Plains cottonwood trees (Populus deltoides subsp. monilifera (Aiton) Eckenw.) occur in riparian and urban areas in semiarid regions of western United States. The amount of water necessary to maintain healthy trees while reducing water use are management objectives along the High Line Canal in Denver, Colorado, U.S. Canal-flow days, soil moisture, precipitation, cottonwood predawn leaf water potentials (ψpd) and crown dieback were measured annually from 1997–2008. Five key findings were: 1) percent soil moisture did not correlate with ψpd, 2) trees became moderately water-stressed (ψpd < -0.3 MPa) and severely water-stressed (< -0.5 MPa) 45 and 51 days after canal flow ended, respectively, 3) ψpd of water-stressed trees increased 24–48 hours after water was added, 4) only 22% of rain events of 25 mm relieved stressed conditions for seven days, and 5) yearly average autumn and growing season ψpd correlated with autumn crown dieback at low soil moisture sites (few canal-flow days), but not at moderate or high sites (more canalflow days). Trees with ψpd > -0.30 MPa generally had low crown dieback, whereas trees with ψpd < -0.50 MPa exhibited moderate or severe crown dieback. Plains cottonwoods are relatively resilient to single-year drought, and moderately stressed trees may recover and can withstand 25%–40% crown dieback if water is available the following year for >14 days. Irrigation timing and the frequency needed to minimize cottonwood future crown dieback can be obtained from autumn and growing season predawn leaf water potentials.

Abstract Monetary valuation using urban tree appraisals can be performed with formulas, a common practice in many countries. This study compares twelve parametric type formulas: Amenity Valuation of Tree and Woodlands (Helliwell), Standard Tree Evaluation Method (STEM), French Method, Italian Method, Tedesco, Norma Granada, Trunk Replacement Formula (CTLA), Burnley Method, Danish Method, Swiss Method, and two Chilean formulas used in Municipalities of Concepción, La Pintana, and Maipú (COPIMA Method), and Peñalolén Method. Formulas were then applied to 30 trees located in Santiago, Talca and Concepción, Chile.Researchers used eight appraisers divided into two groups, according to senior-level and junior-level experience. Statistical differences were determined using the Kruskal-Wallis test of non-parametric variance, while Fisher’s least significant difference test was used to identify homogeneous groups. The results show a wide dispersion of values that were high for “emblematic” trees and low for young or low-vigor trees.Formula, type of appraisers, and inter-appraiser differences formed nine, two, and three groups, respectively. The lowest-appraised trees were obtained using the Danish and French Method, while the highest values were obtained with the Burnley, Helliwell, and STEM formulas. Although there were differences in tree value according to the type of appraiser, when comparing difference among appraisers, researchers found these were not due to experience level. Given the wide range of values found, the study authors cannot recommend any specific formula(s) for assessing urban trees, as results will depend on the variables of interest used in the formulas and their intended application and use.

Abstract New residential development is most often a death sentence for the trees that stand in its way. This behavior might be altered if developers thought there was an economic value to being more selective. Unfortunately, the relationship between tree preservation and new development is not well studied. The purpose of this study was to characterize the economic value gained from the preservation of mature trees during the land development process. The study focused on six counties constituting the greater Cleveland, Ohio, U.S., real estate and land development market. A mixed quantitative and qualitative approach was used. GIS-based data and a series of hedonic models determined the value of tree canopy associated with new home sale prices from 2009 to 2011. Qualitative interviews of development and real estate professionals revealed a nuanced association of value and challenges to tree preservation during the residential land development process. Previous methods for estimating the economic value of trees were moved forward through aerial location of trees on parcels using Google Earth™ and the National Agricultural Imagery Program (NAIP) data and through the mixed-method approach. The study provided information to a state-level agency managing the state’s incentive-based smart growth program.

Urban trees are both an asset and a cost to municipalities. Past research has focused largely on the asset—quantifying and valuing the social, economic, and environmental benefits provided by trees in urban areas. Relatively fewer studies have focused on defining the appropriate level of tree care (costs or inputs) for efficiently maintaining tree health and structural integrity, and potential resulting liabilities. On 18–20 March 2015, the International Society of Arboriculture assembled a panel of research and industry experts for a research symposium and summit titled, The Costs of Not Maintaining Trees. In the weeks leading up to the summit, the Delphi technique was initiated to help build consensus on key research questions related to the economics of trees and their care. After three iterations of questions and discussion, the panel identified 14 research topics that were deemed “very important” or “important” by at least 12 of the 14 expert panelists (80% being a commonly used threshold for consensus). Results of this work are intended to help focus future research and funding efforts in arboriculture and urban forestry.

Oriental bittersweet (Celastrus orbiculatus) is an invasive, exotic, woody vine introduced to North America in the mid- to late 1800s from East Asia. This vine is problematic because it can kill trees through competition and mechanical stress, which in turn creates problems for tree care professionals in utility right-of-way and other hazard tree work. Oriental bittersweet is becoming more prevalent as a problem throughout the eastern United States. Two manipulative field experiments were conducted across the Hudson Valley in New York State to test the timing of cutting and glyphosate herbicide effects on large vine mortality. While results from the first year indicated that herbicides were needed with vine cutting to achieve high mortality rates, this was not true with second year results. Cutting vines without herbicides produce the same, high rate of mortality of oriental bittersweet vines after the second year (>90% kill) as cut-stump treatments with herbicides. It may be important that high kill of cut vines is related to large vine size, and that stumps were in forest shade. Herbicides may not be necessary to kill cut-stump methods to kill oriental bittersweet vines that have a minimum stem diameter >2–3 cm and are growing in areas where stumps are in shade.

