Tree Moisure Stress and Insect Damage in Urban Areas in Relation to Heat Island Effects

Abstract

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 rdgra 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 (Tingidae 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.

Phenotypic and genotypic divergence of plant–herbivore interactions along an urbanization gradient

“…Urban warming and drought can independently and interactively increase development rate, abundance, and fecundity of herbivorous insects (Dale & Frank, 2014a, 2014b, 2017; Meineke et al, 2013), which may explain why urban aphid populations were larger in the field (Barton & Ives, 2014). Although water stress in plants can enhance aphid performance due to increased nutrient concentrations in the phloem (Cregg & Dix, 2001), A . thaliana had constant shoot and root moisture along our urbanization gradient (lack of urbanization effect on PC2 scores, Table ).…”

Water Availability Determines Tree Growth and Physiological Response to Biotic and Abiotic Stress in a Temperate North American Urban Forest

“…Urban forests mitigate many of the anthropogenic disturbances associated with cities, such as warmer temperatures, carbon emissions, and pollution [1,4]. However, these services can be compromised due to improper plant selection, landscape design, or plant management tactics that reduce resilience to urban conditions [11,17,40]. Impervious surface cover is a ubiquitous feature and cause of high temperatures and dry soil conditions.…”

“…Because of their small size and sedentary life history, sap-feeding herbivores, such as scale insects, often escape detection. Therefore, scale-infested trees, a frequent condition of urban trees, may provide fewer ecosystem services than predicted by models that do not account for these chronic pests [40].…”

Thermal optimum of photosynthesis is controlled by stomatal conductance and does not acclimate across an urban thermal gradient in six subtropical tree species

“…With recent advances in technology such as drones equipped with thermal cameras, it may be possible to measure in situ canopy leaf temperatures more accurately. Going forward, it will be crucial to experiments' to test the potential effect of future climate change on trees and other species (Bussotti et al, 2014;Carreiro & Tripler, 2005;Cregg & Dix, 2001;Farrell et al, 2015). Urban heat islands provide steep thermal gradients with levels of warming on par with predicted climate change for this century and often have planted (i.e., not naturally dispersed) trees that facilitate the separation between adaptive and acclimatory effects-something that is not typically possible in observational studies along large-scale elevation or latitudinal gradients.…”