Drivers of Tree Canopy Loss in a Mid-Sized Growing City: Case Study in Portland, OR (USA)

Abstract

The benefits of the urban tree and tree canopy (UTC) are increasingly crucial in addressing urban sustainability. Yet, increasingly evident from earlier research is the distributional inequities of UTC and active efforts to expand tree plantings. Less is known about the dynamics of UTC loss over time and location. This study aims to understand the dynamics of UTC change, especially canopy loss, and to investigate the drivers of the loss. This study draws on a high–resolution dataset of an urban canopy in Portland, Oregon, USA, assessing changes in UTC from 2014 to 2020. By integrating demographic, biophysical, and policy data with UTC information, we use a spatial autoregressive model to identify the drivers of UTC loss. The results reveal an unexpected spatial distribution of UTC change: less gain in the neighborhoods with the least UTC, and greater loss in the neighborhoods with moderate UTC. This study identifies four primary drivers of UTC loss: socioeconomic characteristics, urban form, activities on trees, and residential status. Factors such as population density, race, and income have an impact on canopy loss, as well as the building footprint and the number of multifamily housing units; residential statuses, such as the proportion of owner-occupied housing and residential stability, impact canopy loss.

Evaluating Urban Green Space Inequity to Promote Distributional Justice in Portland, Oregon

“…In urban areas across the states of Oregon and Washington, USA, tree canopy cover increased with median household income [33]. From 2014 to 2020, lower income communities, as well as communities with greater non-white population densities, experienced significant decreases in tree canopy cover compared to whiter and wealthier communities in Portland, Oregon, USA [34]. In Wisconsin, USA, individuals in the lowest income bracket-those making less than $20,000 per year-had the highest likelihood of living in neighborhoods with less than 10% tree canopy cover [35].…”