Growth Of Street Trees Research Articles

Large-scale determinants of street tree growth rates across an urban environment.

Urban street trees offer cities critical environmental and social benefits. In New York City (NYC), a decadal census of every street tree is conducted to help understand and manage the urban forest. However, it has previously been impossible to analyze growth of an individual tree because of uncertainty in tree location. This study overcomes this limitation using a three-step alignment process for identifying individual trees with ZIP Codes, address, and species instead of map coordinates. We estimated individual growth rates for 126,362 street trees (59 species and 19% of 2015 trees) using the difference between diameter at breast height (DBH) from the 2005 and 2015 tree censuses. The tree identification method was verified by locating and measuring the DBH of select trees and measuring a set of trees annually for over 5 years. We examined determinants of tree growth rates and explored their spatial distribution. In our newly created NYC tree growth database, fourteen species have over 1000 unique trees. The three most abundant tree species vary in growth rates; London Planetree (n = 32,056, 0.163 in/yr) grew the slowest compared to Honeylocust (n = 15,967, 0.356 in/yr), and Callery Pear (n = 15,902, 0.334 in/yr). Overall, Silver Linden was the fastest growing species (n = 1,149, 0.510 in/yr). Ordinary least squares regression that incorporated biological factors including size and the local urban form indicated that species was the major factor controlling growth rates, and tree stewardship had only a small effect. Furthermore, tree measurements by volunteer community scientists were as accurate as those made by NYC staff. Examining city wide patterns of tree growth indicates that areas with a higher Social Vulnerability Index have higher than expected growth rates. Continued efforts in street tree planting should utilize known growth rates while incorporating community voices to better provide long-term ecosystem services across NYC.

Assessing urban-heating impact on street tree growth in Berlin with open inventory and environmental data

AbstractExcess heat (i.e., Urban Heat Island; UHI) and other urban conditions affect tree physiology with outcomes from enhanced growth to mortality. Resilient urban forests in the face of climate change require species-specific understanding of growth responses. However, previous studies assessing growth dynamics were primarily based on remote sensing of communities rather than individuals, or relied on labor-intensive methods that can limit the spatial coverage necessary to account for highly variable urban growing conditions. Here, we analyze growth dynamics of common urban street tree species over time and across space for Berlin (Germany) combining dendroecological (temporal) and inventory assessments (spatial). First, we show annual increments increased across the 20th century for early (i.e., young) growth. Second, we use an approach relying on open inventory data to identify growth potential in relation to excess heat while accounting for age, potential management effects, and the urban fabric (i.e., planting area; building density, height; available soil nutrients) with generalized additive models for the ten most abundant species. Our analyses showed that younger trees may benefit from increased temperatures, while older individuals feature lower growth at greater UHI magnitudes. Furthermore, planting area as well as building density modulate growth responses to temperature. Lastly, we discuss management implications in the context of climate change mitigation, considering that younger trees are predominantly located at UHI “hot spots” and will undergo the observed age-dependent shift in temperature-growth sensitivity. By relying on increasingly available open data, our approach here is or will be transferable to other urban regions.

A Study on Street Tree Maintenance: Focusing on Suseong-gu, Daegu in South Korea

Purpose: In urban society, street trees are closely related to our lives. However, many people do not recognize the existence and necessity of street trees on ordinary days. This study investigated the changes in the growth of street trees exposed to environmental damage and artificial management due to street maintenance. This paper aims to provide necessary data for street tree management by analyzing changes in the growth of street trees according to the road size in terms of temporal change and management of street trees.
 Method: Field surveys were conducted from June to September 2021 to identify the direction of maintenance for street trees by road size. The researchers collected and analyzed data on street tree roads and basic plan data on street trees in Suseong-gu in 1997. This paper conducted One-way ANOVA by six items(tree height, root-collar diameter, crown width, diameter at breast height, degree of tree health, and degree of environmental damage). Microsoft Office Excel 2007 program and Spss Statistics 21 statistical program were used for statistical analysis.
 Results: As a result of analyzing the current state of street trees in 2021 and the change amount by road size in 1997 data, on average, the tree height increased by 5.4m, the root-collar diameter increased by 22.3cm, the crown width increased by 2.1m, and the diameter at breast height increased by 12.8cm. The degree of tree health decreased by 0.2 points, and the degree of environmental damage decreased by 1.1 points.
 Conclusion: The tree form of street trees did not have a natural tree shape due to artificial management, and street trees were damaged due to lack of management and damage from surrounding shops. The analysis results show that the appearance of street trees has grown, but street trees' growth aspects(tree health, environmental damage) have regressed due to incorrect pruning work with tall trees according to laws and ordinances. This paper suggests that street trees' species selection and improvement supplement work should be done through continuous research in the future, and systematic and efficient management should be continuously carried out for satisfaction with street trees and pedestrians.

