Community perceptions of ecosystem services and disservices linked to urban tree plantings

The planting of trees in streets and parks is critical for urban greening efforts that seek to improve climate-change resilience in cities around the world. Ecosystem services provided by urban trees range from mitigating urban heat island effects to enhancing human well-being and conserving native biodiversity. At the same time, such tree services trade off with disservices that include risk to human safety from falling branches and infrastructure damage from root growth. Here, we performed a survey of residents of a sub-tropical region in eastern Australia to determine community perceptions of the ecosystem services and disservices linked to urban tree plantings. Our aim was to better understand the diverse perceptions of the community, prior to on-the-ground implementation of urban greening, to help guide planting programs in streets and parklands that are vulnerable to UHI effects in the region. We found strong evidence for a high level of public awareness about the beneficial ecosystem services that urban trees can provide. A broad spectrum of beneficial tree services were valued highly by the community in their urban environment including the planting of native trees that can attract and provide food for preferred wildlife; provide shade and reduce heat; allow for a strong connection with nature; have the potential to store carbon to mitigate climate change; provide a level of protection from bushfires; have aesthetically pleasing properties; and produce food for people. At the same time, however, community concerns about tree disservices were concentrated primarily on root damage to infrastructure as well as property damage and injury from falling branches. Our elicitation of community attitudes to tree services and disservices will allow for residents’ most important values and strongest concerns about trees to be explicitly taken into account when establishing a community-inclusive approach to urban tree planting.     

Energy balance of six common landscape surfaces and the influence of surface properties on gas exchange of four containerized tree species

Gas exchange and growth of woody landscape plants is strongly affected by underlying surfaces. In urban areas, plants are subjected to energy balance characteristics of a variety of surfaces. We investigated energy balance properties of six urban surfaces: asphalt, gravel rock mulch, lava rock mulch, concrete, pine bark mulch, and turf. Each summer over a 3-year period, incoming global shortwave radiation, surface temperature, surface reflectivity (albedo), soil temperature below each surface, and soil heat flux were measured for each surface, and total incoming radiation, thermal conductivity, and longwave radiation emitted by each surface were calculated. Differences in surface properties were analyzed by regression analysis. Albedo was greatest for concrete and least for lava rock mulch, while thermal conductivity was greatest for asphalt and least for lava rock and pine bark mulches. Under maximum incoming total radiation, regression analysis indicated: soil heat flux was greatest under asphalt and concrete and least under lava rock and pine bark mulches; soil temperature below each surface was greatest for asphalt and concrete and least for pine bark mulch; surface temperature was greatest for pine bark mulch and least for turf; and longwave radiation flux of each surface was greatest for pine bark mulch and least for turf. This research revealed that more energy was conducted into the soil below asphalt and concrete, and that a greater portion of incoming radiation was prevented from entering the soil below pine bark and lava rock mulches than below other surfaces. Due to these effects, and the lack of evaporative cooling, surface temperatures were greater, and more longwave radiation was emitted from non-vegetative surfaces than from turf. In a concurrent study, we investigated if the energy balance of turf, pine bark mulch, and asphalt surfaces influenced gas exchange of four containerized tree species grown over each surface. On several occasions over a 2-year period, morning-to-evening measurements of stomatal conductance, leaf temperature, and plant water loss were made on containerized Bechtel crabapple (Malus ionensis ‘Plena’), Norway maple (Acer platanoides ‘Crimson King’), globe willow (Salix matsudana ‘Navajo’) and American plane tree (Platanus occidentalis). Leaves over pine bark mulch and asphalt intercepted more longwave radiation and generally had greater leaf temperature and leaf-to-air vapor difference than leaves over turf. As a result, trees over non-vegetative surfaces generally had lower stomatal conductance and water loss than trees over turf.     

Effect of the elevated ozone on greening tree species of urban: Alterations in C-N-P stoichiometry and nutrient stock allocation to leaves and fine roots

Anthropogenic ground-level ozone (O₃) pollution can alter the phosphorus (P), carbon (C), and nitrogen (N) of terrestrial plants’ ecological stoichiometry, which in turn affects forest productivity, nutrient utilization, and carbon sink capacity. However, there is still quite a lot of uncertainty regarding the impact of high O₃ levels on C-N-P stoichiometry in organs with a rapid turnover (i.e., fine roots and leaves) across varied functional types. This study investigated the effects of O₃ on the stoichiometry of C-N-P nutrient allocation of stocks to various plant organs, with a special focus on tree species frequently employed for urban greening. The impact of O₃ on C-N-P stoichiometry among different functional tree types was subsequently evaluated by reviewing the published literature. Under a pooling of all species, elevated O₃ decreased and leaf C and P concentrations increased, thereby decreasing the leaf C: P ratio. Elevated O₃ increased the N concentration in fine roots, thereby decreasing the C: N ratio, although no significant impact was observed in leaves. Elevated O₃ significantly reduced the leaf stocks of C (CS_leaf) and N (NS_leaf), however, there was no observed variation in these stocks in fine roots. The content of P, C, and N in fine roots and leaves in evergreen broadleaf species exceeded those in deciduous species. Elevated O₃ significantly reduced CS_leaf, NS_leaf, and PS_leaf in deciduous broadleaf species, whereas there was a significant reduction for the same in evergreen species. The literature analysis further demonstrated a larger O₃-induced increment in leaf P concentration in deciduous species as compared to evergreen species. Elevated O₃ significantly increased the difference in C and N stocks between fine roots and leaves in deciduous broadleaf species, whereas this difference was observed to decrease in evergreen species. The results of this study can facilitate an improved understanding of ecological stoichiometric responses of urban greening tree species under O₃ stress and the resulting nutrient use strategies.     

