Journal
TREE PHYSIOLOGY
Volume 41, Issue 2, Pages 269-279Publisher
OXFORD UNIV PRESS
DOI: 10.1093/treephys/tpaa121
Keywords
Acer rubrum; Quercus alba; stable isotopes; stomatal pore index; thermal tolerance of photosynthesis; urban forest patch; urban tree physiology
Categories
Funding
- USDA Forest Service Northern Research Station
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The study compared the physiological characteristics of urban forest patch trees with trees growing at reference forest sites, finding that native tree species in urban environment exhibit different responses to urban environments along a latitudinal gradient.
The provisioning of critical ecosystem services to cities of the eastern USA depends on the health and physiological function of trees in urban areas. 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. 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). 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.). The exceptions were delta C-13 and delta N-15, which did not vary in white oak foliage but were significantly depleted (delta C-13) and enriched (delta N-15) in urban red maple foliage. 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. 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. 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. These results demonstrate that differences in native tree physiology occur between urban and reference forest patches, but they are site- and species-specific. Data on local site characteristics and tree species performance over time remain necessary to gain insight about urban woodland ecosystem function.
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