基于街景测量的南昌市行道树结构特征与健康状况研究

行道树作为城市绿地系统的网络和骨架, 在城市居民生活中发挥着无可替代的作用。快速准确的掌握城市行道树的结构特征和健康状况, 有利于城市森林建设与管理, 进而提升其生态服务功能。基于百度街景平台, 通过街景测树法对南昌市的963个样方, 共计26727株行道树展开调查。测量内容包括行道树大小指标(树高、胸径、冠下高和冠幅)、健康状况(支架比例、枯稍比例、叶色不健康比例和死亡比例)和植被垂直结构配置情况; 并且探究了不同行政区和不同城市化强度(环城道路发展下的城乡梯度)下行道树的空间分布特征。结果表明: (1)南昌市行道树小树比例较高: 胸径在10-20 cm的占65%, 冠下高在1.5-2.5 m间的占76%, 树高在4-8 m间的占71%, 冠幅在2-6 m间的占76%;行道树生长整体表现为健康, 各指标所占比例较小, 但是叶片健康较差; 35%的样地无叶色不健康, 77%的样地无支架, 76%的样地无枯梢, 93%的样地无死亡; 植被垂直结构配置状况良好, 以乔-灌-草复合结构为主(比重为75%); (2)在空间分布上, 不同行政区行道树大小指标和垂直结构配置上差异显著、健康状况(支架比例和叶色不健康比例)均表现显著性差异(P < 0.05);不同环路行道树大小指标存在显著差异, 表现为1环>2环>3环, 垂直结构从内环到外环更为复杂, 配置等级为1环 < 2环 < 3环, 不同环路行道树健康状况(支架比例和叶色不健康比例)表现显著性差异(P < 0.05)。综上所述, 南昌市行道树整体健康状况良好, 行道树个体较小, 而且以复层结构为主, 本研究基于百度街景对南昌市行道树结构特征和健康状况进行比较全面的评价, 为南昌市今后城市行道树的规划和管理提供了基础数据支持。;As the network and skeleton of urban green space system, roadside trees play an irreplaceable role in urban residents' life. Rapid and accurate grasp of the structural characteristics and health status of urban roadside trees is conducive to the construction and management of urban forest, thus improving its ecological service function. Based on the Baidu Street View platform, this study investigated 963 quadrats, a total of 26, 727 roadside trees, in Nanchang by street view tree measurement method. Measures included indicators of street tree sizes (diameter at breast height (DBH), underbranch height (UBH), tree height (TH) and canopy size (CS)), health status (the proportion of Tripod-supporting, the proportion of Dieback, the proportion of Non-greenness leaf color and the proportion of Death trees), and vertical structure configuration of vegetation. Moreover, the spatial distribution characteristics of road trees under different administrative regions and different urbanization intensities (urban and rural gradient under the development of ring roads) were explored. The results showed that: (1) there was a high proportion of small trees in Nanchang: DBH of 10─20 cm accounted for 65%, UBH of 1.5─2.5 m accounted for 76%, TH of 4─8 m accounted for 71%, CS of 2─6 m accounted for 76%. The overall performance of the growth of street trees was healthy, the proportion of each index was small, but the leaf health was poor. In 35% of the plots, no leaf color was unhealthy, 77% of the plots had no Tripod-supporting, 76% of the plots had no Dieback and 93% of the plots had no death. The vertical structure of vegetation was in good condition, mainly composed of arbor-shrub-herb (75% of the sample land). (2) In terms of spatial distribution, there are significant differences in the sizes index and vertical structure configuration of road trees in different administrative areas, and significant differences in health status (proportion of Tripod-supporting and proportion of Non-greenness leaf color) (P < 0.05). There were urban-rural differences in the size index of road trees in different ring-road areas, which are manifested as 1^st ring > 2^nd ring > 3^rd ring, the vertical structure of the outer ring is more complex, configuration grade is 1^st ring < 2^nd ring < 3^rd ring. There were significant differences in the health status of different ring-road (proportion of Tripod-supporting and proportion of Non-greenness leaf color) (P < 0.05). To sum up, the overall health status of the roadside trees in Nanchang is good, the individual of the roadside trees is small, and they are mainly composed of multiple layers. Based on the Baidu Street View, this study makes a relatively comprehensive evaluation of the structural characteristics and health status of the roadside trees in Nanchang, which provides basic data support for the planning and management of the urban roadside trees in Nanchang in the future.

