Linking tree cover change to historical management practices in urban parks

Abstract

Urban tree canopy (UTC) in parks is shaped by complex interactions between social and ecological processes over decades. To understand UTC change in parks, it is critical to identify and characterize the unique set of social processes that drive long-term change. We sought to uncover the feedbacks between social processes and long-term UTC changes in parks of a post-industrial city that experienced substantial population loss and park disinvestment. Our mixed-methods approach involved quantifying spatiotemporal UTC changes and connecting those changes to historical management practices for three parks in Philadelphia, PA (US). We delineated UTC using aerial imagery between 1959 and 2018, and synthesized information from archival records and semi-structured interviews about historical management practices. We found substantial UTC gains between 1959 and 1980, due to both: (a) budget cuts, mowing cessation, and associated unintended forest emergence; and (b) purposeful tree planting and reforestation activities. While some UTC gains were purposeful, others were unintentional and reflect successional processes on unmaintained lands. Contrary to literature suggesting that financial investment would lead to UTC gain, we saw declining UTC following an influx of new funding post-2000 due to construction and ecological restoration. We found differing pathways leading to convergent outcomes of UTC gains. Across the three parks, differing historical processes and management goals for park landscapes had important ramifications for UTC. Our work suggests that landscape management could benefit from an improved understanding of how historical processes impact land cover over the long-term.