Rainfall interception of three trees in Oakland,California

A rainfall interception study was conducted in Oakland, California to determine the partitioning of rainfall and the chemical composition of precipitation, throughfall, and stemflow. Rainfall interception measurements were conducted on a gingko (Ginkgo biloba) (13.5 m tall deciduous tree), sweet gum (Liquidambar styraciflua) (8.8 m tall deciduous), and lemon tree (Citrus limon) (2.9 m tall broadleaf evergreen). The lemon, ginkgo, and sweet gum intercepted 27.0%, 25.2% and 14.3% of gross precipitation, respectively. The lemon tree was most effective because it retained its foliage year-round, storing more winter rainfall than the leafless ginkgo and sweet gum trees. Stemflow was more important for the leafless sweet gum. Because of its excurrent growth habit and smooth bark, 4.1% of annual rainfall flowed to the ground as stemflow, compared to less than 2.1% for the lemon and 1.0% for the ginkgo. Water samples were collected from throughfall, stemflow, and a nearby control site to measure concentrations of nutrients and heavy metals. Compared to the control, samples from under trees had higher concentrations of nutrients and metals (e.g., N, P, K, Zn and Cr), indicating that atmospheric deposition to tree crowns was a major source of pollutants. Nutrient and metal concentrations were highest in gingko tree’s throughfall. Its rough stem surfaces and dense branching pattern appeared to trap more pollutions than the other two trees.     

Canopy precipitation interception in urban forests in relation to stand structure

Urban forests provide important ecosystem services. In terms of hydrological benefits, forest ecosystems in urban environments represent qualitative and quantitative filter for rainwater. We quantified the canopy interception in relation to urban forest stand structure and rainfall intensity in an urban transect of the mixed (upland) forest in the city centre, towards a riparian pine forest and a floodplain hardwood forest in the City of Ljubljana, Slovenia. Bulk precipitation in open areas and throughfall were measured with fixed rainfall collectors in each forest. Stemflow was estimated from a review of relevant literature. We found that canopy interception in selected urban forests was mainly affected by tree species composition and other stand structure variables, such as canopy cover and tree dimensions. Average annual canopy interception was highest in the mixed forest (18.0% of bulk precipitation), while the riparian pine forest had the lowest level (3.9% of bulk precipitation) and the floodplain hardwood forest had the intermediate level for interception (7.1% of bulk precipitation). The mixed forest exhibited the stand structure factors that contributed to the highest canopy interception among the studied forests: high assemblage of dominant coniferous trees, denser canopy cover and the highest growing stock. Furthermore, rainfall intensity has proven to be an important factor for the seasonal partitioning (comparing the leafed and leafless period) of canopy interception. A better understanding of precipitation interception processes in urban forests is needed to assist urban forest managing and planning, aiming at maximizing canopy interception for the mitigation of stormwater runoff and flooding in urbanized watershed.     

Rainfall interception capacity of tree species used in urban afforestation

Afforestation is inserted in the urban environment and interferes directly in the surface runoff. In order to quantify the rainfall interception by tree species, an experiment was carried out in the city of Uruaçu, Goiás, Brazil, with the four most common tree species in the urban afforestation of the region. The species chosen were the Mangifera indica (mango tree), the Caesalpinia peltophoroides (sibipiruna tree), the Pachira aquatica (munguba tree) and the Licania tomentosa (oiti). In order to register precipitation, ten pluviographs were used. They are capable of measuring precipitation over time in terms of duration, volume, and intensity. For events with a mean cumulative precipitation of 16.7 mm, the mean values of interception found in each species were: Mangifera indica - 8.0 mm; Pachira aquatica - 7.4 mm; Licania tomentosa - 7.2 mm; and Caesalpinia peltophoroides - 4.8 mm. The research confirms the importance of studies related to the identification of the species’ individual characteristics that interfere in the rainfall interception capacity and that can consequently contribute to urban drainage actions. In addition, it proves the existence of variations of rainfall interception in relation to rainfall events and during their occurrences and emphasizes the need for a careful definition of the species that will compose the urban afforestation.     