Factors influencing street tree health in constrained planting spaces: Evidence from Kyoto City, Japan

Street trees are threatened by multiple stresses from biophysical and anthropogenic factors. This situation can be extremely challenging in highly developed urban areas with limited space for tree planting. Asia has some of the most densely populated cities globally, but there is a lack of data on factors affecting street tree health in the region. This study aims to examine the impact of constrained planting environments on the health condition of street trees through a case study in Kyoto City, Japan. The health condition of 1230 street trees distributed throughout the city was assessed from June to October 2018. Additionally, several tree- and site-related variables were collected to identify their impact on tree health. Trees that were in excellent and good condition accounted for 19.9 % and 32.0 % of the sample population, respectively. Multivariate linear regression (N = 1139) revealed that tree health condition was significantly related to pruning intensity, tree pit size, adjacent land use, presence/absence of tree grate or guard, width of sidewalk, tree height, presence/absence of dedicated cycle route, tree pit pattern, crown light exposure, DBH and tree pit type. Platanus × acerifolia and other trees with large diameters exhibited relatively poor condition, along with those in tree pits with concrete paving, without tree grates, or in industrial areas, whereas trees planted in strips exceeding 1.8 m in length and exposed to weak pruning showed the best condition. These results imply the potential for healthy growth of street trees in the restricted planting spaces of Kyoto City, which suggests appropriate management and planting practices. Moreover, our empirical data can inform urban tree managers to support their efforts in making decisions on the better matching of species tolerances with urban site conditions for future street tree plans.

Growth characteristics and growth equations of the diameter at breast height using tree ring measurements of street trees in Kyoto City, Japan

Tree growth equations are indispensable for modeling tree functions for ecosystem services. However, knowledge about the growth rates of street trees in Japan remains limited. This study aimed to examine the growth characteristics of street trees (Zelkova serrata, Platanus orientalis, and Prunus yedoensis) in Japan to generate growth equations of the diameter at breast height (DBH) based on measurements of tree rings. Specifically, diameter growth was used and compared against nursery-grown trees used in previous studies in Japan and street trees in the USA. The diameter growth rate per year of Z. serrata ranged from 0.43 cm to 1.12 cm, with peak growth occurring at 17.8 years of age. For P. orientalis, the diameter growth rate per year ranged from 0.25 cm to 1.59 cm, with peak growth occurring at 7.4 years of age. For P. yedoensis, the diameter growth rate per year ranged from 0.68 cm to 1.65 cm, with no apparent peak growth. The Chapman-Richards growth function generated the best fit as a diameter growth equation for all three species out of three tested theoretical growth equations (Chapman-Richards, Gompertz, and Logistic function). For 25-year old trees, the estimated DBH of Z. serrata and P. orientalis grown as street trees was 68 % and 84 % of that of nursery-grown trees, respectively. For street trees 25 years after planting, the estimated DBH of Z. serrata, P. orientalis, and P. yedoensis in Kyoto City was 62 %, 63 %, and 56 % of that of street trees in the USA. The diameter growth of street trees in Kyoto was substantially lower than that of nursery-grown trees and street trees in the USA. Therefore, region-specific growth equations must be developed for street trees when the planting environment and management approaches are different.

