Arboriculture & Urban Forestry

Background: Urban tree canopy (UTC) is often proposed as a mitigation strategy for simultaneously decreasing carbon emissions and urban heating in cities. Not only can trees reduce outdoor temperatures through shading and transpiration, but research also suggests that microclimate regulation by trees surrounding buildings can lead to cooler indoor temperatures and a subsequent decrease in summertime energy use. Methods: We analyzed summertime cooling electricity consumption for 21,048 single-family homes in a semi-arid city in northern Colorado, USA. Using Pearson’s correlation coefficients and multiple linear regression models, we evaluated the potential impact of UTC on cooling electricity use in 16 different zones around each house. We hypothesized that trees closer to the home, and trees located on the west and south sides of homes, would have the greatest impact on cooling electricity use. Results: UTC in all 16 zones around residential buildings was associated with negative correlation coefficients, indicating that UTC may be having an impact on energy use. Our regression results showed that UTC on the east side of single-family homes had the greatest effect. Conclusions: Although our results indicated that trees in landscapes around residential buildings can lead to some decreases in household-level energy consumption, the reductions in electricity usage were not as substantial as previous studies have predicted. Past research has shown that tree location matters, and our results indeed show that where UTC is located in reference to a building can change how much impact trees have on energy use. However, our results also show that trees on the east side of buildings have the most impact on household energy consumption in a semi-arid city in Colorado during the summer months. These results directly contradict predictions offered by popular ecosystem service models that show trees on the west and south sides of buildings as having the most impact on energy use in the Northern Hemisphere. Furthermore, many studies have suggested that the energy benefits provided by urban trees outweigh their carbon sequestration potential, and our results indicated this assumption may not hold true in all cities. 1 CEU (A, U, M, Bs, Bm)

Utility vegetation managers need tools to predict tree-related risks and knowledge of the necessary management prescriptions to reduce the risk of windthrow damage to utilities’ electrical infrastructure. This review focuses on key studies involving the likelihood of failure of trees, beginning with a description and discussion of failure in trees, followed by an examination of methodologies that have been used to assess tree failure, before concluding with a review of factors which have been found to influence tree failure. Ultimately, a better understanding of the likelihood of failure of individual trees and the relationships governing tree failure and vegetation-related outages may allow for significant advances in the risk management of utility infrastructure. 1 CEU (A, U, M, T, L, Bm)

Studies assessing the effects of biochar used as a soil amendment in agriculture and forestry have indicated variable results, from significant improvements in growth and health to no effect at all. Research into biochar use for trees within the urban landscape is extremely limited. This review is aimed at arboricultural practitioners and professionals involved in urban tree landscape management and provides a critical analysis of the use of biochar to support tree health and establishment. Biochar, specifically wood biomass-based biochar, has the potential to enhance tree establishment and survival. However, considerable variability in the physical and chemical properties of biochar currently limits universal application. Therefore, practitioners should aim to use biochar types suitable for the desired function, such as transplant establishment, remediation of declining mature trees, and pest/disease management. Biochar also represents a promising complementary amendment to more established soil management techniques such as mulching and fertilization, but further long-term studies in a range of conditions typical of urban environments are required to fully understand the effects of specific biochar types on urban trees. 1 CEU (A, U, M, T, L, Bs, Bp)

Background: As human populations urbanize, urban forests in many areas are decreasing in canopy extent due to disruptions on several fronts, including novel pests and diseases, climate change, and changing land uses. Methods: A review of the remote sensing, computing, and environmental literature was performed to provide an overview of current technology capabilities and to detail an agenda for a modern approach to urban forestry challenges. How to prepare current and future professionals to collect and analyze “Big Data,” how to implement results, and what communication skills are needed in a modern world to provide resilient urban forests in the connected future were also reviewed. Results: This paper outlines an agenda for how the urban forestry professions can identify, analyze, and manage emergent disruptions to continue to provide urban forest benefits to residents in its shade. Current remote-sensing systems, the paradigm of Big Data, and collection and analysis platforms are discussed, and relevant scenarios are provided to guide insight into managing forests with a rejuvenated perspective using remote-sensing hardware and software. Conclusions: Modern cities will require modern digital urban forestry management, and current and future professionals must be able to access and utilize technology, sensors, and Big Data to effectively perform vegetation management and communication tasks. This paper details the framework for a new era of modern urban forest management in highly connected, resilient cities. 1 CEU (A, U, M, T, L, Bm)