Franklin Park: 150 years of changing design,disturbance, and impact on tree growth

Urban stresses are known to affect street trees growing in spatially restricted conditions, but even in relatively large parks the cumulative effects by construction, pedestrian uses, and impacts from temporary events may have deleterious long-term effects on plant health. In Columbus, Ohio, the 93 ac (42.3 ha) Franklin Park has been subjected to major construction events and site re-configuration about once per generation—at least six times in 150 years. The first recorded shade- and ornamental tree installations occurred between 1895 and 1910. Those trees, as well as those native to the park, were mapped in 1939, 1989, and again in 2000. Testing the hypothesis that cumulative disturbance reduces tree vigor and growth rate even in open-grown conditions, tree diameters were compared over the sixty year period between 1939 and 2000. Soil compaction and percolation were measured on a 50 m grid, and maps were overlain to determine where site disturbance,buildings, utility lines, paths and pavements had occurred since 1860. Only 8% of the park's surface escaped disturbance; undisturbed areas occurred only in isolated patches. For all trees, trunk diameter increase averaged 0.5 cm/year for 61 years. While late successional species (e.g., Quercus, Acer) had growth rates less than expected for open-grown specimens, many early successional species (Celtis, Populus) were less affected. Despite availability of soil nutrients and lack of canopy or understory competition, tree health was generally poor in all size classes and the majority of the trees present in 1939 were in decline by 2000.     

BOOK REVIEWS

Abstract

ADOPTION WISDOM: A GUIDE TO THE ISSUES AND FEELINGS OF ADOPTION. Russell, Marlou. Santa Monica, CA: Broken Branch Productions, 1996, 204 pp., ISBN 1-888511-12-5, $14.95 paper. Reviewed by Tracy Simonson.

CHILDREN IN LONG-TERM FOSTER CARE: EMOTIONAL AND SOCIAL DEVELOPMENT. McAuley, Colette. Aldershot: Avebury, 1996, 196 pp., ISBN 1-85972-252-0, $59.95 hardcover. Reviewed by Karen Schmid.     

Modelling changes in dimensions,health status,and arboricultural implications for urban trees

Canberra, the capital of Australia since 1911, has been developed into a modern city from its original site on a nearly treeless plain. Today the city has about 300,000 inhabitants and 500,000 trees. The authors were requested by the managers of the urban public tree resource to survey their asset and to develop a computer-based system that would aid them in anticipating future maintenance requirements and its costs. This paper reports on our response. We have surveyed 3,000 streets and parks in the city, noting the species, number, and condition of every public space tree. We have also obtained the dimensions of sample trees, noting their total height, maximum crown width, height of maximum crown width, diameter at maximum crown width, and height at crown break. A management system has been developed using Microsoft Access^TM.Using standard regression techniques available on the package JMP^TM, we found that total tree height was related to age for all species and that all other parameters of interest were related to height or transformed values of height. We assumed a sigmoidal growth curve and calibrated 114 height/age curves to cover the 165,000 trees of the 340 species we have in our database. As well we used the data on tree condition to determine the rate at which populations change from healthy to stressed.By interviewing foremen and supervisors we were able to determine the maintenance treatments carried out in Canberra, the equipment used, and the number of trees that can be treated in a day, for each type of operation.The management system can be used to display the current inventory for each street or park, by suburb, in the database. It can also be used to model future increases in size or crown condition, to predict the operations that will be required as a consequence of tree growth or crown deterioration, and finally, by applying multipliers to equipment and personnel, to estimate the future costs of tree maintenance. Managers can use the system to anticipate problems such as uneven expenditure requirements in future years.     

Urban channel incision and stream flow subsidies have contrasting effects on the water status of riparian trees

The water relations of riparian trees are often closely tied to stream hydrology and channel morphology, which can be altered by urban development. In regions with limited precipitation, urban water use can generate or augment dry-season stream flows, potentially providing a water subsidy to riparian trees. However, urbanization is also associated with high storm flows that cause stream channel incision, or downcutting, which could limit the effect of flow subsidies by lowering riparian water tables. We investigated the effects of urban dry-season flow subsidies and stream channel incision on the water status of streamside trees in Sacramento, California, which has a Mediterranean climate with a distinct and lengthy dry season. For two common facultative riparian species, Quercus lobata (valley oak) and Fraxinus latifolia (Oregon ash), we analyzed both midday stem water potential (Ψ_stem) measurements and leaf carbon isotope signatures (?¹³C) to determine whether channel incision and dry-season flow had interacting effects on seasonal midday water stress and longer-term water use efficiency. We found that stream flow could substantially reduce dry-season water stress in both tree species, but only at low levels of channel incision. Leaf ?¹³C signatures for Q. lobata suggested increased water use efficiency in trees growing along incised streams and those lacking dry-season flow. Urban management decisions that affect both dry-season base flows and channel incision can thus influence the growth and health of riparian trees, potentially leading to broader changes in riparian ecosystems.

