![]() Previous studies have shown evidence of tree physiological responses to the environment of individual cities, but it is not clear whether the same species responds similarly across different urban areas. However, variation in urban forest patch soil quality may lead to differences in native tree growth and physiology within an urban area, making it important to capture forest patch heterogeneity within a city ( Pregitzer et al. 2012), and the soils of urban forest patches may actually have greater nutrient availability than reference forest sites ( Pouyat et al. However, warmer nighttime air temperatures at urban sites may allow for higher rates of photosynthesis without causing additional drought stress ( George et al. ![]() 2015), despite some research to the contrary ( Zhao et al. There is an assumption that the urban environment (i.e., increased air temperatures and pollution) is inherently stressful to plants ( Calfapietra et al. ![]() ![]() Furthermore, native wildtype trees found in forest patches may exhibit different physiological function than planted tree cultivars found in highly managed settings ( Lahr et al. Although we know that the urban environment can reduce the productivity of trees planted in highly developed areas ( O'Rourke and Terjung 1981, Sjöman and Nielsen 2010, Dale and Frank 2014, 2017), it is not clear that trees in urban forest patches experience the same stressful environmental impacts. However, the provisioning of these ecosystem services depends on the health and physiological function of trees in urban forest patches, which may be impacted by the surrounding urban land use ( Cadenasso et al. 2019), and may have a higher capacity to provide critical biophysical ecosystem services than more intensively managed park areas ( Vieira et al. Urban woodlands, or forest patches, make up a significant proportion of many cities’ tree canopy cover (e.g., Avins 2013, Pregitzer et al. In the eastern USA, trees are dominant components of urban ecosystems, providing valuable biophysical and sociocultural ecosystem services to urban residents. The ability of plants to persist in urban landscapes will determine their capacity to mitigate aspects of the urban environment that are stressful for human inhabitants, including increased air temperature, flooding and pollution ( Volder 2010, Calfapietra et al. Data on local site characteristics and tree species performance over time remain necessary to gain insight about urban woodland ecosystem function. These results demonstrate that differences in native tree physiology occur between urban and reference forest patches, but they are site- and species-specific. Stomatal pore index (SPI) showed inter-specific differences, with red maple SPI being higher in urban trees, whereas white oak SPI was lower in urban trees. However, the highest average values of T crit were found in the Baltimore urban white oaks, suggesting that species suitability and response to the urban environment varies across a latitudinal gradient. Across all sites, red maples had higher thermal tolerance of photosynthesis ( T crit) than white oaks, suggesting a greater ability to withstand temperature stress from the urban heat island effect and climate change. The exceptions were δ 13C and δ 15N, which did not vary in white oak foliage but were significantly depleted (δ 13C) and enriched (δ 15N) in urban red maple foliage. Overall, white oaks ( Quercus alba L.) show more differences in chlorophyll fluorescence parameters and leaf traits by city and site type (urban vs reference) than red maples ( Acer rubrum L.). In this study, we examine chlorophyll fluorescence parameters, leaf traits, foliar nutrients and stable isotope signatures of urban forest patch trees compared with trees growing at reference forest sites, in order to characterize physiological response of these native tree species to the urban environment of three major cities arranged along a latitudinal gradient (New York, NY Philadelphia, PA Baltimore, MD). Although we know that the urban environment may be stressful for trees planted in highly developed areas, it is not clear that trees in urban forest patches experience the same stressful environmental impacts. The provisioning of critical ecosystem services to cities of the eastern USA depends on the health and physiological function of trees in urban areas.
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