A rapid urban site index for assessing the quality of street tree planting sites

Urban trees experience site-induced stress and this leads to reduced growth and health. A site assessment tool would be useful for urban forest managers to better match species tolerances and site qualities, and to assess the efficacy of soil management actions. Toward this goal, a rapid urban site index (RUSI) model was created and tested for its ability to predict urban tree performance. The RUSI model is field-based assessment tool that scores 15 parameters in approximately five minutes. This research was conducted in eight cities throughout the Midwest and Northeast USA to test the efficacy of the RUSI model. The RUSI model accurately predicted urban tree health and growth metrics (P < 0.0001; R² 0.18–0.40). While the RUSI model did not accurately predict mean diameter growth, it was significantly correlated with recent diameter growth. Certain parameters in the RUSI model, such as estimated rooting area, soil structure and aggregate stability appeared to be more important than other parameters, such as growing degree days. Minimal improvements in the RUSI model were achieved by adding soil laboratory analyses. Field assessments in the RUSI model were significantly correlated with similar laboratory analyses. Other users may be able to use the RUSI model to assess urban tree planting sites (<5 min per site and no laboratory analyses fee), but training will be required to accurately utilize the model. Future work on the RUSI model will include developing training modules and testing across a wider geographic area with more urban tree species and urban sites.     

Interactive effects of biochar and N-fixing companion plants on growth and physiology of Acer saccharinum

The use of biochar with N-fixing species has been shown to enhance productivity of agricultural systems, both in N-fixing crops, as well as in mixed-species systems. Here we investigate the potential for the use of a granulated mixed conifer biochar and a sugar maple biochar in combination with N-fixing companion plants in an urban forestry context. A factorial greenhouse experiment compared growth responses in silver maple (Acer saccharinum L.) saplings planted with two biochar types as soil amendments, alone and in combination with two N-fixing plant companions (Trifolium repens L. and Dalea purpurea Vent.). Both biochar types enhanced tree growth; however, a maple feedstock biochar resulted in greater increases than a granulated conifer-feedstock biochar. N-fixing companion species also increased tree growth, although the faster-growing Trifolium reduced soil moisture content and reduced sapling growth in the absence of biochar. The highest tree growth performance and total N uptake was obtained with a combination of both biochar and N-fixing plants, with a ~30 % increase in biomass compared to controls for the granulated conifer biochar, and a ~55 % increase for the maple biochar. We conclude that biochar additions in combination with N-fixing companion species have considerable promise in an urban forestry context, but that optimization of the system in terms of biochar type and species combination is an important consideration.     

Porous-permeable pavements promote growth and establishment and modify root depth distribution of Platanus × acerifolia (Aiton) Willd. in simulated urban tree pits

In dense urban areas with heavy pedestrian traffic, current trends favor covering tree pits with porous-permeable pavement over installing grates or leaving the soil exposed. However, pavement cover potentially modifies soil moisture and temperature, altering tree growth and overall resilience, especially when coupled with heat stress and drought in a changing climate. This study evaluated the response of newly planted London plane (Platanus × acerifolia ‘Bloodgood’) trees to porous-permeable resin-bound gravel pavement and associated alterations in soil water distribution and temperature, in two distinct physiographic regions in Virginia, USA. Simulated urban tree pits were either covered with porous-permeable pavement or left unpaved, and root growth and depth, soil water content and temperature, and tree stem diameter measured over two growing seasons. At both sites, trees in paved tree pits grew larger than trees without pavement. Stem diameters were 29% greater at the Mountain site and 51% greater at the Coastal Plain site, as were tree heights (19% and 38% greater), and above ground dry biomass (67% and 185% greater). Roots under pavement developed faster and shallower, with many visible surface roots. In contrast, unpaved tree pits had almost no visible surface roots, and at the Mountain site only occupied an average area of 7 cm² within the 1-m² tree pits, compared with 366 cm² in paved tree pits. Pavement may have extended the root growing season by as much as 14 days, as the average soil temperature for the month of October was 1.1 °C and 1.2 °C higher under pavement than in unpaved pits. Porous-permeable pavement installations in tree pits accelerated establishment and increased growth of transplanted trees, but may result in shallower root systems that can damage pavement and other infrastructure. In addition, shallow root systems may prevent water extraction from deeper soils, compromising drought resilience.     

