214 Griffin et al: Stem Radius Fluctuations in Urban Trees Arboriculture & Urban Forestry 2021. 47(5):214–231 https://doi.org/10.48044/jauf.2021.019 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & Is the Radial Growth of Irrigated Urban Trees More Strongly Correlated to Light and Temperature than Water? By Kevin L. Griffin, PhD, Thomas G. Harris, Sarah Bruner, MA, Patrick McKenzie, MA, and Jeremy Hise, BA Abstract. Background: Realtime monitoring of tree growth can provide novel information about trees in urban/suburban areas and the myriad ecosystem services they provide. By monitoring irrigated specimen trees, we tested the hypothesis that in trees with sufficient water, growth is governed by environmental factors regulating energy gain rather than by factors related to water use. Methods: Internetenabled, highresolution dendrometers were installed on 3 trees in Southampton, NY, USA. The instruments, along with a weather station, streamed data to a project web page that was updated once an hour. Growing periods were determined using a Hidden Markov Model based on a zerogrowth model. Lin- ear models and conditional inference trees correlated environmental variables to growth magnitude and rate of growth. Results: Growth was governed by the interacting environmental variables of air temperature, soil moisture, and vapor pressure deficit (VPD), and took place primar- ily at night. Radial growth of spruce began April 14 after the accumulation of 69.7 °C growing degree days and ended September 7. Cedar growth began later (April 26) after the accumulation of 160.6 °C and ended later (November 3). During the observation period, these 3 modest suburban trees sequestered 115.1 kg of CO2 . Conclusions: Though irrigated, residential tree growth in our experiment was affected by environ- mental factors relating to both water use and energy gain through photosynthesis. Linking tree growth to fluctuations in environmental condi- tions facilitates the development of a predictive understanding useful for ecosystem management and growth forecasting across future altering climates. Keywords. Carbon Sequestration; Climate; Cryptomeria japonica; Picea glauca; Tree Growth. INTRODUCTION The biogeophysical environment of urban areas is substantially different from that of rural ones. Humans are altering the hydrologic cycle of exurban water- sheds, both by importing vast amounts of fresh water (Booth and Bledsoe 2009), and also through the widespread use of impervious materials that modify the local water balance by decreasing groundwater recharge and increasing surface water runoff (Haase 2009; Walsh et al. 2012). Urban centers modify the local climate by releasing sensible heat from artificial surfaces warmed during the day (McGeehin and Mirabelli 2001; Weng 2003; Hamin and Gurran 2009). Airborne particulates in urban areas can create rain inducing condensation nuclei that result in increased precipitation in, and downwind of, cities (Shepherd ©2021 International Society of Arboriculture et al. 2002). Urban air itself contains increased con- centrations of pollutants such as CO2 , nitrogen oxides, sulfur oxides, ozone, and other volatile organic com- pounds (Chameides et al. 1992; Idso et al. 1998; Lovett et al. 2000; Nowak et al. 2006; Calfapietra et al. 2013). Urban soils often contain elevated levels of heavy metals (Bernhardt et al. 2008; Kaushal and Belt 2012; Sonti et al. 2019). Furthermore, changes in rates of litter decomposition (Carreiro et al. 1999), mineralization and nitrification (Zhu and Carreiro 2004), and shifts in soil faunal communities (Stein- berg et al. 1997) affect local biogeochemical cycles of essential nutrients. Finally, increased abundance of exotic species in urban areas is contributing to signif- icant changes in species composition in urban ecosys- tems (Rudnicky and McDonnell 1989). Understanding
September 2021
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