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Forests
Special Issues
Tree Stability and Tree Risk Analysis
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Tree Stability and Tree Risk Analysis

A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Urban Forestry".

Deadline for manuscript submissions: closed (25 April 2023) | Viewed by 41366

Special Issue Editor

Dr. Brian Kane

E-Mail Website
Guest Editor
Department of Environmental Conservation, University of Massachusetts – Amherst, 160 Holdsworth Way, Amherst, MA 01375, USA
Interests: arboricultural biomechanics; tree worker safety

Special Issue Information

Dear Colleagues,

In cities and towns, trees provide many benefits. However, because they are often near targets, such trees also present risk. Arborists and urban foresters manage tree risk to minimize costs associated with tree failure such as debris removal, economic disruption, property damage, personal injury, and litigation. Key components of managing tree risk include assessing the likelihood of failure, estimating the severity of consequences to a target if a tree failed, and determining appropriate ways to mitigate risk. Likelihood of failure depends on the loads a tree experiences and its load-bearing capacity; the severity of consequences depends on the value and occupancy rate of the target, and the size of the tree part predicted to fail; mitigation often includes arboricultural practices such as pruning and the installation of support systems. For this Special Issue, we encourage submissions related to these topics, including but not limited to empirical, theoretical, and modeling investigations of the following:

  1. Techniques to assess tree stability and likelihood of failure:
    1. Assessing loads that induce failure;
    2. Assessing load-bearing capacity (including factors that alter load-bearing capacity such as defects and response growth);
  2. Intrinsic and extrinsic factors that influence the likelihood of failure;
  3. Approaches to and techniques for risk analysis;
  4. Approaches to and techniques for risk mitigation;
  5. Risk tolerance of tree owners.

We hope that this Special Issue provides a forum for novel insights that will advance the science and practice of tree risk management.

Dr. Brian Kane
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Forests is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • arboriculture
  • likelihood of target impact
  • ikelihood of tree failure
  • pruning
  • risk mitigation
  • risk tolerance
  • severity of consequences of tree failure and impact
  • support system installation
  • tree risk analysis
  • tree risk assessment
  • tree risk evaluation
  • tree risk management
  • tree stability
  • urban forestry

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Published Papers (15 papers)

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Research

9 pages, 2018 KiB  
Communication
Do Sonic Tomography and Static Load Tests Yield Comparable Values of Load-Bearing Capacity?
by Steffen Rust and Andreas Detter
Forests 2024, 15(5), 768; https://doi.org/10.3390/f15050768 - 27 Apr 2024
Viewed by 1281
Abstract
We tested the hypothesis that the loss of load-bearing capacity, as estimated by means of static load tests and from sonic tomography, is comparable. This is of practical importance for arborists when they have to assess results reported by different consultants or when [...] Read more.
We tested the hypothesis that the loss of load-bearing capacity, as estimated by means of static load tests and from sonic tomography, is comparable. This is of practical importance for arborists when they have to assess results reported by different consultants or when they have to choose between applying one of these two methods in a specific case. A total of 59 trees, primarily Fagus sylvatica and Quercus robur, were subjected to static load tests and sonic tomography. The pulling test method yielded the residual stiffness of the stem at every position tested with a strain sensor as an intermediate quality parameter used to merely validate the actual estimations of safety against fracture. Based on the shape of the parts of the stem cross-section that are considered load bearing, sonic tomograms can be further processed in order to assess the loss of load-bearing capacity from defects like decay. We analyzed the correlation of these biomechanically equivalent parameters. This was only the case to a very limited extent. Sonic tomography and static load tests cannot replace each other, but they can complement each other. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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13 pages, 3065 KiB  
Article
Trees Adjust the Shape of Branch Unions to Increase Their Load-Bearing Capacity
by Steffen Rust
Forests 2023, 14(5), 1041; https://doi.org/10.3390/f14051041 - 18 May 2023
Viewed by 3774
Abstract
The likelihood of branch union failure often needs to be assessed in tree risk assessment. Most of the guidance used in practice is based on the shape of these forks, specifically the shape (“U” or “V”), the angle between the branches, the presence [...] Read more.
The likelihood of branch union failure often needs to be assessed in tree risk assessment. Most of the guidance used in practice is based on the shape of these forks, specifically the shape (“U” or “V”), the angle between the branches, the presence of lateral bulges, and the aspect ratio of the branches. This study extends previous studies with a novel approach to the biomechanical analysis of fork shape and contributes results from destructive tests on two important European tree species, using comparatively large trees. Surprisingly, many samples deviated from the expected pattern of constant or decreasing cross-sectional area from the trunk beyond the fork. The results show three mechanisms that counteract the potential weakening at a bifurcation, two of which have not been documented before: an increase in section modulus from the stem base to where the stems part, an increase in section modulus caused by lateral bulging, and an increase in section modulus in the branches caused by an adjusted shape. Neither the shape of the forks nor the amount of included bark had a significant impact on their strength. Like several previous studies, the results of this study caution against the use of simple rules to assess the likelihood of branch union failure. The increasing availability of “digital twins” of urban trees may help us to use these results to assess the shape of branch unions in a quantitative way. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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Graphical abstract