Estimated nitrogen use efficiency,surplus, and partitioning in young apple trees grown in varied organic production systems

A certified organic apple (Malus × domestica Borkh.) orchard was established to study the interaction of ground cover management systems (GMS) and nutrient sources (NS) on nitrogen (N) use efficiency and N surplus in the Southern U.S. for three years. Trees treated with green compost (GC) and wood chips (WC), regardless of the NS, had greater N accumulation and leaf N use efficiency compared to the shredded paper or mow-and-blow treated trees. The WC-treated trees had comparably low N surplus relative to the GC trees that induced more [NO₃⁻] in soil or soil solution in the rooting zone in September in year 3. GC trees had the highest [NO₃⁻] mineralization in the soil during winter. GMS had greater overall effects on the tree response variables than did the NS.     

Seasonal trends in hydraulic conductance of field-grown ‘Valencia’ organge trees

Leaf water potential (ψ₁), whole tree transpiration (F) and leaf surface conductance (g), together with a number of environmental parameters, were measured from early summer until late winter in a well-watered mature ‘Valencia’ orange (Citrus sinensis (L.) Osb.) orchard during the growing season of 1977/78. F and g showed a seasonal trend, with maximum values reached during the late summer. Tree conductance (C_tree), calculated as the ratio between transpiration and the water potential difference between the wet soil and the sunlit leaves, was found to vary seasonally and showed maximum values during late summer. The soil temperature (T_s) showed a seasonal trend similar to C_tree. Analysis of this and other data from the literature confirmed that the sensitivity of tree conductance to soil temperature is related to the climatic origin of the plant species.The linear regression fitted to the relationship between C_tree and T_s was used to calculate soil temperature at apparent zero C_tree. This datum can be used as an index of plant sensitivity to root medium temperature.     

Non-destructive method for above-ground biomass estimation of Fraxinus uhdei (Wenz.) Lingelsh in an urban forest

One of the limiting factors to estimate accurately the biomass stocks of urban forests is the availability of allometric models developed from urban trees measurements. In addition, the traditional methods (destructive) to develop biomass equations are rarely applied in cities. The aim of this study was to develop a non-destructive method based on fractal analysis for trees of Fraxinus uhdei present in the green areas of Chapultepec Park in Mexico City. Diameter at breast height (DBH), total height and the height of the whorls of 46 randomly-selected trees were measured. In each tree, three different-order branches were collected to measure their total length and that of their links, the diameter before and after each branching point, the insertion angle, the number of branches, twigs and leaves, and fresh and dry weight. The felling of seven individuals at the site was taken advantage of to fit a taper function for the trunk and determine its biomass. Acceptable estimates with good accuracy were obtained for F. uhdei trees with a DBH of less than 23 cm. It is feasible to develop biomass models from measuring the branches and the trunk of young F. uhdei trees through the implementation of structural indices based on fractal geometry and without the need to fell healthy trees.     

