Brian Kane

Hazard tree liability in the United States: Uncertain risks for owners and professionals

Abstract The liability United States (U.S.) tree owners face from hazardous trees on their private properties has and continues to undergo a transformation. The traditional common law legal test focused upon whether a tree owner had acted to create a hazardous condition on the property. The modern trend is towards a test that imposes greater responsibility and greater uncertainty on tree owners and arborists. Abandoning the natural/artificial distinction, the modern test, adopted in half the U.S. jurisdictions, imposes general principles of negligence on tree owners. This paper discusses the U.S. legal context for hazardous trees, particularly the impacts on individual tree owners. It closes by addressing various practical means to minimize the risks associated with the modern legal standards, both for susceptible tree owners, and for professionals assessing the subject property.

The effect of crown architecture on dynamic amplification factor of an open-grown sugar maple (Acer saccharum L.)

Tree failure may cause significant economic and societal disruptions in urban environments. A better understanding of the relationship between branches and stem as they affect the dynamic response of decurrent trees under wind loading is needed to reduce the risk of tree failure. Finite element (FE) models were used to identify the parameters that primarily impact tree response. A base model was developed using data from a sugar maple (Acer saccharum L.) located in Belchertown, MA, USA, from which parametric models were subsequently developed. Confidence in the base model was gained by comparing the natural frequency of this tree with experimental results. Results from a parametric study incorporating changes in eight different tree parameters (stem diameter, slenderness ratio of branches, number of branches, damping ratio, branch attachment heights, branch attachment angles, branch azimuth angles, and elastic modulus) are then presented to help identify critical model properties that affect the dynamic amplification factor (Rd) of the tree. A single parameter was varied in each model while keeping others unchanged from the base model. Parameters with the greatest effect on Rd included stem diameter, number and slenderness of branches in the crown, elastic modulus of stem and branches, and damping ratio. Thus, it may be possible to use pruning to alter crown architecture to reduce the risk of tree failure.Tree failure may cause significant economic and societal disruptions in urban environments. A better understanding of the relationship between branches and stem as they affect the dynamic response of decurrent trees under wind loading is needed to reduce the risk of tree failure. Finite element (FE) models were used to identify the parameters that primarily impact tree response. A base model was developed using data from a sugar maple (Acer saccharum L.) located in Belchertown, MA, USA, from which parametric models were subsequently developed. Confidence in the base model was gained by comparing the natural frequency of this tree with experimental results. Results from a parametric study incorporating changes in eight different tree parameters (stem diameter, slenderness ratio of branches, number of branches, damping ratio, branch attachment heights, branch attachment angles, branch azimuth angles, and elastic modulus) are then presented to help identify critical model properties that affect the dynamic amplification factor (Rd) of the tree. A single parameter was varied in each model while keeping others unchanged from the base model. Parameters with the greatest effect on Rd included stem diameter, number and slenderness of branches in the crown, elastic modulus of stem and branches, and damping ratio. Thus, it may be possible to use pruning to alter crown architecture to reduce the risk of tree failure.

Effects of crown structure on the sway characteristics of large decurrent trees

Key messageOur manuscript provides novel information about the sway response of large, open-grown trees, for which there are very few data. Our results contrast previous studies on conifers.AbstractOpen-grown trees in residential settings, which often assume a decurrent form, provide many benefits but also pose a risk to people and property if they fail. Reliable mechanistic models to predict failure of such trees are uncommon. Parameters to describe dynamic oscillations such as natural frequency (fn) and damping ratio (ζ) are important components of mechanistic models, but few data exist for large, open-grown trees. Attributes of crown architecture and tree size as well as fn and ζ were measured on eight large, open-grown sugar maples (Acer saccharum) growing in Belchertown, MA, USA. Although previous work has not demonstrated this correlation, fn was directly proportional to the cumulative diameter of primary branches. Similarly, previous work has not established reliable predictive models for ζ, which was directly proportional to crown width of sugar maples. Predicting fn from the cumulative diameter of primary branches is consistent with the multi-modal dynamic response of trees. Predicting ζ from crown width appeared to be due to aerodynamic damping, consistent with previous studies on broad-leaf trees.

Determining parameters related to the likelihood of failure of red oak (Quercus rubra L.) from winching tests

Key messageThis study provides data necessary to develop mechanistic models of the failure of open-grown trees. The literature contains few such data. Some results contrast previous studies on conifers.AbstractIn cities and towns, tree failure can cause damage and injury. Few studies have considered large, open-grown trees when measuring parameters related to tree failure. To measure elastic modulus and maximum bending moment and stress, we winched red oaks (Quercus rubra L.), including some with co-dominant stems and others with extant decay. To simulate decay in a subsample of trees, we cut voids in the trunk before pulling trees to failure. Maximum bending moment was greatest for uprooted trees, but maximum bending and shear stresses were greatest for trees that failed in the crown in the vicinity of branches. The likelihood of failure at a void or area of extant decay increased as the loss in area moment of inertia increased. The moduli of elasticity and rupture of specimens taken from trees were greater than values measured on the trees themselves. Failure at the union of co-dominant stems only occurred when we pulled them apart, loading them perpendicular to the plane bifurcating the union. Some of the results are inconsistent with previous work on conifers; more data on open-grown trees are necessary to develop mechanistic models to predict tree failure.

