Influence of evaporative cooling by urban forests on cooling demand in cities

Trees provide important ecosystem services to urban human society. Their absence can lead to more pronounced environmental and social consequences, for example the urban heat island effect. Evapotranspiration (Et) from trees reduces air temperature in the urban microclimate by converting sensible heat to latent heat. Quantification and valuation of the ecosystem services provided by urban trees is important for improving cost-benefit evaluations in support of protecting tree planting and maintenance budgets and, thus, for building climate change resilience into cities. Inclusion of Et cooling could improve ecosystem service valuation models by producing a more complete picture of the benefits that urban trees provide to society. This study explores two approaches for evaluating climate regulation as an ecosystem service of urban trees. Firstly, an enthalpy-based approach was adopted to valuate latent heat of evaporation from tree transpiration (in three case study urban forests) by equating it to an equivalent service from an active direct evaporative cooling system. Secondly, energy savings to air-conditioned buildings was modelled using TRNSYS and TRNFLOW simulation programs with and without air precooled and humidified by urban trees. Trees are shown to provide substantial urban cooling with an annual valuation of £84 m estimated using the enthalpy-based approach, or ranging from £2.1 m to £22 m using TRNSYS and TRNFLOW dynamic simulation programs; both for inner London case study. The latter savings arose from a modelled 1.28 – 13.4% reduction in air-conditioning unit energy consumption. Challenges around assumptions of homogeneity in both built form and urban forest canopy effects are discussed. The case study examples highlighted differences in Et cooling between tree species, with Castanea sativa, Prunus avium, Quercus petraea, Platanus hybrida and Fagus sylvatica typically providing more Et cooling than any of the other tree species commonly found in urban forests. The research highlighted a shortage of published Et data, particularly for urban environments

Interactive effects of composted green waste and earthworm activity on tree growth and reclaimed soil quality: a mesocosm experiment

On reclaimed landfill sites, the addition of organic matter such as composted green waste (CGW) to soil-forming materials can support tree survival and growth. CGW addition may also assist the establishment of sustainable earthworm populations, and in turn these organisms can promote further soil development through their burrowing and feeding activity. Despite such potentially mutual benefits, little research has been carried out into CGW and earthworm interactions with trees on reclaimed land. A twelve month, open field nursery experiment revealed the responses of the interactions between two tree species; Alnus cordata (Betulaceae) and Acer platanoides (Sapindaceae), CGW and the earthworms Aporrectodea longa (Lumbricidae) and Allolobophora chlorotica (Lumbricidae) in reclaimed soil. Controlled mesocosm conditions permitted a detailed investigation into the factors affecting tree growth and nutrient uptake, soil nutrient cycling and earthworm population dynamics. Results revealed that A. cordata growth was unaffected by CGW or earthworm addition. There was, however, a significant positive synergistic effect of earthworm activity and CGW addition on A. platanoides growth. CGW addition significantly increased levels of organic carbon and essential plant macro-nutrients in reclaimed soil while earthworm activity assisted decomposition of both leaf litter and CGW. Findings showed that CGW may serve as a suitable early source of organic matter to support earthworm population establishment on reclaimed sites. This experiment demonstrates that CGW improves reclaimed soil quality, thereafter supporting tree establishment and growth on reclaimed landfill

The role of engineered tree pit solutions in nature-positive civil engineering

Successfully establishing and growing street trees presents significant challenges and traditional techniques are associated with elevated tree mortality. Moreover, securing appropriate soil volumes for trees is a substantial challenge, particularly in modern street engineering where the grey infrastructure is prioritised over tree success. Engineered tree pit solutions can counteract this situation. They enable trees and grey infrastructure to coexist, providing improved rooting environments, load-bearing structural support conforming to engineering specifications, and the ability to manage stormwater runoff within one tree pit design. This article presents a literature-informed overview of the current technologies applicable to new-build and retrofit scenarios that integrate street trees and pavements, enabling nature-positive, resilient tree pit designs conducive to tree growth. We focus on the solutions most commonly employed in practice - structural growing media and crate systems - outlining their constituents, construction and considerations for success. This article informs built environment practitioners, policymakers and researchers on innovations translatable into practical techniques to enhance tree pit design and optimise street trees as multifunctional nature-based solutions