A study of chemical characteristics of soil in relation to street trees status in Riga (Latvia)

The chemical composition of soil and appropriate supply of nutrients are very important factors for normal plant growth and development. Lime tree (Tilia x vulgaris H.), is a popular tree species used for urban landscaping in Europe. However, there is little information on the chemical element concentrations available to and recommended for T. x vulgaris in urban soils. The objectives of this study were: (1) to investigate the amount of nutrients, de-icing salts and heavy metals available for uptake by trees in the city centre on a seasonal scale; and (2) to assess the relationship between the vitality of T. x vulgaris and soil chemistry. The research was carried out in five streets and a park in Riga (Latvia) during 2005–2007. Plant-available concentrations of 17 nutrients and heavy metals were determined via 1 M HCl extraction. Soil Cl content, pH, and electrical conductivity were also measured.The investigation revealed a high heterogeneity in soil chemical composition. In total, the element concentrations in urban soils did not exceed values commonly found in urban environments. Higher concentrations of Na, Cl, Ca, Mg, Zn, Cu, and increased pH, but lower P and B concentrations were found in the street soils in comparison to the park soil. Significantly higher concentrations of Na, Cl, and Mg, and lower concentrations of K, Fe, Cu, and B, as well as unfavourable ratios of several element concentrations were found in the soils where more damaged street trees were growing. In addition, the recommended fertilization regimes are discussed.     

Trees in planters – Growth,structure and ecosystem services of Platanus x hispanica and Tilia cordata and their reaction to soil drought

Urban environments are often characterized by extensive paved surfaces, exacerbating the urban heat island effect. At the same time, limited root space due to underground infrastructure poses a challenge for planting new trees in these areas. Trees in planters have emerged as popular design elements, offering innovative and sustainable greening solutions, particularly in urban environments with limited rooting space. However, growing conditions in planters may strongly impact tree growth and the provision of environmental ecosystem services (ES). In this 3-year study, we analyzed tree growth and ecosystem services (cooling by shading, CO₂-fixation) of London plane (Platanus x hispanica Münchh.) and small-leaved lime (Tilia cordata Mill.) in four planting treatments: in-ground (G), planters in the ground (PG), non-insulated plastic planters (P), and insulated planters (PI). We also recorded soil temperature throughout the experiment and implemented soil drought conditions by reducing soil irrigation for half of the trees after one year. Our findings revealed higher thermal fluctuations in soil temperature within non-insulated plastic planters (P), reaching a maximum of 45 °C, surpassing the critical temperature threshold for plant growth (>38 °C). In contrast, insulated planters (PI) effectively mitigated soil temperatures, staying below 33.8 °C. When planted in the ground (G), P. x hispanica exhibited a significantly higher stem diameter increment (52–66%) compared to other planting treatments, aligning with the provision of ecosystem services. However, T. cordata trees showed a more moderate response to planting treatments in terms of growth and ecosystem service provision. Furthermore, the implementation of soil drought conditions resulted in a reduction of up to 34% in stem diameter increment for P. x hispanica and up to 25% for T. cordata. Our results underscore the necessity of tree species-specific knowledge about growth responses to different planting treatments for effective urban planning perspectives, as the provision of ecosystem services may be influenced differently.     

Growth and stability of deep planted red maple and northern red oak trees and the efficacy of root collar excavations

Trees with root systems established well below grade due to deep planting or soil disturbance are common in urban landscapes, yet the long term effects of buried trunks and subsequent remediation strategies, such as root collar excavation are poorly documented. We evaluated the consequences of deep planting over a 10-year period on tree growth and stability, with and without root collar excavation, for red maple [Acer rubrum L. Red Sunset^® (‘Franksred’)] and Northern red oak (Quercus rubra L.) planted at grade or 30-cm below grade. Sleeves to prevent soil-trunk contact were installed around trunks on a subset of deep trees. Root collar excavations were made during the 6th growing season for both species and trees were grown for an additional 4 and 3 growing seasons for red maples and Northern red oaks, respectively. Within two weeks of root collar excavations, pulling tests compared the effect of treatments on stability of red maples. Deep planting generally slowed growth of red maple but had no clear effect on Northern red oak. Root collar excavation had no lasting effect on growth of either species. Approximately 55% of deep red maples and 33% of deep Northern red oaks had roots crossing and in intimate contact with buried trunks, suggesting a potential for future girdling roots. Approximately 25% of deep maples had substantial adventitious rooting. All deep Northern red oaks had new roots emerging just above the first original structural roots but none were clearly adventitious. Trunk sleeves had no effect on growth for either species. Neither deep planting nor root collar excavation resulted in a loss of tree stability compared to trees planted at grade, although failure patterns varied among treatments. Overall, the biggest long term concern for deep-planted trees is the potential for girdling root formation.     

