Characterizing urban forest functioning and ecosystem services with digital imaging

2013 | Mitchell Pavao-Zuckerman, University of Arizona

This project focuses on the ability of the urban forest in semi-arid cities to provide ecosystem services related to microenvironments, how individual trees scale up to provide shade locally and affect urban heat islands, and ultimately how the urban forest impacts human well-being. I propose to utilize a suite of photography tools to develop assessment protocols: hemispherical photographs to assess energy inputs through the urban forest canopy, hyperspectral imaging to assess plant functional status, and thermal imaging to gauge shading impacts on surface temperatures. These data will be collected in conjunction with tree size and growth parameters, and together, will allow evaluation of existing models of urban tree and forest energy benefits in comparison with data collected from real trees in a real urban context.

The project will take place in Tucson, AZ, a semi-arid city with a strong history of tree planting for human benefit, a recent emphasis on the use of native and desert-appropriate species, and an urban forest initiative that is supported by local government, industry, and non-profit organizations. I will leverage connections to these programs to disseminate findings from the project, and also make use of my position with Biosphere 2 to reach a broad public audience. This project will lead to the development of new tools to assist arborists in the evaluation of the ecosystem services provided by urban forests.

Research Findings

The ability of urban forests to provide ecosystem services is critical for mitigating environmental impacts of cities and ultimately for making cities livable. New approaches to assess the function of urban forests and their services are critical for demonstrating connections to well-being in cities and going beyond static assessment calculator approaches. Understanding the variability in service provision would be facilitated by approaches that capture a great deal of data in little time. 

To address this need, we adopted approaches to assess urban forests that make use of digital imaging systems (hemispherical, infrared, and hyperspectral photography to characterize incoming radiation, thermal environment, and plant functional status, respectively) and compared them to traditional forestry methods. We focused on traits and services related to shading and local microclimate; important services in the semi-arid southwest (where our study site, Tucson, AZ, is located). We focused on a few common native and non-native tree species in park and street-scape settings. Strong, positive relationships were found between tree size and height and their ability to provide energy saving ecosystem services.

We found shading capacity as determined by the camera systems to be more variable than traditional assessment tools. And this variability was often related to the growth form of the plant. The shading index derived from the camera systems and the shade energy savings determined by traditional forestry methods and ecosystem service calculators were positively correlated. This initial data set suggests that camera systems may be an efficient tool for rapidly collecting large amounts of data on urban forests and their ecosystem services.