Economic valuation of urban trees is important for their management and to ensure that such trees are maintained and protected. However, numerous models for valuing urban trees are currently available, which has led to great variation in the final price. It has also resulted in multiple models being used within the same country, thus confusing the courts. Against this background, researchers examined whether the horizontal cross-sectional area of the tree should be used as the basis for extrapolating tree replacement cost in a linear fashion. Researchers also developed a model, the Linear Index of Tree Appraisal (LITA) model, which uses tree cross-sectional area to extrapolate from a band of known prices to a base price for any desired tree size, which can then be adjusted using an appropriate factor depending on tree vitality/damage. The LITA model is easy to use and to update, does not have any limitations concerning tree species or sizes, and does not rely on subjective judgments except in assessment of tree damage. It provides a simple method for determining the replacement cost of urban trees and is thus designed to work where ‘soft’ values are sometimes difficult to justify.

Abstract Emerald ash borer (EAB),Agrilus planipennis(Coleoptera: Buprestidae), is a devastating buprestid beetle introduced to North America from Asia. Asian ash trees exhibit resistance to EAB, likely due to a shared co-evolutionary history. Resistance to one pest, however, does not necessarily confer resistance to others. Should Asian ash be highly susceptible to North American herbivores, the utility of such species for hybridization, breeding programs, and establishment in managed landscapes could be compromised. Common urban problems, such as drought stress, can increase borer attack and survival and may further complicate the search for resistant plant material. The objectives of this study were to examine the relative susceptibility of green (Fraxinus pennsylvanica) and Manchurian (F. mandshurica) ash to EAB and indigenous borers and whether that susceptibility changed with drought stress. In a common garden experiment, EAB occurred more frequently and reached higher abundances in green than Manchurian ash. The frequency and abundance of bark beetles (Curculionidae), North American native clearwing borers (Sesiidae), and longhorn beetles (Cerambycidae) were similar in the two ash species. Generation time of EAB was uniformly one year and did not depend on ash species or water stress. Although borers increased as expected in stressed trees, the relative susceptibility of green and Manchurian ash to borers did not change. The findings suggest Manchurian ash may be resistant to several classes of borers, regardless of insect geographic origin, although these conclusions should be viewed with some caution until the results can be verified in larger trees.

Pine plantations are prone to stem breakage due to high cyclic stress levels associated with hurricane force winds. Stress analytical and finite element simulation models were constructed of a representative profile of a (Sitka) Picea sitchensis tree. The profile surface stress (S) was determined due to the combined load of tree self-weight and hurricane wind speed. The results were complemented by reference to two other studies by other researchers that investigated the impact of fatigue cycles on failure (N) of pine wood and tree sway cycles to present a stem fatigue life prediction. The position of maximum surface profile stress and trunk fracture initiation location was ascertained from a non-uniform stress response. No stress uniformity along the trunk profile was observed for any wind-load case examined. The analytical model and finite element analysis of the P. sitchensis tree trunk profile revealed a statically adequate strength reserve factor of 1.4, which suggested another mode of failure was responsible. Fatigue life failure prediction was examined under cyclic and same-stress amplitude related to the hurricane wind speed of 33 m s-1. Predicted trunk fracture occurred in 2.6 hours, which dramatically reduced to two minutes with an increase in wind speed of only 1 m s-1. The calculated exposure time was similar to that recorded during Hurricane Hugo’s transit in 1989. The time-to-failure prediction obtained by the method of analysis provided in this study seemed plausible, and that the profile associated with the P. sitchensis tree would suffer trunk breakage by low cycle fatigue failure.

Two devastating insect pests have been introduced to North America and Europe – the Asian longhorned beetle (ALB) (Anoplophora glabripennis) and the citrus longhorned beetle (CLB) (Anoplophora chinensis). These two wood-boring beetles are argued to be one of the most serious threats to the tree landscape since they have a large number of host species and genera. With the aim of creating an up-to-date compilation of these hosts, a systematic review was made of the literature for information on tree species attacked and used by ALB and CLB as hosts for complete life cycle or for feeding. This review revealed that a large number of tree species and genera are liable to be attacked by ALB and CLB. However, based on the findings, the whole picture is still unclear. One reason for this is the lack of transparency in published studies regarding lists of susceptible tree species for ALB and CLB. Another factor that needs to be reported is whether a tree species supports the complete life cycle of the beetles or just feeding by adult beetles. Without this information, species possessing moderate host qualities are at risk of being incorrectly labelled as very good hosts and hence excluded as urban trees.

Images of wind-thrown trees make for dramatic news coverage. The implied message in most coverage is that strong winds and heavy rain are the cause of the tree failure. However, is the storm the only cause of the tree falling? Many other, and often bigger, trees did not fall. This feature article reviews some of the current literature relating to windthrow of trees. The size and characteristics of tree canopies have a profound influence of the forces that winds exert on tree trunks and roots systems, while the characteristics of tree root systems often determine whether trees fail during storms. The results of a site inspection suggest that there may be other factors, such as the history of the tree and the history of management practices to which the tree has been exposed, which may contribute to its failure during a storm. Site inspections of 80 wind-thrown trees from eight different genera were conducted over a period of 20 years. The inspections revealed that damage to exposed lateral roots (87.5%), the loss of descending roots (88.8%), and evidence of soil compaction at the base of the tree (65%) were often coincident with windthrow. Evidence of trenching near the trunk of the tree (58.8%) and waterlogging of the soil around the base of the tree (56.3%) were also common correlates. The literature surveyed and the results presented not only suggest where aspects of urban tree management might be improved, but may also prove helpful to arborists assessing tree hazards related to possible windthrow. Inspection protocol criteria should include damaged or decayed lateral roots, the loss of descending roots, evidence of site or trenching work close to the trunk, and whether trees are growing in compacted and waterlogged soil.