Abstract Background Urban forests may be vulnerable in a changing climate, and a perceived or real lack of biodiversity may exacerbate this vulnerability. Methods We assessed the biodiversity and climate vulnerability of street trees in 5 local government areas in Greater Melbourne, Australia, along a climate gradient in old (pre-2005) and new suburbs. Results Despite significant variations in mean annual rainfall and aridity index across the study area, all locations maintained moderate to high biodiversity scores according to both Shannon and Simpson indices. Areas of higher rainfall showed strong genera dominance and a lower taxonomic richness than drier areas, yet they achieved high Simpson diversity scores, suggesting an even distribution among species within dominant genera. Newer suburbs had a lower taxonomic richness of species, genera, and families compared to older suburbs and lower Shannon and Simpson indices; no area complied with the Santamour 10/20/30 rule. Climate vulnerability assessment using climate envelope models indicated that species vulnerability did not differ along the climate gradient and that species in most locations were not very vulnerable under most scenarios. However, trees in new suburbs were less climate vulnerable compared to trees in old suburbs under the 2090 climate scenario. This difference between old and new suburbs indicates that species selection practices may have increased climate resilience, though this comes at the cost of lower overall species diversity. Conclusion While climate change poses significant challenges, our research demonstrates that considered species selection and management strategies can help create urban forests better adapted to future conditions.
Abstract Background Dutch elm disease (DED) has reshaped the American elm ( Ulmus americana ) component in North American landscapes for nearly a century. Although breeding and selection programs have produced a small number of commercially available DED-resistant cultivars, uncertainty remains regarding the durability of their resistance under current pathogen virulence. Methods This study presents a conceptual framework for screening and interpreting DED resistance based on historical breeding programs and long-term field studies. The framework was applied in a case study evaluating 3 commercially available American elm cultivars (‘Valley Forge’, ‘Jefferson’, and ‘Lewis & Clark’ [Prairie Expedition ® ]) inoculated with a locally derived isolate of Ophiostoma novo-ulmi ssp. americana in Minnesota. Trees were challenged with 3 inoculum concentrations, and resistance was assessed with 2 tree ages. Results All cultivars exhibited low wilt severity one year after inoculation across all inoculum concentrations. No significant effects of cultivar, inoculum concentration, tree age, or their interactions were detected, indicating stable resistance across the tested doses and age range. Conclusions These results are consistent with long-term North American and European studies showing that DED resistance in elm is quantitative and best expressed as functional survival or having the ability to limit pathogen spread, recover from localized wilt, and maintain canopy vigor over time. The conceptual framework and experimental results presented support the continued deployment and evaluation of DED-resistant American elm cultivars for urban and landscape restoration.
Abstract Background Residential damage from trees results in millions of dollars in insurance claims each year. In turn, insurance carriers have been increasingly forcing homeowners to prune or remove their yard trees for risk mitigation. Reduction of risk may or may not occur; however, the removal of tree canopy reduces the ecosystem benefits provided by trees. Methods Our research employed a homeowner survey in the Southeastern United States to understand and describe influences on homeowners’ tree-related risk perceptions and subsequent decisions regarding their trees using a pilot tree risk perception scale. Results Most respondents and their neighbors were influenced by their insurance carrier to prune or remove trees. Higher levels of tree-related risk perception significantly correlated with trust and satisfaction in their insurance. Respondents who had local insurance agents and personal relationships with their agents were significantly more concerned about tree risk than others. Tree-related risk perception negatively correlated with average tree canopy cover in the participants’ zip code. Conclusions The study informs arborists and insurance carriers of the factors affecting homeowners’ tree-related risk perceptions and will therefore aid in policies and practices regarding mitigation and communication of the risks involved with privately owned trees. In the context of climate change, improved communication between these industries—both of which impact the community’s tree canopy—will become increasingly necessary to mitigate natural hazard-related risks to human health and safety while maintaining ecosystem services.
Abstract Background Electric utilities spend billions of dollars annually clearing trees around power lines, while vegetation remains the leading cause of power outages at many utilities. Limited research exists to determine the cause of most power outages due to trees, particularly distribution-level outages. Methods A team of utility urban foresters at a Mid-Atlantic electric utility in Virginia, USA, investigated over 1,104 outages caused by tree failures to identify characteristics of failed trees. Using an observational retrospective case series approach, data from afflicted (naturally fallen) trees directly involved in power outages were collected on a mobile phone application for each individual outage, including tree type (hardwood, softwood), genus, size (both diameter and height), tree defects and health status prior to the failure, and the type of failure—root, stem, or branch. After exclusion of incomplete or duplicated records, statistical tests on 844 outages evaluated simple associations using Chi-square and Cochran-Mantel-Haenszel (CMH) test, as well as probabilities using multiple (more than one factor), polytomous (more than two levels of response), nominal (categorical response levels), and logistic regression, with the main objective to identify factors associated with frequency of failed tree parts. Results This study found that most tree-caused power outages (TCOs) were the result of live trees failing at the trunk, and 46% of the failures had no visible defect prior to failure. While hardwood trees had more branch failures than softwood trees, overall, there was a low likelihood of branch failures. Some hardwood species were more likely than others to have branch failure; specifically, yellow poplar and maple, while pines were less likely, which was unexpected. Defects prior to failure were observed in only half of TCOs; however, of all trunk failures ( n = 450), dead trees were 47.11%. Conclusions This study highlights the importance of implementing the Utility Tree Risk Assessment Best Management Practices (BMPs) and expanding on existing methods to identify trees with either an elevated likelihood of failure and/or likelihood of impact. Purposefully managing an urban forest at a landscape scale requires knowledge of the species composition, size class, and how trees react to biological and physical factors in the environment.
Abstract Urban land development often leads to compacted and degraded soils, hindering urban tree establishment and growth and related ecosystem services. Thus, there is a growing interest in restoring degraded soils through various urban soil management practices (USMPs). However, the impact of different USMPs on soil properties, tree establishment and growth, and ecosystem services has not been comprehensively documented and evaluated. To address this knowledge gap, we conducted a literature review, and 41 peer-reviewed articles were selected from 5,913 articles for this analysis. The key response variables included soil bulk density, soil pH, tree growth, total soil carbon, and soil infiltration rates. Existing USMPs were grouped into 4 main categories: (1) organic matter amendments; (2) organic matter with tillage/subsoiling; (3) organic matter with vegetation; and (4) vegetation alone. Urban soil research is unevenly distributed globally, with more than half (53.7%) of studies in the United States, and most studies (82.8%) were short term (≤ 4 years). Generally, USMPs improved soil properties and enhanced tree growth and ecosystem services by reducing 28% to 51% soil bulk density and increasing nutrient availability, microbial activities, infiltration rates, tree growth, and total soil carbon. These findings provide valuable insights on restoring degraded urban soils, sustaining/increasing urban tree canopy cover, and enhancing urban sustainability for urban foresters/planners, policy- and decision-makers, and researchers.
