Persian walnut (Juglans regia L.), which is native to Central Asia, has been widely cultivated throughout Europe over millennia as a multipurpose tree. However, only recently the naturalization process outside cultivation has been studied, mostly in temperate Europe, with no information regarding the Mediterranean region. Here we provide the first field investigations about the natural regeneration of walnut in two traditional Mediterranean agroecosystems: an irrigated mixed orchard in suburban areas and a non-irrigated prickly pear (Opuntia ficusindica [L.] Mill.) orchard. The natural regeneration densities were statistically different in the two agroecosystems, ranging from 75 individuals per hectare in the prickly pear orchard to 200 individuals per hectare in the mixed orchard. Crows were frequently observed actively carrying walnuts in both environments. The irrigation practices and the shade provided by larger trees in the mixed orchard, and the potential benefits provided by prickly pear individuals, seemed to be crucial for seedling establishment and development in the two orchards, respectively. On the other hand, climate does not seem to represent a constraint for walnut recruitment, even if the mean annual temperature at the mixed orchard is slightly above the optimal temperature for walnut. Other biotic and abiotic factors that may trigger or hamper the naturalization process are also discussed in this paper, which explores the research needs for better understanding the naturalization potential of the Persian walnut in Mediterranean agroecosystems, as well as the effects of different land uses and future climate change on this process.

We identified relationships between ecosystem services provided by trees and environmental variables, including temperature (°C at ground level and 1.5 m), relative humidity (%), particulate matter (PM10, maximum and average), noise (dBA), and ultraviolet radiation (UV at 1.5 m). This study was carried out in Talca, Chile, a mid-sized city. Measurement locations were selected in three areas based along three main avenues in the center of the city during three different seasons and three different schedules of day, generating 15,515 data in total. In circular plots, with 8 meter radiuses, measurements were recorded at the center and at a point on the perimeter. A correlation matrix was calculated and an ANOVA was conducted with canopy cover, schedule of day, and season as variation sources. The results show a high dispersion, and the correlation matrix that canopy coverage has a weak relationship with variables was studied. The results of the ANOVA showed the least number of significant differences associated with the canopy cover, schedule of day, and season, which showed significant differences for all variables. Tree coverage showed significant differences for all variables using the Tukey Test, with the exception of minimum noise. Plots with greater coverage were associated with increases in the particulate matter and relative humidity and decreases in maximum noise, temperature, and ultraviolet radiation. During mornings, the highest measurements of particulate matter, noise, and relative humidity were reported, whereas temperature maximums occurred at mid-day. The results confirm the importance of urban trees, specifically the canopy coverage, in mitigating negative environmental aspects in urban areas.

Abstract In urban areas there is a limited amount of soil space available for tree root growth. However, many systems have been developed that provide rooting space below pavement while supporting the weight of vehicles and pedestrians. Two main approaches have emerged: 1) supported pavement, and 2) structural growing media. This research was composed of two controlled studies that compare variations of these two approaches. The first was a 10-year study using elm trees that compared gravel-based structural soil (GBSS), expanded slate structural soil (ESSS), expanded slate (ES) alone, a concrete supported pavement and a compacted control. The second study was a four-year study usingLiriodendrontrees that compared GBSS, sand-based structural soil (SBSS), Silva Cells™, Stratacells™, an open control, and a compacted control. The results of these two studies showed that the trees growing in the supported pavement treatments with low-density soil media resulted in significantly greater tree growth and a healthier appearance. The treatments with the highly compacted soil media had less root development and less top growth. However, soil media that were highly compacted experienced less subsidence.