Effects of varying establishment approaches on the growth of urban street trees

ABSTRACTLimited rooting space is frequently a major impediment to the growth of street trees. Different approaches to enhance the soil volume accessible to roots have been implemented in urban cities within the last decade. This survey observed the growth and health of trees planted in a) structural, load-bearing soil; b) biochar-stone-based load-bearing soil; and c) planting pits installed with structural cells. These alternative planting methods were compared against trees grown in conventional planting pits. The experimental trees were either street trees or sited within a plantation with similar soil conditions. The results indicated that tree growth and health ratings were found to be superior in the order of, planting in pits with structural cells, load-bearing material of structural soil and the biochar-stone blend, and conventional planting pits. Tree growth in structural cells was found to be 37% higher than conventional planting pits. As such, these approaches can be considered at sites where conventional pits cannot be used for tree establishment. Tree growth in pits with structural cells is therefore recommended wherever space for large planting pits is limited and when trees need to be sited close to infrastructure.

Tree pits to help mitigate runoff in dense urban areas

Tree pits are attractive stormwater control measures (SCMs) for implementation in dense urban areas because of their small footprint, their potentially low cost and the co-benefits they may bring through improved street tree growth. While they provide street trees with passive irrigation, it remains to be determined if tree pits may achieve meaningful reductions in stormwater runoff. We undertook a streetscape experiment to quantify runoff retention of tree pits in a heavy clay soil with low-rates of exfiltration. We calibrated and validated a water balance model using the field experiment data to identify tree pit characteristics driving runoff retention performance. We then applied the model to different implementation scenarios to ascertain how useful these tree pits may be at reducing runoff to return a more natural flow regime in dense urban areas. The main drivers of runoff retention were identified as exfiltration rates from the tree pits and the connected impervious catchment size. Our results show that it is possible, even in dense urban streetscapes with low conductivity (heavy-clay) soils, to achieve a 90% reduction in annual runoff and to reduce days of runoff to just 15 days per year. However, to achieve this, tree pits need to be sized between 2.5% and 8% of the impervious catchment area, depending on pit exfiltration rates. In practice, achieving these tree pit to catchment area ratios for a dense urban streetscape will require consideration in the planning stages of development works and is expected to be most feasible through implementation of tree pits alongside a suite of other complementary SCMs.

Growing on the street: Multilevel correlates of street tree growth in Montreal

Tree planting has been favoured in many North American cities, including Montreal which aims to increase its canopy from 20% to 25% in 2025. However, the mortality rate of street trees is especially high in the first few years after planting. Studies have shown that variables that are intrinsic to the tree and those related to its location, the urban form and the socio-demographic characteristics of the surrounding environment are significantly associated either with trees’ survival rate or with vegetation cover. In this research we examine variables that have statistical associations with tree growth, which is the diameter at breast height divided by the number of years on the ground, for approximately 28,000 street trees in Montreal. Independent variables were nested into three spatial scales: the tree (species and physical variables), the street section (urban form variables), and the census tract (socio-demographic variables). Multilevel models reveal that 65.51% of the growth variance is potentially explained by the species and planting physical conditions such as the east and north sides (positive associations with the growth), signage as an obstruction (negative association). 28.54% of the grow variance is potentially explained by the urban form, in our case building age (convex relationship with the growth), mixed zoning (negatively) and residential zoning (positively). At the neighbourhood level, although none of our variables is significant, 6.95% of the growth variance is be potentially explained by other missing variables. New planting programs should hence consider the urban form in order to improve tree growth.