19 pages, 3274 KiB  
Article
Internal Decay in Landscape Oaks (Quercus spp.): Incidence, Severity, Explanatory Variables, and Estimates of Strength Loss
by Nicholas J. Brazee and Daniel C. Burcham
Forests 2023, 14(5), 978; https://doi.org/10.3390/f14050978 - 10 May 2023
Cited by 1 | Viewed by 2064
Abstract
As trees age, internal decay and the risk of stem failure become important management issues for arborists. To characterize the incidence and severity of internal decay in landscape oaks, 323 pairs of sonic and electrical resistance tomograms were generated from 186 trees, representing [...] Read more.
As trees age, internal decay and the risk of stem failure become important management issues for arborists. To characterize the incidence and severity of internal decay in landscape oaks, 323 pairs of sonic and electrical resistance tomograms were generated from 186 trees, representing five species: Q. alba, Q. bicolor, Q. palustris, Q. rubra, and Q. velutina. Overall, 135 (73%) oaks had detectable decay. When intermediate sonic velocities were included, the mean area of decay (AD) was 41% with a mean strength loss (ZLOSS) of 35%. Among all oaks, Q. rubra had the highest frequency of decay symptoms and signs of a pathogen. Binomial regression showed that diameter, symptoms, and oak species were the best predictors of decay incidence, and beta regression showed that diameter, scanning height, and species were the best predictors of decay severity. Quercus alba had the highest mean AD while Q. bicolor or Q. palustris had significantly less decay, depending on tomogram interpretation, across all modeled conditions. Despite considerable variability, the empirical model of decay incidence and severity fit to tomography measurements can inform decay assessments of landscape oaks, but the detailed tomograms allowed more precise strength loss estimates, especially for offset decay columns. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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19 pages, 6602 KiB  
Article
Effect of Geometry Precision and Load Distribution on Branch Mechanical Response
by Barbora Vojáčková, Jan Tippner, Robert Mařík, Mojtaba Hassan Vand, Thiéry Constant and Jana Dlouhá
Forests 2023, 14(5), 930; https://doi.org/10.3390/f14050930 - 30 Apr 2023
Viewed by 1542
Abstract
Tree risk assessment requires mechanical response studies, but simplification of the shape, material, or boundary conditions is necessary when dealing with such complex structures. To observe overall tree response, sub-structuring to several levels of detail can be used, enabled by recent developments in [...] Read more.
Tree risk assessment requires mechanical response studies, but simplification of the shape, material, or boundary conditions is necessary when dealing with such complex structures. To observe overall tree response, sub-structuring to several levels of detail can be used, enabled by recent developments in numerical methods and three-dimensional laser scanning (3D scan). This study aimed to determine an appropriate level of geometry and loading simplification allowed for high-order branches at the crown border, which is useful for the mechanical analysis of structured tree models. Four higher-order branches were pruned and experimentally tested by single-point loading. Beam and solid finite-element models (FEMs) were created based on measured geometric parameters and detailed 3D scans, respectively. The FEMs were used to analyze seven loading scenarios with force applied at (a) the center of gravity, (b) the top of side branches, (c) key discrete points, and (d) uniformly to the whole volume (to each finite element). Force was distributed by ratios weighted according to the mass, area, and diameter of side branches; or according to the mass of each finite element. The results showed no significant difference between the beam model and 3D scan-based model. The scenarios with finite elements’ mass-based force distribution deviated significantly from those of the other scenarios. The most simplified single-point loading caused a deviation in the deflection curve. The deviation of single-point loading in the case of the bending moment was related to force distribution ratios given by the branches architecture. Therefore, such loading simplification is not considered always appropriate. Consistency between the bending moment and branch deflection provided a representative mechanical response, recommended for further modeling of trees by sub-structuring. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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18 pages, 1736 KiB  
Article
Experimental Test of Non-Destructive Methods to Assess the Anchorage of Trees
by Andreas Detter, Steffen Rust and Oskars Krišāns
Forests 2023, 14(3), 533; https://doi.org/10.3390/f14030533 - 8 Mar 2023
Cited by 6 | Viewed by 2323
Abstract
