Linking Urban Tree Cover Change and Local History in a Post-Industrial City

Lara Roman,Eric Greenfield,Jason Henning,Indigo Catton,Hamil Pearsall,Theodore Eisenman

doi:10.3390/land10040403

Abstract

Municipal leaders are pursuing ambitious goals to increase urban tree canopy (UTC), but there is little understanding of the pace and socioecological drivers of UTC change. We analyzed land cover change in Philadelphia, Pennsylvania (United States) from 1970–2010 to examine the impacts of post-industrial processes on UTC. We interpreted land cover classes using aerial imagery and assessed historical context using archival newspapers, agency reports, and local historical scholarship. There was a citywide UTC increase of +4.3 percentage points. Substantial UTC gains occurred in protected open spaces related to both purposeful planting and unintentional forest emergence due to lack of maintenance, with the latter phenomenon well-documented in other cities located in forested biomes. Compared to developed lands, UTC was more persistent in protected open spaces. Some neighborhoods experienced substantial UTC gains, including quasi-suburban areas and depopulated low-income communities; the latter also experienced decreasing building cover. We identified key processes that drove UTC increases, and which imposed legacies on current UTC patterns: urban renewal, urban greening initiatives, quasi-suburban developments, and (dis)investments in parks. Our study demonstrates the socioecological dynamism of intra-city land cover changes at multi-decadal time scales and the crucial role of local historical context in the interpretation of UTC change.

Highlights

In light of the aforementioned research needs and gaps, we investigated the spatiotemporal dynamics of urban tree canopy (UTC) in Philadelphia, Pennsylvania (US) from 1970–2010, a postindustrial period marked by substantial human population loss
Our findings concur with previous research indicating that UTC gains result from the conversion of agricultural lands to low-density residential developments [24], forest emergence on abandoned and/or unmaintained lands [8,10], and concerted efforts to plant trees and create new parks [23,29]
Our findings reveal that the influence of redevelopment on the urban forest was not limited to urban renewal projects of the 1950s–1970s, as Philadelphia’s mayoral initiative to tear down abandoned buildings in the early 2000s sponsored a vacant lot greening program

Summary

Introduction

Long-term land cover change assessments are needed to understand the pace and process of urban tree canopy (UTC) gains and losses. UTC refers to the proportion of land covered by trees when viewed from above [1]. The spatial patterns of UTC within cities often correlate with income and race [2,3], population and building density [4,5], and topography [6], with important idiosyncrasies in these generalities related to local sociopolitical history [7]. Legacies of shifting urban form (e.g., change to suburban-style housing) and sociodemographic change (e.g., increasing concentrations of wealth, human population spikes or crashes) shape UTC spatial patterns [8]. The spatiotemporal patterns of UTC within a given city are reflective of complex interactions over time between biophysical and human drivers [8]

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