     

Energy balance and transpiration in an urban tree hedgerow in Mexico City

A series of sap flow (transpiration, TRP) and energy balance components measurements were carried out in a representative tree hedgerow of Fraxinus uhdei in Mexico City (19° 19' N, 99° 11' W, 2250 m ASL). Measurements of sap flow in the trunks of the trees was selected as an alternative tool instead of eddy covariance or Bowen ratio-energy balance methods in order to determine the energy balance components of the tree canopy. These measurements were made in October (end of the rainy season) and December (dry season) in 1997, from 8:00 to 17:00 LST. TRP showed a unimodal pattern during the day. Mean daily transpiration was higher at the end of the rainy season (1506 g m^–2 d^–1) than in the begining of the dry season (972 g m^–2 d^–1) with maxima rates of 0.075 and 0.046 g m^–2 s^–1, respectively. During the rainy season net radiation (Q_N) was mainly dissipated by latent (Q_E) and sensible (Q_H) heat, 60 and 34 %, respectively. Latent heat increased in the day up to 184 W m^–2. Q_N was dissipated by Q_H and Q_E by 75 and 25%, respectively, and Q_H had a maximum hourly value of 298 W m^–2 during the day (8:00-17:00 LST) in the dry season. Seasonal differences in Q_E and Q_H were probably due to differences of water availability. Heat storage of the tree hedgerow canopy was found to be a negligible component of the energy balance in both seasons. Actual transpiration of the system was always lower than transpiration at equilibrium. This was probably due to a low water availability in the substratum, a high atmospheric evaporative demand and an effective stomatal control. Because the tree hedgerow was completely surrounded by paved areas and wind was coming from a drier side, it is possible that transpiration rates were affected by advection probably supressing TRP.     

Environmental and crown related factors affecting street tree transpiration in Helsinki,Finland

We investigated the drivers of street tree transpiration in boreal conditions, in order to better understand tree water use in the context of urban tree planning and stormwater management. Two streets built in Helsinki in 2002, hemiboreal zone that had been planted either with Tilia?×?vulgaris or Alnus glutinosa f. pyramidalis were used as the study sites. Tree water use was measured from sap flow over the 2008–2011 period by the heat dissipation method. Penman-Monteith based evapotranspiration models of increasing complexity were tested against the tree water use measurements to assess the role of environmental and tree related factors in tree transpiration. Alnus and Tilia respectively used 1.1 and 0.8 l of water per m² of leaf area per day under ample water conditions, but the annual variation was high. The Penman-Monteith evapotranspiration estimate and soil water status changes explained over 80 % of the variation in tree transpiration when the model was parameterized annually. The addition of tree crown surface area in the model improved its accuracy and diminished variation between years and sites. Using single parameterization over all four years instead of annually varying one did not produce reliable estimates of tree transpiration. Tree transpiration, scaled to different canopy cover percentages, implied that the columnar Alnus trees could transpire as much as all annual rainfall at or less than 50 % canopy cover.     