More than 280 trees were uprooted in winching tests monitored by high resolution inclinometers at the base of the trees and a forcemeter mounted in the winching line. The dataset comprises trees growing on different urban and forest sites in Europe and North [...] Read more.
More than 280 trees were uprooted in winching tests monitored by high resolution inclinometers at the base of the trees and a forcemeter mounted in the winching line. The dataset comprises trees growing on different urban and forest sites in Europe and North America and mainly consists of fifteen widespread tree species. For the first time, a large number of trees were measured non-destructively prior to uprooting failure, as commonly practiced by consulting arborists in static load tests. With these tests, the bending moment required to cause 0.25° root plate inclination (rotational stiffness) was determined and used to predict the strength of the root system from equations described in two evaluation methods currently used in arboriculture. The predictions were tested against the measured anchorage strength, i.e., the maximum bending moment that was required to uproot the trees. Both methods delivered good estimates, which indicates that rotational stiffness at 0.25° inclination of the stem base is a suitable proxy for anchorage strength. Both equations can be considered valid for assessing the likelihood of uprooting failure, as they systematically underestimate and rarely overestimate the actual resistance to failure of a tree’s root system. As a trend, the differences between predicted and measured anchorage strength were larger for small trees, for which the resistance of the root system was overcome at larger inclination angles. While the quality of the predictions differed for species, it did not differ between sites. The angles of stem inclination at which the anchorage strength was overcome for all trees in our dataset support models for the mechanics involved in uprooting failure that previously have been described only for conifers with a shallow root system. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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20 pages, 6173 KiB  
Article
Tomographic Images Generated from Measurements in Standing Trees Using Ultrasound and Postprocessed Images: Methodological Proposals for Cutting Velocity, Interpolation Algorithm and Confusion Matrix Metrics Focusing on Image Quality
by Stella S. S. A. Palma, Mariana N. dos Reis and Raquel Gonçalves
Forests 2022, 13(11), 1935; https://doi.org/10.3390/f13111935 - 17 Nov 2022
Cited by 2 | Viewed by 1451
Abstract
Tomographic images generated by wave propagation are important in tree inspections and can be performed in an economically more accessible way using conventional equipment and postprocessed images, but improvements are necessary to increase image quality, giving greater reliability to the results. The objective [...] Read more.
Tomographic images generated by wave propagation are important in tree inspections and can be performed in an economically more accessible way using conventional equipment and postprocessed images, but improvements are necessary to increase image quality, giving greater reliability to the results. The objective of this paper was to present a methodological proposal for the definition of parameters related to image quality produced with tomography using ultrasound equipment and postprocessed images. As a case study, the methodology was applied to five trees of the species Cenostigma pluviosum DC. Gagnon & GP Lewis (Sibipiruna). A total of 1512 tomographic images were constructed from five trees to evaluate the cutting velocity, the interpolation algorithms and the filter application. The photographs of the discs were used to evaluate the theoretical wave propagation routes in the measurement grid and to compare the tomographic images using confusion matrix metrics. The application of the methodology proposed in this species allowed us to conclude that the most appropriate velocity range for cavities inference was up to 40% Vmax and for cavities supplemented with biodeterioration up to 45% Vmax; the best interpolator was the Ellipses method with compensation, with the use of a filter; and the accuracy was the most appropriate metric for evaluating image quality. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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15 pages, 1928 KiB  
Article
Comparing the Structure, Function, Value, and Risk of Managed and Unmanaged Trees along Rights-of-Way and Streets in Massachusetts
by Ryan Suttle, Brian Kane and David Bloniarz
Forests 2022, 13(10), 1602; https://doi.org/10.3390/f13101602 - 30 Sep 2022
Cited by 3 | Viewed by 1530
Abstract