Challenges for tree officers to enhance the provision of regulating ecosystem services from urban forests

Urbanisation and a changing climate are leading to more frequent and severe flood, heat and air pollution episodes in Britain's cities. Interest in nature-based solutions to these urban problems is growing, with urban forests potentially able to provide a range of regulating ecosystem services such as stormwater attenuation, heat amelioration and air purification. The extent to which these benefits are realized is largely dependent on urban forest management objectives, the availability of funding, and the understanding of ecosystem service concepts within local governments, the primary delivery agents of urban forests.This study aims to establish the extent to which British local authorities actively manage their urban forests for regulating ecosystem services, and identify which resources local authorities most need in order to enhance provision of ecosystem services by Britain's urban forests.Interviews were carried out with staff responsible for tree management decisions in fifteen major local authorities from across Britain, selected on the basis of their urban nature and high population density. Local authorities have a reactive approach to urban forest management, driven by human health and safety concerns and complaints about tree disservices. There is relatively little focus on ensuring provision of regulating ecosystem services, despite awareness by tree officers of the key role that urban forests can play in alleviating chronic air pollution, flood risk and urban heat anomalies. However, this is expected to become a greater focus in future provided that existing constraints ? lack of understanding of ecosystem services amongst key stakeholders, limited political support, funding constraints ? can be overcome.Our findings suggest that the adoption of a proactive urban forest strategy, underpinned by quantified and valued urban forest-based ecosystem services provision data, and innovative private sector funding mechanisms, can facilitate a change to a proactive, ecosystem services approach to urban forest management

Achieving impact from ecosystem assessment and valuation of urban greenspace: The case of i-Tree Eco in Great Britain

Numerous tools have been developed to assist environmental decision-making, but there has been little examination of whether these tools achieve this aim, particularly for urban environments. This study aimed to evaluate the use of the i-Tree Eco tool in Great Britain, an assessment tool developed to support urban forest management. The study employed a documentary review, an online survey, and interviews in six case study areas to examine five impacts (instrumental, conceptual, capacity-building, enduring connectivity, and culture/attitudes towards knowledge exchange) and to identify which factors inhibited or supported achievement of impact. It revealed that the i-Tree Eco projects had helped to increase knowledge of urban forests and awareness of the benefits they provide. While there was often broad use of i-Tree Eco findings in various internal reports, external forums, and discussions of wider policies and plans, direct changes relating to improved urban forest management, increased funding or new tree policies were less frequent. The barriers we identified which limited impact included a lack of project champions, policy drivers and resources, problems with knowledge transfer and exchange, organisational and staff change, and negative views of trees. Overall, i-Tree Eco, similar to other environmental decision-making tools, can help to improve the management of urban trees when planned as one step in a longer process of engagement with stakeholders and development of new management plans and policies. In this first published impact evaluation of multiple i-Tree Eco projects, we identified eight lessons to enhance the impact of future i-Tree Eco projects, transferable to other environmental decision-making tools

Using a Conceptual Site Model for Assessing the Sustainability of Brownfield Regeneration for a Soft Reuse:A Case Study of Port Sunlight River Park (U.K.)

Brownfield regeneration to soft reuse such as recreation and amenity has become increasingly common due to the demand for the potential environmental, social and economic benefits that it can deliver. This has led in turn to an increased demand for improved tools to support decision-making for this style of regeneration: tools which are simple to use, based on robust scientific principles and preferably which can ultimately link to quantitative or semi-quantitative cost-benefit analyses. This work presents an approach to assessing and comparing different scenarios for brownfield regeneration to soft reuse and other end-points. A “sustainability linkages” approach, based on sustainability assessment criteria produced by the UK Sustainable Remediation Forum (SuRF-UK), is developed and used in a refined qualitative sustainability assessment, and applied to develop a conceptual site model of sustainability, for a specific case study site (Port Sunlight River Park, U.K., a public leisure park established and maintained on a capped and managed former landfill site). Ranking, on an ex post basis, highlighted the clear sustainability advantages that the establishment of the Port Sunlight River Park has compared with a hypothetical non-development scenario. The conceptual site model provides a clearer basis for understanding cause and effect for benefits and disbenefits and a rationale for grouping individual effects based on their ease of valuation, providing a road map for cost-benefit assessments by (1) being able to match specific linkages to the most appropriate means of valuation, and (2) transparently connecting the sustainability assessment and cost benefit assessment processes.</p

