Arboriculture & Urban Forestry

Arboriculture & Urban Forestry quizzes are available free online to members for one year after the date of publication; a maximum of six quizzes are available at any time. CEU quizzes for older articles may be purchased by both members and non-members.

Achieving the urban tree trifecta will require collaboration among municipal departments and the development of a range of public and private initiatives, but it has the potential to maximize nature-based solutions in cities facing rapid shifts due to densification and climate change. In order to ensure that urban forests are both resilient to threats and confer the maximum possible benefits, we must be able to project decades into the future in order to understand the implications of current urban forestry decisions. This study outlines a framework for creating urban-forest scenario models and reports the results of a case study conducted to highlight the ways in which decisions made at each stage of the scenario-development process impact its outcomes and application. Our case study focused on a neighbourhood in Vancouver, Canada, that is simultaneously undergoing urban densification and aiming to significantly increase canopy cover by 2050. Our study demonstrates that a salubrious, resilient, and diverse urban forest can be created via a strategic program that complements extant trees in the public domain with planting programs along blue-green streets and on private property. 1 CEU (A, U, M, T, Bs, Bm)

Arboriculture & Urban Forestry quizzes are available free online to members for one year after the date of publication; a maximum of six quizzes are available at any time. CEU quizzes for older articles may be purchased by both members and non-members.

Laurel wilt is a lethal disease of American Lauraceae caused by Harringtonia lauricola. Propiconazole is a systemic fungicide which arrests fungal growth among a variety of plant hosts. Propiconazole as a preventive treatment against laurel wilt in sassafras (Sassafras albidum) has not been evaluated. We treated sassafras trees with propiconazole using the Arborjet QUIK-jet® Micro-Injection™ and TREE I.V. Micro-Infusion™ systems (Arborjet, Inc., Woburn, MA, USA) and challenged trees by inoculating them with H. lauricola. Out of 7 trees treated using the QUIK-jet Micro-Injection system, 6 (86%) survived 52 or more weeks following inoculation with H. lauricola, while only 11% of inoculated control trees (1 of 9) survived over this period. All trees not damaged by hurricanes (n = 13) treated with propiconazole using the TREE I.V. Micro-Infusion system survived significantly longer than untreated control trees after inoculation with H. lauricola; 10 of 13 trees (77%) survived with < 50% crown loss, and 8 of 13 trees (62%) appeared entirely healthy 54 weeks post-inoculation. In the TREE I.V. Micro-Infusion system trial, 15 of 19 control trees (79%) had either died or lost ≥ 50% of living crown 54 weeks post-inoculation with H. lauricola. Results indicate sassafras trees treated with propiconazole using the Arborjet QUIK-jet Micro-Injection and TREE I.V. Micro-Infusion systems are significantly less likely to die within one year of infection with H. lauricola; however some trees may exhibit significant crown decline (≥ 50%) over this period. 1 CEU (A, U, M, Bp)

Background: Arboricultural tree climbing is inherently dangerous, in part because of the possibility of failure of the tie-in point (TIP). To help climbing arborists choose TIPs wisely, we have conducted several studies to quantify the magnitude and frequency of loading associated with arboricultural tree climbing. One parameter that has not been previously studied is whether the choice of climbing line influences loads experienced by a TIP as a climbing arborist ascends. Methods: The lead author conducted trials in which he ascended to 3 TIPs (in different trees) using 2 ascent techniques and 3 different climbing lines. During each trial, we measured loads at the TIP, and from the resulting time histories analyzed the magnitude and frequency of loading. We compared the effect of ascent technique, climbing line, and their interaction on the magnitude and frequency of loading. Results: During trials, the magnitude of loading varied between 1.1 and 1.5 times the lead author’s weight and did not differ between ascent techniques, climbing lines, or their interaction. Loading frequency varied among ascent techniques, but not climbing lines. Footlocking induced loads at a wide range of frequencies, but 2 distinct frequencies were associated with ropewalking. Conclusion: Climbing arborists can use the results of this and our previous studies to help select a suitable TIP. It is important for climbing arborists to understand the magnitude of forces associated with ascending into and working in a tree. Future studies should investigate the load-bearing capacity of a TIP from the ground. 1 CEU (A, U, M, T, L, Bp)

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)