What makes an effective tree preservation ordinance? Analyzing relations among tree preservation actions and canopy cover

Source abstract

The values that large healthy trees provide to cities are well established. Many cities use tree preservation ordinances to protect trees on private property. To assess the effectiveness of tree preservation ordinances, we use a regression framework to analyze the correlation among preservation actions and canopy cover change. Our dataset contains environmental and demographic information on census block groups of 62 cities in 4 U.S. states, as well as coded text from each city’s tree preservation ordinance. We found evidence that inclusion of more preservation actions is weakly correlated with better canopy outcomes. As well, census blocks with city codes that fulfill five or more preservation actions have less canopy cover loss than blocks with codes that have one to four. We also found that canopy growth was correlated with certain demographic variables (e.g., unemployment) and that development and population in poverty were correlated with greater canopy loss. Given the urgency to protect urban tree canopies from development pressures and climate change, we identify additional variables that could account for canopy change and suggest a quasi-experimental design for future studies on preservation code effectiveness.