Roman_et_al_2021
Roman L, Catton I, Greenfield E, et al (2021) Linking Urban Tree Cover Change and Local History in a Post-Industrial City. Land 10:403. https://doi.org/10.3390/land10040403
Keywords: aerial imagery, land cover, legacy effects, canopy cover, urban forest, environmental justice, race
Urban tree canopy (UTC) is often correlated with income, race, population and building density, and topography. Legacies of urban form and sociodemographic change also shape UTC patterns. Time lag of tree maturity means that multi-decadal time scales are required to see shifts in UTC. Shifts from urban/agricultural -> suburban have seen increases to UTC but relationship is not always present. It is critical to incorporate historical information. Urbanization/shrinkage/land-use change is not uniform and often has very complex relationships with the history of a place. Looked at specific mechanisms of UTC change. Visually interpreted aerial imagery to assess land cover change. UTC increased most in protected open areas (parks) and most change occurred from switching herbaceous land cover to treed land cover. Open protected areas were also more stable in tree presence. Different planning districts have different changes in UTC but none experienced a loss of UTC. Generally, UTC increases were derived from losses in herbaceous cover, with one planning district experiencing a decrease in building cover. The urban renewal period saw the city expanding into surrounding agricultural land. Urban decline led to disinvestment from municipal parks, leading to urban greening efforts by local NGOs. Also, several large tracts became private/state/federal parks. Former agricultural and rural lands transformed into suburban/industrial landscapes reduced herbaceous cover, increased building/impervious/UTC cover. Municipal parks experienced largest gain of UTC of any classification - also had the most stable UTC with 90% of trees present 40 years ago persisting to today. Divestment in park budgets results in unmaintained parks with unintentional forest emergence - causing increase in UTC. Specific planting initiatives also increased UTC in parks. Land cover transitions were linked across the city. UTC gains occurred across socioeconomic lines but the historical angle is extremely important - high-density neighbourhoods had less space for planting but experienced more UTC gains than neighbourhoods with more space but higher % of black people. Philadelphia did not experience major invasive pests during study time frame.