The influence of sidewalk replacement on urban street tree growth

Interactions between tree roots and sidewalks can result in damage to sidewalks and when sidewalk damage is repaired adjacent tree roots are often severed. The objective of this study was to quantify the growth response of urban trees in restricted planting spaces pre- and post-sidewalk construction. The research included four trees species commonly planted along streets in Minneapolis and Saint Paul, Minnesota, USA. Species included were: Acer platanoides, Celtis occidentalis, Gleditsia triacanthos, and Tilia spp. Two street tree populations were sampled: trees adjacent to replaced sidewalk panels (<1.75m) and trees on streets with sidewalk construction that were greater than 3m from replaced sidewalk sections. In total, increment core samples from 292 trees were analyzed. Annual rings from each tree were measured and converted to basal area increment (BAI) for analysis. Comparisons of BAI were conducted between the two sample populations to assess differences in tree growth patterns. Pre- and post-sidewalk construction BAI was also evaluated to determine the influence of construction on growth trajectory. Growth response was quantified using resistance, resilience, and recovery indices. Species were found to differ in their response to construction disturbance. Planting space width was also found to influence post-construction growth. Tilia spp. had the highest resilience and fastest overall growth recovery post-sidewalk construction and A. platanoides exhibited the lowest resistance, resilience, and recovery post-sidewalk construction.

The effects of paving surfaces and planting orientation on street tree growth and trunk injury

The direct effects of atmospheric and re-radiated heat from surfaces surrounding a street tree can affect its establishment, growth and development through high-temperature-induced injury. Sunscald is a symptom of direct heat injury to plant tissue that occurs on the trunk and branches as a result of high solar radiation causing the dehydration and death of plant tissues. This research was designed to investigate the impact of different paving surfaces, tree orientation at the time of planting and high ambient temperatures on the establishment of roadside trees in Melbourne, Australia. Thirty young Platanus × acerifolia trees were planted along the centre median of a major road and on the west side, directly adjacent to each tree, a 0.5 m2 paved surface was installed in a timber plinth box, with a 50 mm gap between the tree trunk and plinth. Four different materials were used to surface the boxes – concrete and organic mulch (recycled wood) for which there were seven replicates and asphalt and granitic sand for which there were eight replicates. Fourteen of the trees had their north facing orientation from the nursery maintained and 16 trees were rotated 180° so that their orientation was reversed and they faced south. In the morning, mulch and asphalt were up to 2 °C hotter than concrete and granitic sand, but by late afternoon, concrete and asphalt were on average 5 °C hotter than mulch and granitic sand. The data on afternoon temperatures showed mulch and asphalt being significantly hotter than concrete and granitic sand by 10 °C or more, but by late afternoon mulch had cooled by as much as 30 °C. The asphalt remained the hottest surface throughout the day and into the evening. While not significant (p = 0.077) reversing orientation at planting appeared to interact with pavement surface to reduce shoot tip extension. This research established a relationship between the occurrence of sunscald on the trunks and poor tree growth which warrants further investigation as the Australian climate warms.

Growth of street trees in urban ecosystems: structural cells and structural soil

Samanea saman and Peltophorum pterocarpum common to the Singapore streetscape were planted in structural soil and structural cell. These were installed with the intention of observing medium to long term plant responses to the various designed soil and cell systems. To verify root colonization in these systems under the sidewalk, root presence was measured using the ground-penetrating radar (GPR) in the fifth year following installation. GPR data indicated widespread colonization of roots in the designed soil and cell system. The highest root signal counts were concentrated deeper in the profile. Trees grown in open spaces were characterized by shallow root systems. Tree physical data identified that trees grown in structural cells had significantly greater growth performances. The observations here provided evidence that these systems served as an acceptable rooting environment when confronted with limited space and soil volumes common to urban environments.