Urban forests create indispensable habitat for declining wildlife populations. The tree care industry is essential to the viability of urban forests and thus the survival of urban wildlife. At the same time, tree care operations such as tree removal and branch pruning present clear threats to urban wildlife and their habitats. Here we describe the development of a grassroots coalition of arborists and wildlife advocates in the Western United States and the process of charting a path to best management practices and professional training to mitigate the impacts of tree care practices to wildlife. In particular, we describe the unique challenges and opportunities that arose through this multidisciplinary process and build a case for the benefits of uniting diverse communities of practice around complex urban ecological problems. We finish by laying out recommendations to the international arboriculture and urban forestry practitioner and research communities. 0.5 CEU (A, U, M, Bm, Bp)

Background: We present the plant area index (PAI) measurements taken for 63 deciduous broadleaved tree species and 1 deciduous conifer tree species suitable for urban areas in Nordic cities. The aim was to evaluate PAI and wood area index (WAI) of solitary-grown broadleaved tree species and cultivars of the same age in order to present a data resource of individual tree characteristics viewed in summer (PAI) and in winter (WAI). Methods: All trees were planted as individuals in 2001 at the Hørsholm Arboretum in Denmark. The field method included a Digital Plant Canopy Imager where each scan and contrast values were set to consistent values. Results: The results illustrate that solitary trees differ widely in their WAI and PAI and reflect the integrated effects of leaf material and the woody component of tree crowns. The indications also show highly significant (P < 0.001) differences between species and genotypes. The WAI had an overall mean of 0.91 (± 0.03), ranging from Tilia platyphyllos ‘Orebro’ with a WAI of 0.32 (± 0.04) to Carpinus betulus ‘Fastigiata’ with a WAI of 1.94 (± 0.09). The lowest mean PAI in the data set was Fraxinus angustifolia ‘Raywood’ with a PAI of 1.93 (± 0.05), whereas Acer campestre ‘Kuglennar’ represents the cultivar with the largest PAI of 8.15 (± 0.14). Conclusions: Understanding how this variation in crown architectural structure changes over the year can be applied to climate responsive design and microclimate modeling where plant and wood area index of solitary-grown trees in urban contexts are of interest. 1 CEU (A, U, M, Bs)

Real-time 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. Internet-enabled, high-resolution 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 zero-growth model. Linear models and conditional inference trees correlated environmental variables to growth magnitude and rate of growth. Growth was governed by the interacting environmental variables of air temperature, soil moisture, and vapor pressure deficit (VPD), and took place primarily 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. Though irrigated, residential tree growth in our experiment was affected by environmental factors relating to both water use and energy gain through photosynthesis. Linking tree growth to fluctuations in environmental conditions facilitates the development of a predictive understanding useful for ecosystem management and growth forecasting across future altering climates. 1 CEU (A, U, M, Bs, Bp)

The shoots produced from axillary, epicormic, and lignotuberous buds are significant parts of stress recovery responses in many tree species. The production of either epicormic or lignotuberous shoots does not guarantee survival of a tree, as the mortality of shoots is high. This research investigated the relationship between root tip growth and shoot production and survival after stress and its implications for urban tree managers. Seedlings of Eucalyptus obliqua L’Herit. were stressed by decapitation or different levels of heat stress at temperatures ranging from 40 °C to 100 °C for 2 to 128 minutes, as well as combinations of the two stresses. While the temperatures are not as high as those experienced in a forest fire, the stresses imposed can inform plant responses to stress such as fire. Lower temperatures and shorter durations were often sublethal, and decapitation, to the same extent as heat killing of plant tissues, elicited similar levels of epicormic and lignotuberous shoot growth. The root systems of the seedlings were inspected to determine whether the root tips were healthy, and selected root tips were monitored to determine if and when they had resumed growth. Survival rates of epicormic and lignotuberous shoots were enhanced by the presence of healthy leaves. The recommencement of growth after stress by the development of epicormic or lignotuberous shoots was preceded by root tip growth, which emphasises the importance of a healthy root system. Managing for the best soil conditions possible during and immediately after stress may be a key to successful shoot production and tree recovery. 1 CEU (A, U, M, T, Bs, Bm)