Water sources of urban trees in the Los Angeles metropolitan area

In semi-arid cities, urban trees are often irrigated, but may also utilize natural water sources such as groundwater. Consequently, the sources of water for urban tree transpiration may be uncertain, complicating efforts to efficiently manage water resources. We used a novel approach based on stable isotopes to determine tree water sources in the Los Angeles basin, where we hypothesized that trees would rely on irrigation water in the soil rather than develop deep roots to tap into groundwater. We evaluated the oxygen (δ¹⁸O) and hydrogen (δD) isotope ratios of xylem water, irrigation water, soil water, and groundwater in a study of temporal patterns in water sources at two urban sites, and a study of spatial patterns at nine urban sites and one “natural” riparian forest. Contrary to our hypothesis, we found that despite frequent irrigation, some trees tap into groundwater, although in most species this was a small water source. Some trees appeared to be using very shallow soil water at <30 cm depth, suggesting that these mature urban trees were quite shallowly rooted. In the natural site, trees appeared to be using urban runoff in addition to shallow soil water. We were able to identify tree uptake of precipitation at only 3 sites. The results show that some irrigated trees utilize groundwater and do not rely solely on irrigation water, which may make them able to withstand drought and/or water conservation measures. However, some irrigated trees may develop very shallow root systems, which may make them more susceptible.     

Comparison of water-use characteristics of landscape tree (<Emphasis Type="Italic">Tabebuia argentea</Emphasis>) and palm (<Emphasis Type="Italic">Ptychosperma macarthurii</Emphasis>) species in a tropical roof garden with implications for urban water management

In cities, landscape palms and trees are planted for scenic views and normally maintained with frequent irrigation. With similar water input, their morphological difference may lead to different water-use that varies seasonally. Thus, evaluating their water-use patterns is necessary to achieve proper urban water management. Here, we examined water-use characteristics of Tabebuia argentea and Ptychosperma macarthurii, a tree and a palm species, in a roof garden in Bangkok, Thailand. Self-constructed Granier’s probes were used for sap flux measurement and monitored for five months in 2016. Results showed that palm transpired 3–4 times higher water than tree daily. With frequent watering, tree was more sensitive to increasing vapor pressure deficit (D) than palm on rain-free days. When rainfall occurred, however, both species became less sensitive to D and continued consuming more water at high D. Extending the analysis to include a hypothetical warming climate with +4.8 °C temperature, we found that tree saved more water than palm on rain-free days. However, daily transpiration of both species increased similarly by 14–18% on rainy days. These results imply that Tabebuia argentea may provide ecosystem benefits by conservatively using water under drought and decelerating runoff from the garden when storms come. In contrast, Ptychosperma macarthurii may provide ecosystem disservice with high water-use in dry season but may slow down runoff in wet season and therefore benefiting downstream ecosystems. These findings are useful for selective planting associated with future changes in precipitation patterns, leading to sustainable urban water management.     

Structural elements as barriers against wear in urban woodlands

The effect of structural elements of woodlands (trees, rocks, topography, etc.) on the spatial distribution of wear was studied in 30 sites in the cities of Helsinki and Vantaa, Finland. Discriminant analysis showed that the size of the adjacent human population and structural elements within study sites were important in distinguishing sample plots with a lot of path area (6 m²/30 m²) from those with little or no path area (>6 m²/30 m²). The higher the structural elements, the more effectively they functioned as barriers against wear. Thickets of small trees (dbh > 10 cm), topographical elements, and fallen trees seemed most effective, and big trees (dbh 10 cm) least effective as barriers. It was concluded that natural barriers could be used to limit wear in urban woodlands.     

Factors related to tree growth across urban-rural gradients in the Midwest,USA

Several environmental factors influence tree growth at any site. The objective of this study was to examine the relationship between biotic and abiotic factors and tree growth rate (mean ring width averaged over the last 10 years) in settings ranging from urban to rural. Six clusters, each with five communities and two rural parks, were sampled in Illinois, Iowa, Minnesota, Missouri, and Wisconsin, for a total sample of 320 trees. Within each community, trees in parks, and along residential and commercial streets were sampled. Five species were sampled: silver maple (Acer saccharinum L.), honeylocust, (Gleditisia triacanthos L.), hackberry (Celtis occidentalis L.), black maple (Acer nigrum Michx F.), and basswood (Tilia americana L.). Factors were investigated for three scenarios: (i) all trees sampled in all clusters, (ii) a single species, all clusters, and (iii) all species, a single cluster.Baseline variables (cluster, place population, site, species, and age) accounted for 49–71% of observed variation in growth rate. Combined biotic factors accounted for 5 to 6% of observed variation. For all species in a single cluster, combined abiotic factors accounted for 11% of observed variation. Biotic factors related to growth rate detected using multivariate analyses included number of other trees within 9 m, presence of disease and insects, and human-induced mechanical injury. Abiotic factors that were related to tree growth included presence of pavement and core bulk density. For trees in rural parks, number of other trees within 20 m, and for trees in both rural and community parks, number of other trees within 9 m of sample trees were associated with decreased growth rate.     