Tree survival is a performance metric for urban forestry initiatives, and an understanding of the factors that influence mortality can help managers target resources and enhance survival. Furthermore, urban tree planting investments depend on tree survival to maximize ecosystem services. In this literature review, we categorized factors commonly associated with urban tree mortality and summarized mortality rates published in 56 studies, focusing on studies of trees along streets, in yards, and in landscaped parks. Study designs included quantitative field monitoring of uneven-aged tree populations and tracking planting cohorts of even-aged trees, as well as qualitative analyses. Annual mortality rates ranged from 0.6 to 68.5% for cohort studies and 0 to 30% for repeated inventories of uneven-aged trees. The 1st, 2nd, and 3rd quartiles of annual mortality were 2.8 to 3.8%, 4.4 to 6.5%, and 7.1 to 9.3% for planting cohorts, and 1.6%, 2.3 to 2.6%, and 3.0 to 3.3% for repeated inventories of uneven-aged trees (ranges reflect studies that reported a range for the time period or mortality rate). For cohort studies, annual mortality tended to be highest during the first five years after planting. The most commonly cited biophysical factors associated with mortality were taxa (15 articles), tree size/age (13 articles), and site characteristics (12 articles). The most commonly cited human-related factors were stewardship, maintenance, and vandalism (15 articles). More long-term studies are needed to investigate how site characteristics influence mortality, including rarely examined soil and microclimate characteristics. Future research should also examine institutional structures related to mortality outcomes, as well as parcel-level sociodemographic factors and resident behaviors.

This study on investigating change in the material properties of ash trees after infestation by emerald ash borer (EAB) (Agrilus planipennis) occurred at two locations in northeast Ohio in the summer of 2013. The trees at either site were divided into three groups based on % canopy lost from EAB (group I = 0 to 5%, group II = 6 to 25%, and group III = greater than 40%). A digital image correlation (DIC) system was used to evaluate and compare strain (tissue deformation) on ash branches that were (static) loaded to failure. Stress wave transmission times (Tm) of sound waves through stem wood and fine roots and root balls of the ash trees also were assessed. The DIC evaluations revealed that branches of ash trees that were in groups II and III exhibited significantly lower strain after static loading compared to that observed for trees in group I. Analysis of stress wave Tm revealed that group III trees had significantly higher Tm times compared to the other two groups. Fine root necrosis was significantly higher in group III trees and lowest in group I trees. Extracted root balls from group III trees had significantly higher percentage decay compared to that observed from trees in groups I and II. These data provide fundamental insight into the material properties of ash trees after infestation by EAB and can contribute to arboricultural guidelines for ash tree preservation and help develop safety protocols to address structural loss in trees after EAB infestation.

The emerald ash borer (EAB) (Agrilus planipennis Fairmaire) invasion of North America has increased interest in ash (Fraxinus, Oleaceae) phylogeny, ecology, and physiology. In a common garden in central Ohio, we compared the performance of three North American ash cultivars that are highly susceptible to EAB (F. pennsylvanica ‘Patmore,’ F. americana ‘Autumn Purple,’ and F. nigra ‘Fall Gold’), one North American species that is less susceptible to EAB (F. quadrangulata), and two taxa that are resistant to EAB (F. mandshurica and F. mandshurica × F. nigra ‘Northern Treasure’). During the 2015 growing season, we measured diameter growth, foliar N concentration, specific leaf area, and on four dates (two with adequate and two with low precipitation) we measured CO2 assimilation rate (A), stomatal conductance (gs), intercellular CO2 concentration (Ci), photosynthetic nitrogen use efficiency (PNUE), variable fluorescence (Fv’/Fm’: efficiency of energy harvested by open photosystem II reaction centers), and the fraction of photons absorbed by photosystem II that were used for photosynthesis (ɸPSII). F. pennsylvanica grew fastest and on most sampling dates was superior in physiological performance (A, gs, and ɸPSII). Generally, however, there was little interspecific variation in growth and physiology among the different ash taxa tested, as all performed well. This suggests that the EAB-resistant F. mandshurica and F. mandshurica × F. nigra hybrid, as well as the moderately resistant blue ash, are as physiologically well-suited to growing conditions in the Midwestern United States as green and white ash cultivars that had been widely planted prior to the EAB invasion.

