Andrew K. Koeser

Municipal tree risk assessment in the United States: Findings from a comprehensive survey of urban forest management

Awareness of tree risk assessment and management has risen in the United States in recent years. This has been prompted by publications such as the American National Standards Institute (ANSI) standard for tree risk assessment (ANSI A300 Part 9 – Tree Risk Assessment) and the accompanying International Society of Arboriculture (ISA) Tree Risk Assessment Best Management Practices, as well as the subsequent development of the ISA Tree Risk Assessment Qualification. How this increase in awareness has broadly translated into common practice in communities, is not well understood. This paper reports findings from a recent survey of urban forest operations as they directly pertain to tree risk assessment. The survey consisted of a 109-question long-form questionnaire that was sent to 1727 communities, followed up by a truncated version to non-responding communities. Six hundred and sixty-seven (38.6%) communities responded to the survey – 513 to the full survey and 154 to the truncated version. Communities that reported having a certified arborist on staff (p-value = .010), a strategic plan (p-value = .002), an updated inventory (p-value < .001), collecting risk data (p-value = .004), and having a past claim for damage or injury (p-value < .001) were more likely to regularly conduct tree risk management activities.

A review of the impact of roadway vegetation on drivers’ health and well-being and the risks associated with single-vehicle crashes

Abstract Roadside trees can help calm traffic, define roadways and reduce drivers’ stress. However, roadside trees are also one of the most common components of urban infrastructure involved in single-vehicle crashes. The aim of this review is to identify and summarise research findings on risk assessment for tree crashes and the effect of roadside vegetation on drivers’ psychology and behaviour. The literature was obtained by entering keywords into multiple search engines and tracking down references that were cited in articles that were on-point. This literature review summarises findings from road safety research, identifying trends in tree and site factors that have been used to model single car crash frequency and severity. In looking at 10 similar studies, 8 found that the location of a tree (i.e. distance from the roadway) was a significant predictor of crash likelihood or severity. Other recurring predictors of tree-related car crashes include time of day and roadway geometry (e.g. the presence of a curve). In addition, this literature review summarises findings from road safety research regarding drivers’ perception of trees in the streetscape and the impact that roadside vegetation has on drivers’ behaviour and psychology. Generally, roadside vegetation had a positive psychological effect on drivers, in that it reduced drivers’ stress and frustration, and was also correlated with reduced driving speeds.

Drivers’ risk perception of roadside trees

ABSTRACT Roadside trees can help calm traffic, define roadways, and reduce driver stress. However, roadside trees are also one of the most common components of urban infrastructure involved in single-vehicle crashes. The authors used conjoint analysis to assess driver perceptions of risk associated with roadside trees, road geometry, vehicle speed, and lighting conditions. Florida drivers were shown videos depicting street scenes with randomised variations of these four attributes and were asked to rate their perceived risk. Results indicate that drivers perceived trees in close proximity to roadways as increasing risk and night-time conditions with supplemental lighting as slightly reducing risk. Overall, lighting condition was the most important attribute driving risk ratings, followed (in order of importance) by car speed, tree proximity, and road geometry.

Growth changes of eighteen herbaceous angiosperms induced by Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in soil

ABSTRACT Study objectives were to describe and quantify growth responses (tolerance as shoot and root biomass accumulation) to soil-applied Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) treatments of eighteen terrestrial, herbaceous, angiospermous species and also; to determine how much of RDX, RDX transformation products, total N and RDX-derived N accumulated in the foliage. RDX altered growth of eighteen plant species or cultivars at levels of 100, 500, and 1,000 mg kg−1dry soil in a 75-d greenhouse study. Sixteen species or cultivars exhibited growth inhibition while two were stimulated in growth by RDX. A maximum amount of foliar RDX in a subset of three plant species was 36.0 mg per plant in Coronilla varia. Foliar concentrations of transformation products of RDX were low relative to RDX in the subset of three species. The proportion of RDX-N with respect to total N was constant, suggesting that foliar RDX transformation did not explain differences in tolerance. There was a δ 15N shift towards that of synthetic RDX in foliage of the three species at a level of 1,000 mg kg−1 RDX, proportional in magnitude to uptake of N from RDX and tolerance ranking.Reddened leaf margins for treated Sida spinosa indicate the potential of this species as a biosensor for RDX.

