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Vegetation management is a critical component of rights-of-way (ROW) maintenance for preventing electrical outages and safety hazards resulting from tree contact with conductors during storms. Northeast Utility's (NU) transmission lines are a critical element of the nation's power grid; NU is therefore under scrutiny from federal agencies charged with protecting the electrical transmission infrastructure of the United States. We developed a decision support system to focus right-of-way maintenance and minimize the potential for a tree fall episode that disables transmission capacity across the state of Connecticut. We used field data on tree characteristics to develop a system for identifying hazard trees (HTs) in the field using limited equipment to manage Connecticut power line ROW. Results from this study indicated that the tree height-to-diameter ratio, total tree height, and live crown ratio were the key characteristics that differentiated potential risk trees (danger trees) from trees with a high probability of tree fall (HTs). Products from this research can be transferred to adaptive right-of-way management, and the methods we used have great potential for future application to other regions of the United States and elsewhere where tree failure can disrupt electrical power.

The persistence and fall rate of snags (standing dead trees) generated during bark beetle outbreaks have consequences for the behavior, effects, and suppression of potential wildfires, hazard tree and timber salvage operations, wildlife habitat, and numerous ecosystem processes. However, post-beetle snagfall dynamics are poorly understood in most forest types. We tagged standing live and dead lodgepole pine (Pinus contorta), subalpine fir (Abies lasiocarpa), and Engelmann spruce (Picea engelmannii), including beetle-killed pine snags following the peak of a recent mountain pine bark beetle outbreak in watersheds at the Fraser Experimental Forest in northcentral Colorado and sampled snagfall 10 and 12 years later. Bark beetle attacks began in 2003, peaked by 2006, and killed 78% of overstory lodgepole pine in 133 plots distributed across a range of stand and site conditions. Of those snags, only 17% fell between 2007 and 2018. Most snags broke at ground level, due to butt rot, and were oriented downhill. In contrast, snags that tipped up or snapped off above the ground were oriented with the prevailing winds. Equal numbers of snags fell singly and in multiple-tree groups, and equal numbers remained elevated rather than in contact with the ground. Lodgepole pine snagfall was 1.6-times higher on steep slopes (>40%) where dead pine density was higher, compared to flatter sites. Based on our findings and previous research, we estimate that one-half the beetlekilled lodgepole pine in high-elevation forests such as those at Fraser may fall within 15–20 yr of beetle infestation, but that some pine snags are likely to persist for decades longer. Postoutbreak snagfall dynamics create a multiple-decade legacy of bark beetle outbreaks that will persist longer in high-elevation compared to lower-elevation forests.

Fuel treatment implementation in dry forest types throughout the western United States is likely to increase in pace and scale in response to increasing incidence of large wildfires. While it is clear that properly implemented fuel treatments are effective at reducing hazardous fire potential, there are ancillary ecological effects that can impact forest resilience either positively or negatively depending on the specific elements examined, as well as treatment type, timing, and intensity. In this study, we use overstory tree growth responses, measured seven years after the most common fuel treatments, to estimate forest health. Across the five species analyzed, observed mortality and future vulnerability were consistently low in the mechanical-only treatment. Fire-only was similar to the control for all species except Douglas-fir, while mechanical-plus-fire had high observed mortality and future vulnerability for white fir and sugar pine. Given that overstory trees largely dictate the function of forests and services they provide (e.g., wildlife habitat, carbon sequestration, soil stability) these results have implications for understanding longer-term impacts of common fuel treatments on forest resilience.

Emerald ash borer ( Agrilus planipennis ) (EAB), an Asian woodboring beetle accidentally introduced in North America, has killed millions of ash ( Fraxinus spp.) trees and is spreading rapidly. This study examined the effects of tree- and site-level factors on the mortality of ash trees in stands infested by EAB in OH, USA. Our data show that ash populations in forested sites can progress from healthy to almost complete mortality of mature trees within 6 years. Although the end result of nearly complete mortality does not vary, survival analysis with 5 years of data showed that some factors affected the rate of mortality. We found more rapid mortality in stands with lower densities of ash trees. This finding supports an extension of the resource dilution hypothesis whereby concentration of EAB on few trees in low ash density areas leads to rapid decline of these trees. This contradicts an extension of the resource concentration theory that greater host density increases relative pest abundance and host mortality. Although reductions in ash density via diversification may be desirable for other silvicultural, conservation, and management objectives in preparation for EAB, our study shows that the management strategy of reducing ash density is unlikely to protect the remaining ash trees. Survival analysis also showed that mortality was more rapid for trees shaded by other trees and for trees initially exhibiting dieback. In management scenarios where hazard tree removal must be spread over several years due to budget constraints, focusing initial tree removal on stressed trees is recommended.

Street trees are valuable to urban environments, providing environmental, aesthetic, and social benefits. However, local authorities and municipalities are under pressure to cut down street trees because of concerns about fallen trees and broken branches. The problem is that this risk assessment can be done only by agronomists (experts) in some places, which is limiting. The idea is to train the local municipality’s gardeners (non-experts) to conduct risk assessments for street trees using a criteria-defined protocol developed by the Israeli Ministry of Agriculture. In our case study, we compare a risk assessment on street trees done by gardeners to a risk assessment done by an agronomist. The findings showed that most non-experts agreed with every criterion in the protocol. The strength of the relationship between the expert score and the non-experts’ average score was high and significant. Most criteria had a high or complete agreement between the gardeners and the agronomist. The visible risks criterion has a medium agreement, while the height–diameter ratio criterion has the lowest agreement between the gardeners and the agronomist. Local authorities and municipalities have room to rely on their gardeners (after a short training) to assess the risks of street trees falling when a criterion-defining assessment protocol is used.