Identifying ash genotypes that are resistant to emerald ash borer (Agrilus planipennis Fairmaire) (EAB) continues to be an effort of importance to widen the existing knowledge on interspecific variation in EAB-host preference, identify mechanisms involved in EAB infestation, and aid in development of EAB-resistant ash hybrids that could potentially serve as viable replacements in urban plantations. A research plantation composed of 17 cultivars and 2 seedlings of ash trees was established in Toledo, Ohio, U.S., to monitor the susceptibility of these trees to EAB. The tree mortality was recorded on an annual basis since 2005. The results from the study and its implications, at the end of 12 years of monitoring, are presented in this paper. The study reaffirmed what is known about the resistance of the Asian ash species Fraxinus mandshurica (‘Mancana’) and the general susceptibility of North American ashes to EAB. However, it was observed that the degree of susceptibility to EAB varied across the different cultivars, with white ash cultivars ‘Autumn Purple’ and ‘Rosehill’ showing higher survival rates. However, this conclusion is based on a low replication, and all but one individual of each cultivar were infested at the end of the study. The findings suggest a need for continued and thorough screening of ash cultivars for identifying resistant genotypes.

A number of factors can influence successful street tree establishment, including inappropriate selection of stock, poorquality stock, poor planting technique, insufficient irrigation, poor weed control, and inadequate maintenance. Urban tree managers need reliable, accurate, and practical indicators of whether street trees have successfully established to inform decisions about removing supporting stakes or continuing irrigation regimes. The establishment of street trees planted as large format stock was investigated using a survey of 510 trees from 21 species managed by three municipalities in Greater Melbourne, Australia. A planted tree can only be considered established when the partial root system in the root ball or the confined root system in a container has developed into a spreading root system, utilizing moisture and available nutrients throughout a larger soil volume. Thus, an indicator of root expansion into soil of a greater volume is necessary, as are measures of canopy growth, such as shoot-tip growth or canopy dieback. The survey assessed six factors indicative of successful or poor establishment: whether trees had been planted too deeply, whether trees exhibited trunk movement at or below the soil surface, damage to the trunk, trunk sunscald injury, presence of epicormic shoots on the trunk, and whether there were co-dominant stems. The results demonstrated that trunk damage (8%) and codominant stems (5%) occurred at low rates in the trees, but the presence of epicormic shoots (12%) and sunscald damage (12.5%) was more common, and 12% of trees had been planted too deeply and 42% of trees were unstable. Three criteria—shoot tip extension, trunk movement in the ground, and percentage of canopy dieback—provided useful measures of whether street trees were assessed as being well- or poorly-established. This is the first study to record a high incidence of sunscald injury to urban trees in Australia.

Landscape professionals need target-selective insecticides for managing insect pests on flowering woody ornamentals that may be visited by bees and other insect pollinators. Chlorantraniliprole, the first anthranilic diamide insecticide registered for use in urban landscapes, selectively targets the receptors that regulate the flow of calcium to control muscle contraction in caterpillars, plant-feeding beetles, and certain other phytophagous insects. Designated a reduced- risk pesticide by the United States Environmental Protection Agency, it has a favorable toxicological and environmental profile, including very low toxicity to bees and most types of predatory and parasitic insects that contribute to pest suppression. Chlorantraniliprole has become a mainstay for managing turfgrass pests, but little has been published concerning its performance against the pests of woody ornamentals. Researchers evaluated it against pests spanning five different orders: adult Japanese beetles, evergreen bagworm, eastern tent caterpillar, bristly roseslug sawfly, hawthorn lace bug, oleander aphid, boxwood psyllid, oak lecanium scale (crawlers), and boxwood leafminer, using real-world exposure scenarios. Chlorantraniliprole’s efficacy, speed of control, and residual activity as a foliar spray for the leaf-chewing pests was as good, or better, than provided by industry standards, but sprays were ineffective against the sucking pests (lace bugs, aphids, or scales). Basal soil drenches in autumn or spring failed to systemically control boxwood psyllids or leafminers, but autumn drenches did suppress roseslug damage and Japanese beetle feeding the following year. This study indicates that chlorantraniliprole can be an effective component of integrated pest and pollinator management programs on woody ornamentals.