Establishment period of street trees growing in the Boston, MA metropolitan area

Slow growth following transplanting is characteristic of the establishment period, which has been studied for many years. Most of this work, however, has been conducted on trees transplanted in nurseries or favorable growing sites. In urban areas, many trees are transplanted into more challenging growing conditions, and very few studies have investigated establishment period of such trees. We analyzed ten years of transplanting records for the metropolitan Boston, MA, USA area to determine the establishment period of three species commonly planted as street trees {hedge maple [Acer campestre L.], London planetree [Platanus x acerifolia (Ait.) Willd.], and red oak [Quercus rubra L.]}. Using piecewise linear regression, we determined the “break point,” the intersection of two lines fitted to a scatter plot of caliper versus years after transplanting. The break point indicates the number of years after transplanting at which growth rate increases—the establishment period. We also analyzed whether site factors affected stem caliper. Establishment period varied among species: 2.1 years, 4.0 years, and 5.9 years for red oak, London planetree, and hedge maple, respectively. Site factors variably affected stem caliper of different species. Stem caliper of London planetree and red oak increased with greater sidewalk cut-out area. Tree grates in sidewalk cut-outs adversely affected stem caliper of London planetree. Our results can help practitioners manage street trees in the northeastern United States, but more work on trees transplanted in urban areas is necessary to understand the initial post-transplant growth of street trees.

The growth and health of street trees planted in permeable pavements

The growth and health of street trees can be limited by the amount of water available under impervious urban surfaces. Two approaches for improving the growth of street trees are the installation of permeable pavements, which allow water to infiltrate through the pavement surface and into the soil, and the integration of underlying base layers to increase the water storage capacity of the pavement system. Permeable pavements with varying depths (0, 100 or 300 mm) of underlying base layer were tested to determine whether they affected the trunk diameter, height and canopy area of broad-leaf paperbark (Melaleuca quinquenervia) trees in two soil types, sand and clay. Control trees were planted within conventional asphaltic concrete pavements without a base layer. We found that the pavement treatment effects depended on the soil type. In sandy soil, trunk diameter growth was greatest when permeable pavements were installed without a base layer. However, in clay soil, trunk diameter growth, height growth and canopy area were greatest when permeable pavements were installed with a 300-mm deep base layer. This study demonstrates that inclusion of a deep base layer may be important for maximising street tree growth when permeable pavements are installed over poorly draining soils.; ;

Seventeen years’ growth of street trees in structural soil compared with a tree lawn in New York City

In 1997, Quercus bicolor and Quercus phellos in a New York City streetscape were planted in CU-Structural Soil under a concrete sidewalk and in a tree lawn with the intention of observing long term plant response as a comparative study of an early installation of the new designed soil method. The trees have been measured nine times since the second year post-installation. We present the growth of trunk diameter, height and slenderness ratios. To verify root colonization in the structural soil under the sidewalk, tree root presence was measured using ground-penetrating radar in 2009, year 12. In the 17th year, trees in the sidewalk were similar in size with a higher level of survivorship as compared to the trees in the tree lawn. Adjusting for year of replacement in the tree lawn, model predictions for diameter of trees 15 years post-installation were no different for Q. bicolor in either the sidewalk (21.38cm) or the tree lawn (22.05cm). Q. phellos in the tree lawn were predicted to be slightly larger, 34.29cm versus 31.34cm in the sidewalk. Roots had colonized the structural soil under the sidewalk to 60cm, its full depth. This provided evidence that the structural soil medium served as an acceptable rooting environment.

A cloud-based spatial-temporal inventory for sustainable urban soil management

Spatial and temporal databases that integrate urban tree inventories and soil quality information are needed for modern-day sustainable urban forest management. The objective of this study was to demonstrate the usefulness of low-cost and widely-available technology, such as global positioning system (GPS)–enabled cameras to photo-document sites and cloud-based products and services (Google Picasa and Fusion Tables), to aid in developing sustainable street tree management programs. Google Fusion Tables provide a cloud platform to store, share and map urban tree and soil data over time using internet connected computers, tablets or mobile devices. Although indicators of urban soil quality and best methods to assess it are not yet standardized, we demonstrate here promising indicators that are both useful and easy to incorporate into spatial and temporal databases of trees managed in urban environments. By utilizing technology, we demonstrate that site-specific urban soil quality indicators can be used together with readily-available soil rating systems specific to different plant types as a means to better evaluate and manage conditions for optimal street tree growth and health.