Survival is not enough: The effects of microclimate on the growth and health of three common urban tree species in San Francisco,California

Urban forest managers must balance social, economic, and ecological goals through tree species selection and planting location. Ornamental trees are often popular in tree planting programs for their aesthetic benefits, but studies find that they have lower survivability and growth compared to larger shade trees. To maximize ecosystem services within these aesthetic preferences, it is important to select species carefully based on their ability to grow in each particular climate. However, little locality-specific and species-specific data exist on urban trees in many regions. This study examines the growth, survival, and vigor of three common ornamental street trees in San Francisco’s three different microclimate zones after over 16 years since planting. While we found over 70% survival for all three species throughout the city, there were significant differences in health and vigor among microclimates for each species, likely due to differences in drought-tolerance. While Arbutus had the greatest proportion of healthy trees in the Fog Belt and Sun Belt zones, Prunus cerasifera had the greatest proportion in the Sun Belt, and Prunus serrulata had the greatest proportions in the Transition and the Sun Belt zones. This species-specific and climate-specific information will better equip urban foresters to target both planting and tree-care of these popular species appropriately to maximize the benefits provided by these street trees while still maintaining a diverse canopy. Finally, we argue that simple survival calculations can mask more complex differences in the health and ability of different urban tree species to provide ecosystem services.     

Selecting trees for urban paved sites in Scandinavia – A review of information on stress tolerance and its relation to the requirements of tree planners

Urban paved sites are complex stress environments and when selecting trees for such sites, tree planners must prioritise stress tolerance above aesthetic appeal and functional aspects. This requires detailed information about the tolerance of tree species to environmental stresses, so as to support urban tree planners in selecting a wide range of trees. In Scandinavia there is currently no overview of the extent to which the character of information about stress tolerance and its dissemination in books and papers support urban tree planners in selecting a wide range of species for paved sites. Books on dendrology, literature on plant use in cities, tree nursery catalogues and scientific papers were therefore reviewed. For the review, eight tree species were selected along a gradient representing their intensity of use in Northern Europe. We examined the character of information and assessed it relative to tree planners’ requirements for information to be; contextual, local to Scandinavia, referring to existing plantings in paved sites and recommendations for use of the species in paved sites. The results showed that existing information is piecemeal and that most is either too general (dendrology literature) or too specific or contradictory (scientific literature) to meet the requirements of urban tree planners, while books intended for plant use in cities do not sufficiently integrate the local perspective. Moreover, contextual information local to the Scandinavian region is mainly provided for already much used species. These findings led to suggestions on how future urban forestry and arboriculture research and dissemination efforts in Scandinavia can encourage tree planners to use a greater variety of tree species in urban paved sites.     

Effect of different rates of composted organic amendment on urban soil properties,growth and nutrient status of three Mediterranean native hedge species

Increasing green space, especially in densely built-up areas is considered to be a valuable climate change adaptation response in order to reduce the threat of high temperatures to human health and comfort and to controlled global greenhouse gas emissions. Practical responses to climate change, under urban conditions, in order to avoid or reduce trees and shrubs vulnerability, can be considered drought resistant planting approaches, as the addition of organic amendeds to soil. The improvement of physical–chemical soil quality is a key step for carrying out xeriscaping programs of urban green spaces in Mediterranean semiarid areas. Organic amendments, particularly compost, have been receiving a renewed attention not only in horticulture but also in the context of restoring disturbed urban soils to address environmental issues as well as to improve trees and shrubs growth. The influence of increasing rates (0, 15, 30, and 45%) of composted sewage sludge (SSC) placed in the plantation hole on both urban soil properties and growth for three native Mediterranean woody hedge species was monitored over a 2-year period after planting. The experiment was supported by a xerogardening project in an urban context under semi-arid conditions. The results indicate that the urban soil physical characteristics were positively influenced by the addition of SSC: the 45% rate showed an increase in both moisture and infiltration values, thereby increasing the volume of plant-available water in the soil. The chemical properties of the amended soils were also directly affected by the SSC rate, but the effect of the compost on organic matter, nitrogen and potassium contents decreased over time. Our results prove that the hedge growth response to the compost treatments is also highly dependent on the rate of compost used. At the end of the trial, in Rhamnus and Myrthus plants 30% compost level guarantees the best performance; in fact, the further addition of 15% of compost led to a significant decrease in hedge and diameter values, in particular in Myrtle. This could be explained by the high pH at 45% compost, which would seem not to suit the physiology of the two species. On the other hand, in Phillyrea plants, the rate of 45% compost gives high performance equal to that of 30%; it would therefore seem that the high pH at 45% compost does not influence the nutritive elements’ absorption and, as a consequence, the growth. The use of composted sludge as an amendment for sclerophyllous could be feasible and, what is more, helpful to mitigate the environmental impact of organic waste disposal. Moreover more natural vegetation can be introduced into urban parks and green spaces in semi-arid environments to encourage sustainable landscaping and xerogardening.