Trees provide numerous benefits in urban areas, including improving stormwater retention and filtration, removing gaseous and particulate pollutants from the air, sequestering atmospheric carbon, and reducing ambient temperature. However, trees also pose risks in urban areas. Trees growing near overhead electrical utility lines [...] Read more.
Trees provide numerous benefits in urban areas, including improving stormwater retention and filtration, removing gaseous and particulate pollutants from the air, sequestering atmospheric carbon, and reducing ambient temperature. However, trees also pose risks in urban areas. Trees growing near overhead electrical utility lines cause a large proportion of electrical power outages. To mitigate this risk, arborists frequently and sometimes severely prune trees near overhead utilities for clearance and to reduce the likelihood of failure. Ostensibly, urban trees distant from utility lines are not pruned as frequently or severely. This study aimed to (i) assess factors related to both individual trees and the sample populations of trees growing near and away from overhead utility lines, and (ii) determine whether those factors differed between the two groups. In total, 200 utility easement plots and 200 non-utility control plots were distributed in Eversource Energy’s distribution territories, encompassing 2361 trees in total. Diameter at breast height (DBH), crown height and spread, percent crown missing, percent twig dieback, and likelihood of failure were gathered for each tree in the study. These variables were compared individually among study groups, and used as inputs to calculate estimated ecosystem service delivery using USFS iTree Eco v6. Overall, trees in control plots were larger and delivered more ecosystem services, per tree, than trees in utility plots. However, on a population level, trees in utility plots were more populous and delivered more aggregate ecosystem services than those in control plots. Although the aesthetics of utility tree pruning is often debated, there were no differences in likelihood of failure ratings between trees in control and utility plots. These findings may help to frame trees near overhead utility lines, commonly seen as risks or eyesores, as valuable green infrastructure and community assets. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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15 pages, 2972 KiB  
Article
Maximum Rooting Depth of Pinus thunbergii Parl. Estimated with Depth at the Center Point of Rotation in a Tree-Pulling Experiment in a Coastal Forest in Japan
by Chikage Todo, Keitaro Yamase, Hidetoshi Ikeno, Toko Tanikawa, Mizue Ohashi and Yasuhiro Hirano
Forests 2022, 13(9), 1506; https://doi.org/10.3390/f13091506 - 16 Sep 2022
Cited by 1 | Viewed by 1569
Abstract
Tree resistance to uprooting can be estimated as the critical turning moment in tree-pulling experiments. The depth at the center point of rotation (Dcp) in tree-pulling experiments is measured as an indicator of below-ground traits and is related to this critical turning moment. [...] Read more.
Tree resistance to uprooting can be estimated as the critical turning moment in tree-pulling experiments. The depth at the center point of rotation (Dcp) in tree-pulling experiments is measured as an indicator of below-ground traits and is related to this critical turning moment. However, few researchers have investigated the relationship between the Dcp and maximum root depth. Our objective in this study was to clarify whether the Dcp in tree-pulling experiments can be estimated as the maximum root depth of Pinus thunbergii Parl. in sandy soils. We also estimated which position of displacement of the center of rotation (Cp) can be applied as the Dcp. We conducted tree-pulling experiments, and compared the Dcp obtained from images with the measured maximum root depth. We found significant positive correlations between the Dcp and maximum root depth. The Cp displacement concentrated immediately below the stem when the maximum critical turning moment was reached. This position should be measured as the Dcp, which is related to the maximum root depth. We found that the Dcp can serve as a parameter, preventing the need for uprooting, when tree-pulling experiments are performed to obtain an important below-ground trait for understanding the critical turning moment. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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13 pages, 6828 KiB  
Article
Field Measurements of Tree Dynamics with Accelerometers
by Andrea Giachetti, Giacomo Zini, Yamuna Giambastiani and Gianni Bartoli
Forests 2022, 13(8), 1243; https://doi.org/10.3390/f13081243 - 5 Aug 2022
Cited by 8 | Viewed by 2102
Abstract
A comprehensive understanding of the dynamic behavior of a tree can play a key role in the tree stability analysis. Indeed, through an engineering approach, the living tree can be modeled as a mechanical system and monitored observing its dynamic properties. In the [...] Read more.