Potential climate change impacts on green infrastructure vegetation

This study investigated the impacts of successive simulated droughts and floods on two plant species (Carex lurida and Liriope muscari) commonly installed in green-infrastructure (GI) sites built in the urban northeast USA. The instantaneous stomatal conductance, and belowground biomass growth (in a second drought experiment only) were used as metrics, since they are indicators of the ability of plants to provide ecosystem functions such as transpiration and carbon uptake. The results indicate that both species have greater tolerance for floods than for droughts. Signs of stress were only evident after a simulated flood exceeding the duration of 95% of all storms that occurred in this geographic region between 1950 and 2000. By contrast, simulated droughts had a more pronounced effect on both the instantaneous conductance measures during drought and the recovery following the cessation of drought in both species. Liriope subjected to drought treatments were all able to recover and to re-establish stomatal conductance levels similar to those displayed by a control group even after repeated drought treatments. By contrast, Carex showed reduced recovery after multiple droughts, in two separate rounds of experiments. However, regardless of moisture conditions and treatment, Carex generally displayed higher stomatal conductance than Liriope, indicating greater transpiration, and CO₂ uptake than Liriope. The belowground biomass results supported this finding, i.e. Carex gained more belowground biomass than Liriope during all experiments. At the end of the experiment, the Carex subjected to drought had less than one sixth the belowground biomass of the control treatment, whereas for Liriope this ratio was only 50% (drought to control). The drought treatments, therefore, reduced the biomass of Carex more than it did Liriope, when compared to the respective control plants. Nonetheless, both species survived repeated cycles of droughts and floods, suggesting that these particular species are both likely suitable for use in GI facilities, despite projected future increases in the frequency and intensity of floods and droughts in this geographic region. From a practical perspective, the results suggest no need for irrigation or potential replacement of plants in GI systems in a changed climate.     

How good are containerized trees for urban cooling?

The capacity of urban trees in mitigating urban heat is well-known. As space is often limited, one feasible option for increasing the urban green would be containerized plants. Nevertheless, for optimizing the vitality and benefits, detailed knowledge on tree growth reactions in different types of containers is missing. We designed an experiment with two commonly planted but ecologically contrasting urban tree species Tilia cordata and Platanus x hispanica planted into the ground and in containers according to four different planting types, with or without drought stress. Along with the meteorological variables, continuous soil moisture and temperature at 25 cm depth, sap flow, as well as measurements of leaf physiological responses i.e. stomatal conductance, mid-day leaf water potential and chlorophyll content were measured three times on sunny and warm summer days during 2020 and 2021. P. hispanica showed more than double diameter increment at breast height in the ground than in containers; however, the growth trend was relatively better for T. cordata in containers. While comparing different container types and species reactions, it was clear that soil temperature within the plastic containers were significantly higher, whereas insulation is not enough to reduce either the temperature or slowing down the soil drying out. Where both the species showed lower stomatal control over atmospheric demand, P. hispanica showed leaf transpiration energy loss of around 300 W m⁻² when planted in the ground and T. cordata trees around 260 W m⁻² when planted in non-insulated containers, which are comparable to the energy loss from the street trees. Therefore, a strategy of mixed planting with faster growing species such as P. hispanica that provide stronger cooling at the initial stage in the containers to be complemented and eventually replaced with medium growing species T. cordata for relatively longer time period could be suggested.     

