No abstract

The impacts of urbanization, such as urban heat island (UHI) and nutrient loads, can influence tree function through altered physiology and metabolism and stress response, which has implications for urban forest health in cities across the world. Our goal was to compare growth-stimulating and stress-mitigating acclimation patterns of red maple (Acer rubrum) trees in deciduous forests embedded in a small (Newark, DE, US) and a large (Philadelphia, PA, US) city. The study was conducted in a long-term urban forest network on seventy-nine mature red maple trees spanning ten forests across Newark and Philadelphia. We hypothesized that red maples in Philadelphia forests compared to Newark forests will be healthier and more acclimated to warmer temperatures, elevated CO 2 concentrations and reactive nitrogen (N r) deposition, and higher nutrient/heavy metal loads. Therefore, these red maples will have higher foliar pigments, nutrients, and stress-indicating elements, enriched δ 15 N isotopes and increased free polyamines and amino acids to support a growth-stimulating and stress-induced response to urbanization. Our results indicate red maples are potentially growth-stimulated and stress-acclimated in Philadelphia forests experiencing a greater magnitude of urban intensity. Red maples in Philadelphia forests contained higher concentrations of foliar chlorophyll, %N, δ 15 N, and nutrients than those in Newark forests. Similarly, lower foliar magnesium and manganese, and higher foliar zinc, cadmium, lead, and aluminum reflected the difference in soil biogeochemistry in Philadelphia forests. Accumulation patterns of foliar free amino acids, polyamines, phosphorous, and potassium ions in red maples in Philadelphia forests shows a reallocation in cellular metabolism and nutrient uptake pathways responsible for physiological acclimation. Our results suggest the approach used here can serve as a model for investigating 'plant physiology' and the use of urban trees as a biomonitor of the impacts of 'urban pollution' on urban forests. The results suggest that cellular oxidative stress in trees caused by pollutant uptake is mitigated by the accumulation of free amino acids, polyamines, and nutrients in a larger city. Our study provides a framework for determining whether trees respond to complex urban environments through stress memory and/or acclimation.

Transdisciplinary approaches to research involve deliberate integration of theory, methods, and knowledge across disciplines. In disaster studies, transdisciplinarity can be valuable for research teams that span multiple disciplines, offering a framework for identifying problems and proposing solutions in a way that is inclusive of traditional and non-traditional actors. This paper distinguishes transdisciplinary approaches from multidisciplinary and interdisciplinary approaches to disaster research; presents a case study of transdisciplinary disaster research in the U.S. Virgin Islands (USVI) after Hurricanes Irma and Maria; and summarizes key insights about the challenges and opportunities of applying transdisciplinarity in the field. Finally, the authors articulate the importance of transdisciplinary approaches to disaster research and argue for further development for transdisciplinary approaches in disaster research and practice.

Environmental conditions, such as temperature, carbon dioxide, and nutrient availability, are altered by urban conditions at regional scales with potential for impact on tree leaf structure. Our goal was to compare leaf morphological characteristics driven by physiological acclimation in red maple (Acer rubrum L.) trees in deciduous forests embedded in a small (Newark, DE) and a large (Philadelphia, PA) city. The study was conducted in six urban forests on eighteen mature red maple trees in a long-term urban forest network. We hypothesized that red maples in Philadelphia forests compared to Newark forests will have a thicker upper epidermal layer, spongy palisade and mesophyll layer, longer and wider stomates, and lower stomate density. Additionally, we hypothesized that red maples in Philadelphia forests compared to Newark forests will have lower leaf water content and specific leaf area, and greater leaf thickness, fresh leaf weight, dry leaf weight, and leaf dry matter content. Our results for stomate length and stomate width supported our predictions; red maple leaves had longer and wider stomates in Philadelphia forests than in Newark forests. The increased stomate size in red maple trees suggests potential altered gas exchange behavior and mutual abiotic stress mitigation responses in red maple to greater urbanization impacts in Philadelphia forests. This supports previous findings of possible physiological and biochemical acclimation of red maple trees to urban conditions. Furthermore, the findings from this study suggest red maple trees may be a good biomonitor of regional scale impacts in urban environments.Forests and trees have the potential to improve environment quality in urban areas through blockage, uptake, and immobilization of pollutants [12,13]. Plant leaves have the ability to trap, sequester, and compartmentalize pollutants [14,15]. Urban forest trees may also provide important benefits through pollution regulation of urban conditions. However, this is debatable due to biogenic volatile organic compound (BVOC) production by urban trees [16 ], and for some pollutants, like particulates, the aerodynamic effect of tree canopies can influence particulate residence time, recirculation, and concentration in urban environments [17,18]. Alternatively, urban air pollutants can affect tree growth and function; tropospheric ozone has been reported to induce visible injuries, de-regulate stomatal conductance, and reduce photosynthesis and leaf area [19,20]. These complex interactions with urban tree canopies and atmospheric pollutants may stress trees, leading to shorter lifespan even with enhanced growth rates [21]. Thus, the ability of urban trees to mitigate urban conditions and improve environment quality and sustainability of cities may be dampened by their response to altered urban environmental conditions [17,22,23].The morphological and anatomical traits in leaves can serve as a bioindicator of plant response to altered environmental conditions, specifically air [15,24] and soil [2,25,26] polluti...