A comprehensive understanding of the dynamic behavior of a tree can play a key role in the tree stability analysis. Indeed, through an engineering approach, the living tree can be modeled as a mechanical system and monitored observing its dynamic properties. In the current work, procedures of dynamic identification used in civil engineering are applied to the case study of a black locust (Robinia pseudoacacia L.). The tree was instrumented with 13 seismic, high-sensitivity accelerometers. Time histories of the tree response under ambient vibration were recorded. Three representative sections of the trunk (the collar, the diameter at breast height, and the tree fork) were equipped with three accelerometers, in order to obtain lateral and torsional vibrations. Moreover, two pairs of accelerometers were fixed on the two main branches. The results show that it is possible to identify the natural frequencies of a tree under ambient vibrations, thanks also to the support of a preliminary finite element model. Even though the optimal position is under the tree fork, the sensors fixed at the diameter at breast height allow a clear identification of the main peaks in the frequency domain. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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11 pages, 1266 KiB  
Article
The Impact of Visual Defects and Neighboring Trees on Wind-Related Tree Failures
by Michael F. Nelson, Ryan W. Klein, Andrew K. Koeser, Shawn M. Landry and Brian Kane
Forests 2022, 13(7), 978; https://doi.org/10.3390/f13070978 - 22 Jun 2022
Cited by 12 | Viewed by 3326
Abstract
Urban trees are often more sun- and wind-exposed than their forest-grown counterparts. These environmental differences can impact how many species grow–impacting trunk taper, crown spread, branch architecture, and other aspects of tree form. Given these differences, windthrow models derived from traditional forest production [...] Read more.
Urban trees are often more sun- and wind-exposed than their forest-grown counterparts. These environmental differences can impact how many species grow–impacting trunk taper, crown spread, branch architecture, and other aspects of tree form. Given these differences, windthrow models derived from traditional forest production data sources may not be appropriate for urban forest management. Additionally, visual abnormalities historically labeled as “defects” in timber production, may not have a significant impact on tree failure potential. In this study, we look at urban tree failures associated with Hurricane Irma in Tampa, Florida, USA. We used spatial analysis to determine if patterns of failure existed among our inventoried trees. We also looked at risk assessment data to determine which visual defects were the most common and the most likely to be associated with branch or whole-tree failure. Results indicate that there was no spatial pattern associated with the observed tree failures–trees failed or withstood the storm as individuals. While some defects like decay and dead wood were associated with increased tree failure, other defects such as weak branch unions and poor branch architecture were less problematic. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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15 pages, 11566 KiB  
Article
Strength Loss Inference Due to Decay or Cavities in Tree Trunks Using Tomographic Imaging Data Applied to Equations Proposed in the Literature
by Mariana Nagle dos Reis, Raquel Gonçalves, Sérgio Brazolin and Stella Stoppa de Assis Palma
Forests 2022, 13(4), 596; https://doi.org/10.3390/f13040596 - 11 Apr 2022
Cited by 5 | Viewed by 3165
Abstract
The importance of urban forests is undeniable when considering their benefits to the environment, such as improving air quality, landscapes and breaking its monotony. However, trees are subject to failures that can cause personal and economic damage. Therefore, it is necessary to know [...] Read more.
The importance of urban forests is undeniable when considering their benefits to the environment, such as improving air quality, landscapes and breaking its monotony. However, trees are subject to failures that can cause personal and economic damage. Therefore, it is necessary to know the health conditions of the trees to define their most adequate management. Some tools are used to detect plant health conditions, such as visual analysis, tomography, and drilling resistance. In addition, some formulas based on the cavity and trunk diameter relation or the remaining trunk wall dimension are also used to infer the strength loss of a tree and its consequent risk of falling. However, these formulas have limitations, such as assuming only cavities that are always centered and not considering areas with decay. Therefore, this research evaluates whether ultrasonic tomographic imaging allows us to improve the reach of the equations proposed in the literature to infer the strength loss of trees due to the presence of cavities and decays. The results showed that ultrasonic tomographic imaging allowed the equations to be closer to real conditions of the tree trunk, such as the inclusion of wood strength reduction from decay and the displacement of internal cavities in calculating the reduction in the second moment of area. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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19 pages, 9764 KiB  