微生物菌剂和生根粉对甜瓜产量和土壤生态效应的影响

以甜瓜为试材,采用田间小区试验,探讨了微生物菌剂和生根粉对棚室甜瓜生理代谢、产量、土壤生态效应的影响,以期为甜瓜安全高效施肥提供参考依据。结果表明:施用微生物菌剂和生根粉可以显著提高甜瓜植株生理代谢能力和果实产量(P<0.05)。其中净光合速率提高39.92%～59.88%,蒸腾速率提高39.76%～46.18%,产量提高6.96%～31.53%。此外,施用微生物菌剂和生根粉可以改善土壤酸碱度,提高微生物数量。同时可以提升土壤酶活性,活化土壤速效磷、钾养分。     

Estimating primary productivity of forested wetland communities in different hydrologic landscapes

Five forested wetland sites in western Kentucky with hydrologic regimes varying from seasonally to continuously flooded were investigated for net above-ground biomass productivity (litterfall plus biomass growth) and for possible indicators of that productivity, including abiotic (flooding frequency and depth, phosphorus concentrations in water and sediments) and biotic (biomass, tree density, basal area, structural complexity, and mean height) indices. Net biomass productivity ranged from 205 g m^-2y^-1 for a stagnant semipermanently flooded Taxodium swamp to 1,334 g m^-2y^-1 in a bottomland forest along the Ohio River. Productivity was highest in wetlands with pulsing hydroperiods, intermediate with slowly flowing systems, and lowest with stagnant conditions. Surface water flooding of the wetlands during the growing season ranged from 17 to 100 percent of the year and did not predict productivity. Phosphorus concentrations in water and in sediments were not correlated to one another and did not, by themselves, predict productivity. No single abiotic variable predicted the exact ranking of productivity of the sites. Of the biotic variables, average tree diameter was inversely related to productivity.     

Structural response of black locust (Robinia pseudoacacia L.) and small-leaved lime (Tilia cordata Mill.) to varying urban environments analyzed by terrestrial laser scanning: Implications for ecological functions and services

Quantitative measurements of structure and morphology of urban trees are hardly exhausted so far, especially in regard to variations caused by altering urban environments. However, structure and functions of trees are heavily interwoven. In fact, knowledge about structural attributes is essential for a better understanding of urban ecosystem functions and services. In order to scrutinize spatially explicit and detailed structural attributes under varying urban environments, we acquired terrestrial laser scans and applied the according methodological approaches to the common urban tree species black locust (Robinia pseudoacacia L.) and small-leaved lime (Tilia cordata Mill.). We analyzed 52 small-leaved limes and 41 black locust trees within the city of Munich (Germany). Species as well as growing location had a significant effect on the height-diameter relation. We also found greater crown volumes for small-leaved lime. Black locust however, displayed more crown projection area and likely more shade efficient crown shapes at similar volumes. Stem inclination of black locust was found to be higher in parks than in street canyons with town squares lying in between. Furthermore, black locust displayed strong crown asymmetry in park areas, likely caused by competition with neighbors. The angles of main branches did not differ significantly between both species nor between the growing location. Branch angles, branch bending, the length of the branches as well as species and growing location had a significant effect on vertical crown center position, i.e. general crown shape. Surface complexity of lime is lower than of black locust, with its lowest manifestation in parks. Fractal-like crown surface structures, increasing surface roughness and complexity, were found to be more pronounced for black locust than for small-leaved lime. Thereby, black locust featured the highest crown surface complexity in parks, the lowest in street canyons. The results suggest that studies on spatially explicit tree structures may contribute to more target oriented tree plantings and thus, more effective exploitation of ecosystem services and benefits.     