Immobilization of Trace Metals in Contaminated Urban Soil Amended with Compost and Biochar

Urban soil amendment with organic matter can increase the steady state concentration of trace metals in urban soil. Different types of organic matter have different abilities to sorb and retain trace metals. The potential of urban soil amended with compost derived from mixed green and table waste and with maple-wood-derived biochar to retain trace metals (Cu, Zn, Cd, Pb) in the presence of de-icing salt (Na) was studied in a leaching test. Soil amended with compost retained significantly higher concentrations of Zn and Pb, as compared to soil amended with biochar, possibly due to the high cation exchange capacity of compost and its positive effect on soil pH. Indicating high ability for retaining trace metals, compost can bind contaminants originating from urban runoff water percolating through urban soil and provide a healthier medium for street tree growth.

The effect of permeable pavements with an underlying base layer on the growth and nutrient status of urban trees

Trees in urban areas increase the liveability of towns and cities but street tree growth can be constrained by the limited soil volume available for root growth and by reduced water and nutrient availability under impervious urban surfaces. An approach to improve the growth and health of street trees is the installation of permeable pavements. This study assessed whether permeable pavements with varying depths (0, 100 or 300mm) of an underlying base layer affected soil moisture, soil temperature, tree growth and leaf nutrient status when broad-leaf paperbark (Melaleuca quinquenervia) trees were planted in two soil types, sand and clay.Permeable pavements increased moisture levels in drier sandy soil but decreased moisture levels in wetter clay soil after rainfall, with the stabilising effect of the permeable pavement on moisture levels being related to the depth of the underlying base layer. Permeable pavements and their base layers also had moderating effects on soil temperature. Permeable pavement with a deep drainage layer (300mm) increased trunk diameter growth by 55%, although growth was only increased when trees were planted in clay. Permeable pavements with a shallower drainage layer (0 or 100mm) did not affect tree growth compared with trees in control asphalt pavements. However, permeable pavements without a drainage layer reduced tree height growth in clay soil by 37 to 38% compared with pavements with a 100mm or 300mm drainage layer. In contrast, permeable pavements without a drainage layer increased trunk diameter growth in sandy soil by 65% compared with permeable pavement with a 100mm drainage layer. Leaf nutrient concentrations were often unaffected by pavement design but differences in growth between treatments were associated with differences in the concentrations of some nutrients including K, Mg and S. This study demonstrated that inclusion of underlying base layers is important for tree growth when permeable pavements are installed on poorly-draining soils. Inclusion of a base layer may not be optimal for tree growth when permeable pavements are installed over freely-draining soils.

Assessing the structure and stability of street trees in Lhasa, China

Street trees can provide important environmental services to residents living in high-altitude cities. Nevertheless the performance of street trees in this unique environment is largely unknown. This article examines the impact of high-altitude environments on the growth of street trees through a case study in Lhasa, China. The structure, species composition, and health condition of street trees in Lhasa were surveyed using a representative sampling approach. The history of street tree programs and factors that affect the health of street trees was also analyzed. The results showed that there were 24 species and cultivars in 2032 sampled street trees. The street tree population in Lhasa contained a significant number of small trees, which was due to the large-scale planting program initiated in recent years. The street tree population in Lhasa was not very stable due to the uneven age distribution. The health conditions of street trees were affected by climatic factors as well as by management practices. We concluded that unfavorable environmental conditions in high-altitude cities may affect the sustainability of street tree populations to some degree but that human management of the street tree population is a more significant factor.

The Relationship Between Structural Root Depth and Vigor of Urban Trees

The prevalence of deep root systems on urban trees has been well documented, but the consequences are not well understood. The relationship between structural root depth and vigor of street trees was investigated in Greensboro, North Carolina; Snoqualmie, Washington; and Glen Ellyn, Illinois, United States. Regression analysis was used to explore the relationship between root depth and crown vigor, trunk diameter growth, and trunk condition as indicators of tree performance. The average depth of structural roots for most species was less than three centimeters. However, in 10 of the 14 species included in the study, the structural roots of 20%–60% of the individual trees were more than eight centimeters deep. Regression analysis showed a significant relationship between root depth and indicators of tree performance for Acer rubrum, Quercus bicolor, Fraxinus oxycarpa, and Tilia cordata, but no relationship was identified for other species measured. Root depth explained less than half of the reduction in tree performance of these species, however, and is apparently only one of several factors affecting the growth of street trees.