Article
Unveiling Falling Urban Trees before and during Typhoon Higos (2020): Empirical Case Study of Potential Structural Failure Using Tilt Sensor
by Karena Ka Wai Hui, Man Sing Wong, Coco Yin Tung Kwok, Hon Li, Sawaid Abbas and Janet E. Nichol
Forests 2022, 13(2), 359; https://doi.org/10.3390/f13020359 - 21 Feb 2022
Cited by 7 | Viewed by 4260
Abstract
Urban trees in a densely populated environment may pose risks to the public’s safety in terms of the potential danger of injuries and fatalities, loss of property, impacts on traffic, etc. The biological and mechanical features of urban trees may change over [...] Read more.
Urban trees in a densely populated environment may pose risks to the public’s safety in terms of the potential danger of injuries and fatalities, loss of property, impacts on traffic, etc. The biological and mechanical features of urban trees may change over time, thereby affecting the stability of the tree structure. This can be a gradual process but can also be drastic, especially after typhoons or heavy rainstorms. Trees may fall at any time with no discernible signs of failure being exhibited or detected. It is always a challenge in urban tree management to develop a preventive alert system to detect the potential failure of hazardous urban trees and hence be able to have an action plan to handle potential tree tilting or tree collapse. Few studies have considered the comparison of tree morphology to the tilt response relative to uprooting failure in urban cities. New methods involving numerical modeling and sensing technologies provide tools for an effective and deeper understanding of the interaction of root-plate movement and windstorm with the application of the tailor-made sensor. In this study, root-plate tilt variations of 889 trees with sensors installed during Typhoon Higos (2020) are investigated, especially the tilting pattern of the two trees that failed in the event. The correlation of tree response during the typhoon among all trees with tilt measurements was also evaluated. The results from two alarm levels developed in the study, i.e., Increasing Trend Alarm and Sudden Increase Alarm indicated that significant root-plate movement to wind response is species-dependent. These systems could help inform decision making to identify the problematic trees in the early stage. Through the use of smart sensors, the data collected by the alert system provides a very useful analysis of the stability of tree structure and tree health in urban tree management. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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17 pages, 16930 KiB  
Article
Reproducibility of Stress Wave and Electrical Resistivity Tomography for Tree Assessment
by Steffen Rust
Forests 2022, 13(2), 295; https://doi.org/10.3390/f13020295 - 12 Feb 2022
Cited by 4 | Viewed by 2297
Abstract
(1) Background: Tomography is widely used in tree risk assessment and forest ecology. Tomograms should be accurate, repeatable and comparable between consecutive measurements. This is the first longitudinal study addressing reproducibility over a period of several years and the key factors influencing it, [...] Read more.
(1) Background: Tomography is widely used in tree risk assessment and forest ecology. Tomograms should be accurate, repeatable and comparable between consecutive measurements. This is the first longitudinal study addressing reproducibility over a period of several years and the key factors influencing it, from raw data to final tomograms. (2) Methods: Trees were either repeatedly measured by the same researcher over periods of hours to months, by different researchers using either the same or a new installation of the same equipment, or with different tomographs. (3) Results: Overall, differences between tomograms were small and without impact on the assessment of the safety of the tree. Between initial and follow-up measurements after 2 to 5 years, the coefficients of correlation of stress wave velocity ranged from 0.75 to 0.96, those of loss in section modulus estimated from tomograms ranged from 0.82 to 0.93. The coefficient of correlation of repeated sapwood area estimates with electrical resistivity tomography was 0.97. The major cause of deviations was variation in the sensor positions between repeated tomographies, and, for electrical resistivity tomography, variation of temperature. (4) Conclusion: Provided that sensor positions are accurately recorded and documented, tomograms can reliably be repeated by different assessors over periods of years. Assessments based on complex calculations like loss of section modulus should be treated with caution, because they accumulate and amplify all sources of variation. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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13 pages, 1307 KiB  