Trees have been playing important roles in our lives for centuries; however, too often, city councils in Malaysia are unaware about the consequences of a tree failure such as property damage and personal injury. Identifying hazardous trees and taking appropriate corrective actions can protect property and save lives. A study was conducted to identify the criteria and indicators needed to identify hazardous street trees in Kuala Lumpur, Malaysia. The Delphi method was used in this study to solicit the opinion from the experts through a series of questionnaires. This study generated and identified 6 criteria and 38 indicators that arborist need to evaluate to identify hazardous street trees in Kuala Lumpur. Hopefully the generated criteria and indicators will be an initial step for Malaysian park managers as they implement their hazard tree management programs.

Tree risk is the likelihood of property damage or personal injury from a potentially hazardous tree in cities. We aimed to compare multilayer perceptron (MLP) and random forest (RF) model techniques to predict Plane trees failure hazard in urban areas. In this research, 500 Plane trees in different urban structures were selected, and 12 variables were measured for target trees prediction as model independent variables. Tree failure hazard (tree fails along next 3 yr) was modeled by two machine learning techniques: MLP and RF. The RF model represents the higher accuracy in training (100%), test (94.4%), and all data sets (98.4%). The results of variable importance calculation of designed RF model revealed that wind‐protected aspects, soil depth, length of cracks and cavities, and internal decay are the most important variables respectively that influence the classes of Plane tree failure. The urban foresters or designers can easily determine the possibility of Plane trees risk by running the designed graphical user interface and entering 12 variables of Plane tree. As a result, it will help foresters and urban area managers to make better decisions and predict the proper time to decrease harm from Plane tree failure. Core Ideas Trees failure hazard is a thread for human life and structures of cities. The multilayer perceptron (MLP) and random forest (RF) models were compared in accuracy for hazardous trees. The RF model with 94.4% accuracy was developed to assess Plane trees failure. Wind protection, soil depth, and length of cracks are influencing variables. RF is applied to rehabilitate or remove trees before any unexpected failure occurs.

The purpose of this study was to investigate the standard values of living, undamaged iron-wood (Casuarina equisetifolia) trees by different nondestructive techniques. This study also detects the transversal stress wave velocity (V) and tomogram, and resolves corresponding V maps of the trees with and without decay damage. First, a visual tree inspection form with seven categories of tree defects is proposed for tree hazard assessment. The range of demarcation between decay-damaged and sound wood occurred at an approximate V of 1461–1636 m/s by transversal stress wave velocity tomography. Different nondestructive evaluation parameters can serve as an index for diagnosing standard values (with or without decay). A positive significant relationship was found between the diameter and transversal minimum V of 2D in undamaged trees. Moreover, the product diameter × frequency of evaluated value by lateral impact vibration method tended to increase with increasing minimum V of 2D using tomography in undamaged and decay-damaged trees. Decay damage in iron-wood living trees could be inspected and detected by lateral impact vibration method and transversal stress wave velocity tomography for the general location and area of wood deterioration.

Tree assessment methodologies, currently used to evaluate the structural stability of individual urban trees, usually involve a visual analysis followed by measurements of the internal soundness of wood using various instruments that are often invasive, expensive, or inadequate for use within the urban environment. Moreover, most conventional instruments do not provide an adequate evaluation of decay that occurs in the root system. The intent of this research was to evaluate the possibility of integrating conventional tools, currently used for assessments of decay in urban trees, with the electronic nose–a new innovative tool used in diverse fields and industries for various applications such as quality control in manufacturing, environmental monitoring, medical diagnoses, and perfumery. Electronic-nose (e-nose) technologies were tested for the capability of detecting differences in volatile organic compounds (VOCs) released by wood decay fungi and wood from healthy and decayed trees. Three e-noses, based on different types of operational technologies and analytical methods, were evaluated independently (not directly compared) to determine the feasibility of detecting incipient decays in artificially-inoculated wood. All three e-nose devices were capable of discriminating between healthy and artificially-inoculated, decayed wood with high levels of precision and confidence. The LibraNose quartz microbalance (QMB) e-nose generally provided higher levels of discrimination of sample unknowns, but not necessarily more accurate or effective detection than the AromaScan A32S conducting polymer and PEN3 metal-oxide (MOS) gas sensor e-noses for identifying and distinguishing woody samples containing different agents of wood decay. However, the conducting polymer e-nose had the greater advantage for identifying unknowns from diverse woody sample types due to the associated software capability of utilizing prior-developed, application-specific reference libraries with aroma pattern-recognition and neural-net training algorithms.

Trees along railway networks represent a high risk due to their potential to fall during extreme weather events. The identification of locations along railway tracks with highest tree fall hazard is an important part of a proactive natural hazard management. A new user-friendly GIS tool (as ArcGIS toolbox) was developed that provides the opportunity to detect individual trees along railway lines and to estimate the hazard of tree fall. By an automated analysis of open source digital remote sensing data and additional open source geodata, the tool allows for an up-to-date and area-wide monitoring of trees on railway lines and other infrastructural elements. Important parameters describing meteorological conditions, site conditions, topographic conditions and tree characteristics are implemented. The tool was successfully tested and applied to two federal states in Germany (Northrhine-Westphalia and Thuringia). Due to the automatization of most of the processes, it is possible to extend the application to larger areas with low effort, i.e., to the Germany-wide rail network or to other countries. It is also possible to perform the analysis for other modes of transport. In the context of natural hazard management, the tool can be applied in prevention and can usefully support already existing vegetation management concepts.