Tree moisture stress and insect damage in urban areas in relation to heat island effects

The objectives of the study were to 1) quantify the extent of the urban heat island effect between trees growing downtown and those growing on less-developed sites on campus; 2) compare plant water relations and gas exchange of three tree species on both sites; 3) compare insect pest abundance and insect damage between trees growing downtown and on campus. [UMN]

"We monitored crown air temperature, volumetric soil moisture, leaf water potential, rates of gas exchange, and insect pests of green ash (Fraxinus pennsylvanica ‘Marshall’s Seedless’), Austrian pine (Pinus nigra Arnold), and northern red oak (Quercus rubra L.) trees during a relatively hot summer in Lincoln, Nebraska, U.S. Air temperatures and vapor pressure deficits (VPD) were much higher in trees growing downtown than in nearby trees growing on the University of Nebraska campus. Increased VPDs and reduced soil moisture decreased pre-dawn water potential and gas exchange of ash and oak trees on the downtown site compared to trees on campus. Green ash trees downtown had more damage from lilac borers (Podosesia syringae (Harris) (Sesiidae)) than did trees on campus. Aphids (Aphidiae) and lace bugs (Corythucha arcuata (Say)) appeared to be more numerous on oak trees growing downtown than on those growing on campus. Cultural treatments that improve soil moisture availability, such as irrigating, increasing planter size, and mulching, are especially critical on heat island sites and may reduce tree stress, pest damage, and mortality." [Abstract]