Growth response of Ficus benjamina to limited soil volume and soil dilution in a skeletal soil container study

The interactive effects of rooting volume and nutrient availability in a skeletal soil medium designed to meet street tree and pavement needs were observed in a containerized experiment. Benjamin fig (Ficus benjamina L.) was grown in a stone-soil blended skeletal soil material (CU-Soil™) and compared to a loam soil. The same topsoil used as the soil component in the skeletal soil material was used as the sole component in the comparison soil-only treatment.Plants grown in the skeletal soil material had reduced leaf tissue N content and depressed growth compared with plants grown in non-diluted soil. No other mineral deficiencies were found. Leaf number, chlorophyll concentration, shoot weight, and root characteristics were all affected.Reduced growth from soil dilution could be offset by the provision of an enlarged rooting volume for root development. Large containers of skeletal soil were observed to have smaller root systems compared to equivalent net volumes of loam soil at the first two harvest dates of the study. By the end of the study, the large containers of skeletal soil were observed to have developed larger root systems compared to equivalent net volumes of loam soil; resulting in comparable leaf N levels and total plant dry matter. Plants in skeletal soil had lower shoot: root ratios at the end of the study. Investing resources to further root growth in times of nutrient shortages is a probable plant reaction as evidenced by differences in specific root length between treatments. The study allowed a method for directly partitioning the containerization effect by having equivalent amounts of soil over two volumes.     

Variations in leaf litter decomposition explain invasion success of Broussonetia papyrifera over confamilial non-invasive Morus alba in urban habitats

In urban environments, anthropogenic influences play an important role in determining the distribution of woody flora and consequently, the propagation of woody invaders. Land-use changes and disturbances associated with urbanization may intensify different invasive aspects of a species. Studying the extent by which invasive species vary from non-invasive species can strengthen our understanding of urban invasions. In this study, we compared leaf litter decomposition between two confamilial exotics, an invasive Broussonetia papyrifera, and a non-invasive Morus alba (both belonging to family Moraceae), growing in urban habitats. Senescent leaves of both the species and soil were collected from five study sites in Chandigarh, India. Litterbags filled with 10 g leaves each were placed in pots containing the soil collected from respective study sites. Mass remaining, decomposition constant, and soil elemental composition were determined after periodic harvesting of the pots. Decomposition was completed within 180 days in B. papyrifera and 330 days in M. alba. Initially, the decomposition rate was low in B. papyrifera; however, a rapid degradation occurred after 90 days. Species, time, and their interaction significantly affected most of the elements in soil, whereas the effect of habitat was not significant. The faster decomposition rate in B. papyrifera may result in greater turnover of nutrients over a shorter time span, thereby, favoring its colonization in the invaded regions. The difference in litter decomposition process explains the invasion success of B. papyrifera over its confamilial species, M. alba, in urban habitats.     

Effects of air temperature,soil temperature and soil moisture on growth and development of tomato itself and grafted on its own and egg-plant rootstock

The problem was studied whether tomatoes, grown in a hot and arid climate, benefit from grafting on egg-plant, which is highly efficient in water uptake. Growth and development of tomato (T), tomato grafted on its own rootstock ($\text{T}\text{T}$) and tomato grafted on egg-plant rootstock ($\text{T}\text{E}$) were compared at air temperatures of 28°C during the day and 18°C during the night ($\text{28}\text{18}$) and at 28°C constantly ($\text{28}\text{28}$), at soil temperatures of 14, 21 and 28°C with the following soil moisture regimes: wet (W₁), medium (W₂) and dry (W₃).At $\text{28}\text{18}$ and $\text{28}\text{28}$ water consumption was about equal, but the transpiration ratio at $\text{28}\text{28}$ was twice as high as that at $\text{28}\text{18}$. The latter conditions gave a much stronger plant with more fruits. At a soil temperature of 14°C water use was strongly reduced. The transpiration ratio increased with the soil temperature. Differences in plant type were small. At the highest soil temperature of 28°C fruit growth was strongly reduced. At lower soil moisture levels less water was used and the transpiration was lower. Plant type was correlated herewith.Vegetative growth of $\text{T}\text{T}$ was weaker than of T, but generative growth was stimulated. The strong E rootstock stimulated vegetative growth at high air and soil temperature, but fruit growth was very poor under these conditions; at a low soil temperature of 14°C vegetative growth was also reduced.The hope that the E rootstock would be beneficial for fruit growth at high temperatures was not fulfilled.An additional experiment in a growth-room at 23°C showed that under conditions of moisture stress there was no difference in water potential between leaves of $\text{T}\text{T}$ and $\text{T}\text{E}$.     