Estimating conductive sapwood area in diffuse and ring porous trees with electronic resistance tomography

Accurately estimating sapwood area is essential for modelling whole-tree or stand-scale transpiration from point-flow sap-flux observations. In this study, we tested the validity of electrical resistance tomography (ERT) to locate the sapwood-heartwood (SW/HW) interface for two ring porous (Quercus nigra L. and Quercus virginiana Mill.) and one diffuse porous (Acer rubrum L.) species. Estimates derived from the ERT analyses were compared with the SW/HW interface measured following dye perfusion testing. The ERT results revealed spatial variation in electrical resistance, with higher resistivity in the inner part of the cross sections. Regression analyses showed that ERT was able to accurately account for 97% and 80% of the variation in sapwood area (calculated as R2) for Q. virginiana (n = 19) and Q. nigra (n = 7), respectively, and 56% of the variation in the diffuse porous species (n = 8). Root mean square error (RMSE) values for sapwood areas of the ring porous species were 11.12 cm2 (19%) and 25.98 cm2 (33%) for Q. virginiana and Q. nigra, respectively. Sapwood area estimates for diffuse wood carried greater error (RMSE = 33.52 cm2 (131%)). Model bias for all sapwood area estimates was negative, suggesting that ERT had a tendency to overestimate sapwood areas. Electrical resistance tomography proved to be a significant predictor of sapwood area in the three investigated species, although it was more reliable for ring porous wood. In addition to the results, a comprehensive code sequence for use with R statistical software is provided, so that other investigators may follow the same method.

Nitrogen Fertility Island Stability around Prosopis glandulosa Sprouts after Mechanical Shrub Control in a Degraded Grassland

ABSTRACT We examined the effects of mechanical chopping to reduce shrub cover for grassland restoration in a semi-desert environment near Douglas, Arizona, USA. Specifically, soils were sampled to determine spatial and treatment differences, after 10 years, in soil-N fertility islands associated with undisturbed honey mesquite shrubs (Prosopis glandulosa Torr. var. glandulosa) compared with resprouted mesquite shrubs. Honey mesquite is the dominant shrub of this degraded grassland community. One decade after mechanical crushing of shrubs for grassland restoration, soil amino sugar nitrogen (N) values and patterns for resprouted honey mesquite and undisturbed shrubs did not differ from one another according to a repeated measures analysis of variance. However, the concentrations in samples of the surficial 30-cm of soil around undisturbed and resprouted shrubs combined differed statistically at 161 parts per million (ppm) at trunk, 100 ppm midway between trunk and dripline, 78 ppm at the dripline, and 46 ppm beyond the dripline. The results indicate that soil N fertility remained stable, but with decreasing levels at regular, radial sample points extending from the trunk to beyond the dripline, around mesquite shrubs that resprouted 10 years after mechanical crushing of tops for grassland restoration.

Enhancing Establishment of White Oak and American Hazelnut Enrichment Plants in a Mesic Forest Using Understory Removal and Group Selection

In the absence of periodic disturbance, primarily fire, many oak-dominated woodlands in the Eastern and Midwestern United States are transitioning to sugar maple (Acer saccharum) dominated communities. This experiment was conducted to determine the effects of forest overstory and/or understory removals on enrichment plantings of white oak (Quercus alba) and American hazelnut (Corylus americana). The combination of prescribed forest canopy openings and understory tree removal significantly increased mean twig elongation, an indicator of overall growth and vigor, of white oak as compared to control trees. A similar pattern was seen in the hazelnut, with the two treatments that included a group selection opening offering a significant growth advantage over the treatment which only included understory clearing. Group selection openings in this study were small (250 m2) compared to previously recommended canopy openings of 1,000 m2 or more, suggesting that oak and hazelnut regeneration may be enhanced without the dramatic visual impact of more intense silvicultural practices of clearcutting and shelterwood and when using large planting stock (> 1.5 m in height or 2.5 cm caliper for oak and 3–4 year old containerized hazelnut). As such, successful oak and hazelnut establishment and growth may be possible in intensively managed, frequently visited forest preserves where maintaining site aesthetics is a high priority.