized air cooling. By comparing canopy LST and under canopy air temperature with reference temperature during extreme heat events, we identify the species tradeoffs between water usage and microclimate cooling.

Preliminary results have identified an NDVI range of 0.149 and a mean canopy temperature range 4.22°C across tree species. The delta Ψleaf (Pre-dawn - Mid-day) has a range from -0.05 kPa to 2.26 kPa across species. These wide species-specific ranges highlight the functional variability within the urban forest, and the multiple hydraulic strategies. Through linking in-situ measurements of photosynthesis, transpiration, and leaf water potential, with high-resolution UAV sensed NDVI and canopy LST, we will identify remotely sensed indicators of tree stress, and highlight the species specific variation in urban forest traits and services.