Allometric equations for estimating the aboveground volume of five common urban street tree species in Daegu,Korea

Quantifying urban tree biomass and carbon (C) storage by using allometric equations is required for various studies such as assessing the inventory, modelling, and measuring ecosystem services of urban trees. However, the lack of urban-specific allometric equations leads to uncertainty when estimating urban tree biomass and C storage. Therefore, we followed a nondestructive approach and developed allometric equations specifically for Acer buergerianum Miq., Ginkgo biloba L., Platanus orientalis L., Prunus yedoensis Matsum., and Zelkova serrata (Thunb.) Makino in Daegu, Korea. Diameter at breast height (DBH)-based and DBH-and-height-based allometric equations were highly accurate at estimating the aboveground volume (R² > 0.92), while the allometric equations for P. orientalis and Z. serrata developed for traditional forests overestimated volume by 68% and 427%, respectively. The addition of a height variable into the DBH-based allometric equations did not increase the reliability of the allometric equations at a local level. The mean aboveground C storage of urban street trees was 24.9 Mg C/ha except for P. orientalis with a mean of 69.7 Mg C/ha, and the total aboveground C storage of urban street trees in Daegu was 10.6 Gg C. Alternatively, a generalized allometric equation which compiled species-specific equations can be applied for large-scale estimation. The generalized equations developed in this study and those found in the literature may suggest a constant value (～2.3–2.4) for the scaling exponent in the generalized equations. Allometric equations developed from natural or artificial stands may overestimate the volume of urban street trees; therefore, estimating urban tree biomass and C storage requires urban-specific allometric equations.     

Effect of urbanization and climate change in the rooting zone on the growth and physiology of Pyrus calleryana

It is well known that trees can reduce the urban heat island and adapt our cities to climate change through evapotranspiration. However, the effects of urbanization and anticipated climate change in the soil–root rhizosphere have not been widely investigated. The current study studied the growth and physiology of the urban tree Pyrus calleryana grown in a factorial experiment with or without urbanization and simulated climate change between April 2010 and December 2012 in the Botanical Grounds of the University of Manchester, UK. The study indicated that urbanization and simulated climate change had small but contrasting effects on tree growth and morphology. Urbanization increased tree growth by 20–30%, but did not affect leaf area index (LAI) and showed reduced peak water loss and hence evapotranspirational cooling. Although soil moisture content in the upper 20 cm was higher in the urbanized plots, urbanization showed reduced sap flux density, reduced chlorophyll a:b and delayed recovery of chlorophyll fluorescence (Fv:Fm) throughout the experimental period. In contrast, simulated climate change had no effect on growth but increased LAI by 10%. Despite being more water stressed, trees grown in simulated climate change plots lost more water both according to porometry and sap flow measurements. Simulated climate change increased peak energy and water loss by around 13%, with trees having an average sap flux density of around 170 g cm^?2 d^?1, 40% higher than trees grown in control plots. Our study suggested that transpirational cooling benefit might be enhanced with a longer growth season and higher soil temperature in places such as Manchester, UK in future, but potentially at the expense of photosynthesis and carbon gain.     

Preliminary observations of the effect of spacing on the apple root system

The weight and distribution of the roots of 6-year-old apple trees ‘Cox/M.9’ with potential rooting areas of 2.2 m² (close spaced) and 17.8 m² (wide spaced) are described. Excavation and soil coring gave a similar picture of the root systems. At the close spacing, the weight of roots per tree was reduced but their density in the soil was both greater and more uniform, both surface and deep soil being better exploited.