Compliance with the ANSI Z133.1 — 2006 safety standard among arborists in New England ☆

INTRODUCTION Arboriculture is hazardous work. A consensus safety standard exists, but little is known about compliance with it. This study aimed to determine whether accreditation and certification are associated with safety practices and to identify specific safety practices adhered to most and least. METHOD Sixty-three tree care companies in southern New England were directly observed on job sites. Adherence to the American National Standards for Arboricultural Operations (ANSI Z133.1 - 2006) was compared across companies that were accredited, non-accredited with certified arborists on staff, and non-accredited without certified arborists on staff. RESULTS Companies with accreditation or certified arborists demonstrated greater safety compliance than those without. However, low compliance was found across all company types for personal protective equipment (PPE) use, chain saw safety, and chipper safety. CONCLUSIONS Greater attention to PPE, chain saw, and chipper practices is warranted across the industry. Safety in non-accredited companies without certified arborists especially needs improvement. PRACTICAL APPLICATION Only partial compliance was found among accredited companies and companies with certified arborists. Intervention strategies are needed for all company types for the use of PPE and safer use of chain saws and chippers.

Loss in moment capacity of tree stems induced by decay

Key messageWe model varying decay in tree cross-sections by considering bending theory to estimate moment capacity loss (MCL) for the sections. We compare MCL with experiments on selected oak trees.AbstractTree failures can damage property and injure people, sometimes with fatal consequences. Arborists assess the likelihood of failure by examining many factors, including strength loss in the stem or branch due to decay. Current methods for assessing strength loss due to decay are limited by not accounting for offset areas of decay and assuming that the neutral axis of the cross-section corresponds to the centroidal axis. This paper considers that strength loss of a tree can be related to moment capacity loss (MCL) of the decayed tree cross-section, because tree failures are assumed to occur when induced moments exceed the moment capacity of the tree cross-section. An estimation of MCL is theoretically derived to account for offset areas of decay and for differences in properties of wood under compressive and tensile stresses. Field measurements are used to validate the theoretical approach, and predictions of loss in moment capacity are plotted for a range of scenarios of decayed stems or branches. Results show that the location and size of decay in the cross-section and relative to the direction of sway are important to determine MCL. The effect of wood properties on MCL was most evident for concentric decay and decreased as the location of decay moved to the periphery of the stem. The effect of the ratio of tensile to compressive moduli of elasticity on calculations of MCL was negligible. Practitioners are cautioned against using certain existing methods because the degree to which they over- or underestimate the likelihood of failure depended on the amount and location of decay in the cross-section.

The effect of simulated trunk splits, pruning, and cabling on sways of quercus rubra L.

Key messageCabling co-dominant stems at different heights and tensions altered neither frequency nor damping ratio, but the location and proportion of pruned crown mass significantly influenced both frequency and damping ratio.AbstractAmenity trees provide many benefits, but can damage property and injure persons. Arboricultural treatments like pruning and cabling intend to reduce the likelihood of tree failure, but the effect of such treatments on tree sways is not well known. We measured the sway response (frequency and damping ratio) of seven Quercus rubra L. before and after consecutive arboricultural treatments, including the addition a climber swaying freely or secured rigidly to the tree. We also quantified crown architecture and tree mass. Cabling two co-dominant stems did not influence sway response, but pruning increased frequency and decreased damping ratio. The effect of pruning depended on the proportion and location of pruned crown mass. Adding a climber predictably affected frequency and damping ratio in accordance with physical principles. This work adds novel insights to the understanding of tree sways, since previous studies have been limited by single trees, pruning types, or pruning severities.

Statistical modeling of tree failures during storms

Abstract The failure of trees during storms imposes strong economic and societal costs. Statistical modeling for predicting the probability of a tree failing during storms has the potential to help improve tree risk management. The purpose of this study is to explore the potential predictability of tree failure using advanced predictive modeling approach. These models also have broader applicability for modeling failures of technical systems during adverse weather events. To train and test models, we use a data set from a real case study in Massachusetts, USA. We compare the out-of-sample predictive accuracy of several machine learning models including logistic regression, classification and regression trees, multivariate adaptive regression splines, artificial neural network, naive-Bayes regression, random forest, boosting, and an ensemble model of boosting and random forest. Our results demonstrate that the ensemble model of boosting and random forest achieves the best prediction accuracy in predicting the failure probability of trees for the case study storm. Our results can help tree care professionals make better decisions to reduce the risk of tree failure prior to the storm.