Callery pear (Pyrus calleryana) is a tree notorious for poor branch union and breakage during storms. Structural pruning is a pruning technique that can be practiced on young trees to strengthen tree branch attachment. Callery pear (Pyrus calleryana ‘Redspire’) was structurally pruned and allowed to grow for 7 years and compared to an unpruned control. A breaking device was used to determine branch strength by providing a static load to simulate a snow or ice load. Branches from pruned and unpruned trees were pulled to failure to observe any difference from pruning. Regardless of the structural pruning treatment, trees that were unpruned were larger in diameter at breast height (DBH) and width at the end of the test. No differences were found in testing branch union strength for either pruned or unpruned trees, suggesting that more time is needed to determine the long-term benefits of structural pruning. Branch tissue moisture content was greater than trunk tissue both in immediate post-harvest testing and in samples over time. Also, branch moisture content observations suggested the time available for field testing branch union strength could be as much as 5 to 9 days after harvest. 0.5 CEU (A, U, M, T, L, Bp)

Background: Laurel wilt disease has caused the extensive mortality of lauraceous species in the southeastern United States. The causal agent is an invasive fungus, Raffaelea lauricola, which is a symbiont of the beetle Xyleborus glabratus and causes a rapid, fatal vascular wilt. Early diagnosis of laurel wilt is imperative for efficient disease management. The current diagnostic process, however, is slow due to the lengthy laboratory procedures required to confirm pathogen presence. Methods: We tested the robustness and field-portability of a recently developed, species-specific, loop-mediated isothermal amplification (LAMP) assay for R. lauricola, with the overall goal of eliminating the need for a laboratory confirmation of the diagnosis. We tested the robustness of the assay using benchtop equipment with naturally infected samples. We then tested the assay directly in the field using a portable device. Results: The assay successfully detected R. lauricola directly from symptomatic wood tissue using crude DNA extracts. Furthermore, the assay readily allowed users to distinguish between symptoms caused by R. lauricola infection and similar symptoms caused by other agents. In-field, we assayed wood samples from symptomatic redbay (Persea borbonia [L.] Spreng) and sassafras (Sassafras albidum [Nutt.] Nees) across the Southeast and successfully detected R. lauricola-infected trees in less than an hour. Conclusion: Results of this study confirmed that the field-deployable LAMP assay is robust and can rapidly and accurately detect R. lauricola in infected trees directly on-site. LAMP technology is well suited for in-field implementation, and these results serve as an incentive for further development and use of this technology in the field of forest pathology. 0.5 CEU (A, U, M, Bs, Bp)

Unmanaged, foliar pathogens of urban trees can be detrimental to tree health and aesthetics. Overreliance on synthetic fungicides increasingly means alternative means of pathogen management are now required. The purpose of these studies was to investigate the efficacy of 3 commercially available agents, harpin protein, salicylic acid derivative, and liquid chitosan, which can initiate induced resistance (IR) in plants. IR agents were applied independently and in combination with a synthetic fungicide (boscalid + pyraclostrobin) against 2 foliar pathogens (Venturia pirina and Guignardia aesculi) under field conditions with Pyrus communis ‘Williams’ Bon Chrétien’ and horse chestnut (Aesculus hippocastanum) acting as tree hosts. These agents were tested over 3 consecutive years. In 4 of 5 field studies, the use of an IR agent alone reduced pathogen symptom severity, increased fruit/seed yield, and enhanced leaf chlorophyll content. In virtually all studies, application of boscalid + pyraclostrobin at 2/3 strength plus an IR agent provided the same degree of pathogen control as boscalid + pyraclostrobin at full strength. Application of boscalid + pyraclostrobin at 1/3 strength plus an IR agent provided a reasonable degree of foliar pathogen control. Results showed that a combined mix of an IR agent with a 1/3 reduced dose of boscalid + pyraclostrobin was as effective at reducing symptom severity of 2 foliar pathogens as boscalid + pyraclostrobin applied at full strength, provided at least 4 sprays were applied during a growing season. (A, U, M, Bs, Bp)