Historical Urban Tree Canopy Cover Change in Two Post-Industrial Cities

Present-day spatial patterns of urban tree canopy (UTC) are created by complex interactions between various human and biophysical drivers; thus, urban forests represent legacies of past processes. Understanding these legacies can inform municipal tree planting and canopy cover goals while also addressing urban sustainability and inequity. We examined historical UTC cover patterns and the processes that formed them in the cities of Chelsea and Holyoke, Massachusetts using a mixed methods approach. Combining assessments of delineated UTC from aerial photos with historical archival data, we show how biophysical factors and cycles of governance and urban development and decay have influenced the spatiotemporal dynamics of UTC. The spatially explicit UTC layers generated from this research track historical geographic tree distribution and dynamic change over a 62-year period (1952-2014). An inverse relationship was found between UTC and economic prosperity: while canopy gains occurred in depressed economic periods, canopy losses occurred in strong economic periods. A sustainable increase of UTC is needed to offset ongoing losses and overcome historical legacies that have suppressed UTC across decades. These findings will inform future research on residential canopy formation and stability, but most importantly, they reveal how historical drivers can be used to inform multi-decadal UTC assessments and the creation of targeted, feasible UTC goals at neighborhood and city scales. Such analyses can help urban natural resource managers to better understand how to protect and expand their cities' UTC over time for the benefit of all who live in and among the shade of urban forests.

Automated summary

Present-day spatial patterns of urban tree canopy are shaped by the interaction between human and biophysical factors, reflecting legacies of past processes. Understanding these legacies can guide urban tree planting goals, promote urban sustainability, and address equity issues. Through a mixed methods approach, we investigated historical tree canopy cover patterns and their formation processes in Chelsea and Holyoke, Massachusetts. Our findings reveal an inverse relationship between tree canopy and economic prosperity, with gains occurring in periods of economic decline and losses in periods of economic growth. To overcome historical legacies and ongoing losses, sustainable increases in urban tree canopy are required. These insights can inform future research on residential tree canopy formation and stability, as well as the establishment of targeted and feasible canopy goals at the neighborhood and city scales. Such analyses contribute to the understanding of how to protect and expand urban tree canopy over time for the benefit of all residents.