A review of tree root conflicts with sidewalks,curbs, and roads

Literature relevant to tree root and urban infrastructure conflicts is reviewed. Although tree roots can conflict with many infrastructure elements, sidewalk and curb conflicts are the focus of this review. Construction protocols, urban soils, root growth, and causal factors (soil conditions, limited planting space, tree size, variation in root architecture, management practices, and construction materials) are discussed. Because costs related to sidewalk and curb damage are substantial, a review of research addressing repair, mitigation, prevention, and litigation costs is included. Finally, future research needs are discussed.

Potential for conflicts between trees and sidewalks/curbs is high when one or more of these factors are present: tree species that are large at maturity, fast growing trees, trees planted in restricted soil volumes, shallow top soil (hard-pan underneath top-soil), shallow foundations underneath the sidewalk (limited or no base materials), shallow irrigation, distances between the tree and sidewalk of less than 2.0–3.0 m., trees greater than 15 to 20 years old.

The results of this survey indicate that cities are spending substantial sums of money to address conflicts between street tree roots and infrastructure. It can be inferred that most of these expenditures are spent dealing with problems that already exist. However, this raises the question: How much is being spent now to ensure that conflicts are minimized in the future?

Future research should concentrate on plant factors, site design, and construction of sidewalks and curbs. Also, more knowledge is needed about interactions between root growth and management techniques, such as pruning and irrigation. Finally, there is need for studies that will assist policy-makers to efficiently allocate funds among repair, mitigation, prevention, and legal remedies.

     

Photosynthetic CO<Subscript>2</Subscript> uptake and carbon sequestration potential of deciduous and evergreen tree species in an urban environment

Urban tree planting programmes are increasingly promoted as a way to reduce atmospheric carbon dioxide (CO₂) mixing ratios. However, few studies have investigated the photosynthetic CO₂ uptake potential of different urban tree species across seasons. In particular little is known about photosynthetic CO₂ uptake in cities with a subtropical, oceanic climate where evergreen species are dominant. We addressed this shortcoming by measuring net photosynthetic rates of ten native and exotic tree species during different seasons and times of the day in Auckland, New Zealand. We also assessed the potential of leaf nitrogen (N) concentration as a proxy for net photosynthetic capacities of urban trees, which is of particular importance to upscale leaf-level photosynthetic CO₂ uptake to local and regional scales. In addition, we compared measured net photosynthetic capacities (light-saturated net photosynthetic rates) with carbon (C) sequestration rates estimated using tree growth measurements and allometric equations. Mean net photosynthetic capacities ranged between 2.37 and 10.48 μmol m^?2 s^?1 across all seasons and were closely related to tree C sequestration rates, suggesting that increased photosynthesis enhances growth rates and therefore tree C sequestration rates. Given that winter net photosynthetic capacities remained high in evergreen species (3.38–13.96 μmol m^?2 s^?1), with almost 50% higher mean net photosynthetic capacity compared to summer across all species, we suggest that tree planting programmes for CO₂ mitigation should favour long living evergreen tree species with high basal area increments (BAI). Leaf N explained 43% and 57% of the variability of photosynthetic capacities across species in summer and winter, respectively. These results indicate that leaf N may be used as a proxy for net photosynthetic capacities of commonly planted urban trees in Auckland. However, further research is required to provide robust models that may be used to estimate photosynthetic CO₂ uptake at a local and urban scale.     

Effects of ground surface permeability on the growth of urban linden trees

Street trees are an important part of urban vegetation due to their provisioning of different types of ecosystem services such as local climate regulation and contribution to aesthetical and recreational values. In order to provide these services, urban trees need to endure many stress factors not present in natural environments, such as the widespread use of impervious surfaces in the vicinity of street trees. However, few studies have evaluated the effect of this potential stress factor on urban tree growth. The aim of this study was therefore to investigate how ground surface permeability affects stem and current-year shoot growth of linden (Tilia europaea) street trees in Gothenburg, Sweden. We found that a small fraction of permeable ground surface in the vertically projected tree crown area caused lower stem growth and strongly suppressed current-year shoot growth. This finding can guide future city planning, demonstrating that the vitality of street trees is compromised when the permeable surface area in the vicinity of the tree is small.     