Effects of composted green waste on soil quality and tree growth on a reclaimed landfill site

The addition of composted green waste (CGW) into soil-forming materials during land reclamation can benefit tree growth by improvement of soil properties and provide an effective waste management solution. CGW addition may also assist the establishment of earthworm populations, which in turn aid soil development through their burrowing and feeding activities. An experiment was set up on a reclaimed landfill site, to measure the effects of CGW addition on soil physical and chemical quality and subsequently on the survival and growth of two tree species (Acer platanoides and Alnus cordata). A further objective was to measure the influence of earthworm (Aporrectodea longa) addition on the above. CGW addition led to significantly greater A. cordata growth (height and diameter) and increased survival rate. No benefits from CGW addition were observed on A. platanoides growth or survival, although this is likely due to soil drought conditions during establishment. CGW addition significantly increased levels of organic carbon and essential plant macro-nutrients in the reclaimed soil. Soil pH rose slightly across all treatments, with highest final pH under the control treatment. Earthworm inoculation, as used, was unsuccessful at increasing population density of A. longa. This experiment showed that CGW application can effectively improve tree establishment and soil quality on reclaimed landfill; however tree species selection is an important consideration, based on individual species tolerance and sensitivity to certain soil conditions. These findings will be informative to decisions on soil amendment and afforestation activities on similar reclaimed landfill sites

Valuing Wrexham's Urban Forest

Urban forests are a valuable source of ecosystem services in towns and cities. They help us alleviate problems associated with densely packed populations by improving local air quality, capturing carbon and reducing flooding. They also provide food and habitat for animals, such as birds and bees, and improve social cohesion in communities.However, the value of urban trees, both quantifiable and otherwise, is often overlooked within planning developments. By valuing the quantifiable services provided by trees in Wrexham County Borough, Wrexham County Borough Council and Natural Resources Wales can increase the profile of the County‟s urban forests, ensuring their value is maintained and improved upon. In addition, valuing these ecosystem services helps town planners, landscape architects and tree officers to plan where trees will be planted for the maximum benefit.A survey of Wrexham County Boroughs trees‟ to value a number of ecosystem services was undertaken in summer 2013 with the aid of i-Tree Eco, used for the first time in Wales. i-Tree Eco is a model developed by the US Forest Service that allows scientists to measure a range of ecosystem services provided by urban trees, from carbon sequestration to pollutant removal. The study was funded by Natural Resources Wales and Wrexham County Borough Council and was carried out by Forest Research. The quality of life for residents of Wrexham is significantly improved by its urban forest, helping alleviate flash flooding and sewer blockages, providing cleaner air and supporting wildlife such as pollinators. In addition, Wrexham‟s urban forest contributes significantly to the local economy, saving around £1.44 million in services per year. This would be enough money to plant nearly 800 medium sized oak trees in Wrexham and iscomparable to the amount needed to refurbish Wrexham cemetery (Wrexham.com, 2014). Wrexham has a high density of trees but low canopy cover compared to similar sized towns. A further 28% of Wrexham‟s urban space could be planted with trees, bringingWrexham in line with other urban areas. Wrexham‟s urban forest could also be improved by planting a higher diversity of tree species, improving its resilience to pests and diseases. The number of large trees in Wrexham is above average for the UK and, in particular,there are many impressive old oaks. However, there are fewer large trees than recommended for a future-proofed urban forest, suggesting some room for improvement. Increasing planting of large stature trees may future proof Wrexham‟s impressive stock of large growing trees. A summary of key results is presented on page 5