Article
A Static Pulling Test Is a Suitable Method for Comparison of the Loading Resistance of Silver Birch (Betula pendula Roth.) between Urban and Peri-Urban Forests
by Oskars Krišāns, Linda Čakša, Roberts Matisons, Steffen Rust, Didzis Elferts, Andris Seipulis and Āris Jansons
Forests 2022, 13(1), 127; https://doi.org/10.3390/f13010127 - 16 Jan 2022
Cited by 14 | Viewed by 3122
Abstract
In urbanized areas, wind disturbances can be intensified by anthropogenic stresses under which trees may become hazardous, creating serious threats and damages to nearby targets. Therefore, species with notably lower both wood mechanical properties and compartmentalization, such as pioneers, are considered to have [...] Read more.
In urbanized areas, wind disturbances can be intensified by anthropogenic stresses under which trees may become hazardous, creating serious threats and damages to nearby targets. Therefore, species with notably lower both wood mechanical properties and compartmentalization, such as pioneers, are considered to have higher wind damage risk if subjected to unfavorable growing conditions. Eurasian aspen (Populus tremula L.) and silver birch (Betula pendula Roth.), are frequently found in both urban and peri-urban forests in Northeastern and Central parts of Europe, which strengthen the necessity for the evaluation of mechanical stability of such species. Therefore, static pulling tests were performed to compare the mechanical stability of the studied species in both urban and peri-urban forests. The loading resistance of the studied species differed, with birch being more stable than aspen, indicating aspen to be more prone to wind damage. Additionally, the mechanical stability of birch did not differ between trees growing in urban and peri-urban forests, suggesting static pulling tests are a suitable method for comparing trees from completely different growing conditions. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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11 pages, 2116 KiB  
Article
Tree Morphometric Relationships and Dynamic Elasticity Properties in Tropical Rain Tree (Samanea saman Jacq. Merr)
by Lina Karlinasari, Ulfa Adzkia, Tiara Puspitasari, Dodi Nandika, Naresworo Nugroho, Utami Dyah Syafitri and Iskandar Z. Siregar
Forests 2021, 12(12), 1711; https://doi.org/10.3390/f12121711 - 6 Dec 2021
Cited by 5 | Viewed by 4490
Abstract
Rain tree (Samanea saman) is a dominant species commonly planted as a shade tree in urban landscapes in the tropics, including in Indonesia. This species is also targeted for routine inspection and monitoring within tree management systems. Management should particularly focus [...] Read more.
Rain tree (Samanea saman) is a dominant species commonly planted as a shade tree in urban landscapes in the tropics, including in Indonesia. This species is also targeted for routine inspection and monitoring within tree management systems. Management should particularly focus on tree health through assessment of tree growth conditions as well as tree stability. However, baseline information on the relationships of many key characteristics for the rain tree (e.g., growth, morphometrics, and biomechanics) is lacking. Therefore, an investigation was carried out to determine the relationship of morphometric parameters to tree growth, which included use of an acoustic tool to assess the elasticity of the tree stem. Fifty rain trees were selected for data collection and evaluated using stress wave velocity tools and visual morphometrics assessment. The results demonstrated that, in general, the trees had good vigor and stability. Statistical analysis showed a strong relationship between tree growth parameters and selected morphometric characteristics. The use of a nondestructive acoustic-based instrument enabled determining the modulus of elasticity, which provided equivalent results with the elasticity value obtained through a common method for determining tree stability. Only live crown ratio and tree slenderness parameters had a relationship with the dynamic modulus of elasticity. These results offer a means of measurement that is simpler, less expensive, and faster than current methods, although further testing is needed for different tree species and growth sites. Full article
(This article belongs to the Special Issue Tree Stability and Tree Risk Analysis)
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