Street trees and rural conspecifics: Will long-lived trees reach full size in urban conditions?

Urban conditions are known to affect tree growth, but not all trees respond similarly to presumed stress. I test a hypothesis that successional status of hardwood tree species, rather than taxon, will differentially affect tree size relative to age, in forest versus street plantings. In central Ohio, USA, samples (N = 230) representing 15 native tree species were matched for size between rural woodlot and city street-side conditions. Their girth was measured and their age determined by a count of annual growth rings. Age and size data were analyzed by a general linear model. Most urban trees had smaller trunk diameters than rural conspecifics of the same age. However, trees of early and mid-successional ecologies, despite smaller girth, showed no reduction in growth rate over time. Late successional species appeared to be affected by proximity to impervious areas, showing reduced growth rates, and by inference,reduced ultimate size.     

Risk of bird predation and defoliating insect abundance are greater in urban forest fragments than street trees

Predation by natural enemies is important for regulating herbivore abundance and herbivory. Theory predicts that complex habitats support more natural enemies, which exert top-down control over arthropods and therefore can reduce herbivory. However, it is unclear if theory developed in other more natural systems similarly apply to predation by vertebrate and invertebrate natural enemies across urban habitats of varying complexity. We used plasticine caterpillar models to assess risk of predation by birds and insects, collected leaf-feeding arthropods, and measured herbivory in willow oak trees (Quercus phellos) in two seasons to determine how predation influenced herbivory across urban forest fragments, street trees planted near forest fragments, and downtown street trees. Predation attempts by birds and abundance of chewing folivores were greater on trees growing in urban forest fragments than downtown street trees. Bird predation attempts and herbivory levels were inconsistent for near-forest trees. Predation attempts by arthropods did not statistically vary among the three urban tree habitats. Contrary to expectations based on theory, chewing folivore abundance and herbivory were generally highest on trees growing in urban forests, the most complex habitat we studied, and the habitat where risk of bird predation was greatest. We suggest that urban forest fragments provide better habitat than other urban landscapes for both urban birds and chewing folivores by having greater habitat complexity. Therefore, basal resources, such as availability of suitable habitat, mediate top-down effects on herbivores in cities.

     

The why and how of volunteering

Volunteers: A Social Profile, by Marc A. Musick and John Wilson. Bloomington: Indiana University Press, 2007. 680 pp., $39.95 cloth. The Decision to Volunteer: Why People Give Their Time and How You Can Engage Them, by Beth Gazley and Monica Dignam. Washington, D.C.: ASAE and the Center for Association Leadership, 2008. 144 pp., $89.85 paper. Challenges in Volunteer Management, edited by Matthew Liao‐Troth. Charlotte, N.C.: Information Age, 2008. 292 pp., $73.99 cloth, $39.99 paper.     

A GIS for environmental assessment of air pollution impacts on urban clusters and natural landscape at Rosetta City and region,Egypt

An air pollution problem is taking place in the Rosetta region resulting from the brick industry. Polluting point sources cause plumes that disperse by the prevailing wind, covering urban areas of Rosetta City and surrounding landscape of agricultural fields. A model for pollutants plumes was designed through a GIS to calculate the dispersal of total suspended particulate (TSP) loads over the landscape and to estimate its spatial distribution and to analyze its relationship with other geographic land use attributes.TSP pollutant concentrations starting from 100 g/m³ cover more than 34 km² of sensitive land cover through all the year. A concentration level of 100 g/m³ affects about 93% of the sensitive palm trees cultivation, 47% of cultivated land, and 92% of urban areas. TSP concentration level of 200 g/m³ was found to be affecting the same percentage of built-up urban areas.Concentration levels exceed the permissible limits mentioned in the Egyptian law of environment (90 g/m³). The situation is hygienically deteriorated, and large areas of agricultural land are strongly affected or subjected to future impact. Recommended measures are mostly involved with transferring this industrial activity to a safer location at the southwest of the city. The study proposes that brick mills sites on the river Nile bank be utilized for urban development projects and for the promotion of tourism.