ARBORICULTURE ARBORICULTU & CONTENTS Community Forestry. David Armson, Mohammad Asrafur Rahman, and Anthony Roland Ennos A Comparison of the Shading Effectiveness of Five Different Street Tree Species in Manchester, UK .....................................................................................................................157 Abstract. One major benefit of urban trees is the shade they provide on sunny days; this reduces the heat stored in engineered surfaces and lowers the heat load on people, increasing their comfort. This study compared the shading effectiveness of five small street tree species within the urban landscape of Manchester, UK. The area of shade produced by each tree during early and midsummer 2012 was calculated from morphological measurements, such as canopy height, width, and aspect ratio. The effect of tree shade on air, mean radiant and surface temperatures was also compared and related to the leaf area index (LAI) of the canopy. It was found that tree shade reduced mean radiant temperatures by an average of 4°C, though neither tree species nor LAI had a significant effect. Tree shade reduced surface temperatures by an average of 12°C, and the tree species and LAI both had sig- nificant effects. Tree species with higher LAI, Crataegus laevigata and Pyrus calleryana, provided significantly more cooling than the other species, and surface temperature reduction was positively correlated with LAI. This study has shown that trees are useful in improving both human thermal comfort and reducing surface temperatures in urban areas, and that selection of tree species with high LAI can maximize the benefits they provide. Key Words. England; Human Thermal Comfort; Manchester; Mean Radiant Temperature; Surface Temperature; Tree Shade; United Kingdom; Urban Heat. Mark G. Stewart, Dealga O’Callaghan, and Mark Hartley Review of QTRA and Risk-based Cost-benefit Assessment of Tree Management ........................165 Abstract. Quantified Risk Assessment (QRA) has been in wide use in risk management since the 1960s for systems ranging from aviation, nuclear power, and offshore platforms to medical treatment and pharmaceuticals. The Quantified Tree Risk Assess- ment (QTRA) system is examined considering the principles of QRA. A case study of 14 fig trees in Newcastle, Australia, illustrates some limitations of the QTRA process, and extrapolating risks for a single tree to a group of trees. There is a need for any risk manage- ment process involving trees, not only to assess the risk, but to weigh the benefits provided by trees by a risk-based cost-benefit analysis. Tree risk assessors should rely on benchmarks to ensure that their assessment is not outside of the realms of reality or scientific rigor. Key Words. Australia; Cost-benefit Analysis; Quantified Tree Risk Assessment; Risk; Risk Management; Trees. URBAN FORESTRY Volume 39, Issue 4, July 2013 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) ® www.isa-arbor.com Stephen C. Grado, Marcus K. Measells, and Donald L. Grebner Revisiting the Status, Needs, and Knowledge Levels of Mississippi’s Governmental Entities Relative to Urban Forestry ..........................................................................................................149 Abstract. In 2004, Mississippi State University researchers determined the status, needs, and knowledge levels of Mississippi’s community leaders and communities relative to urban and community forestry benefits, programs, funding opportunities, and program implementation. As a result, this project’s goals were to build on past research and identify trends for past and current involvement and future interest levels among Missis- sippi’s small (<2,000 people) to large (>10,000 people) communities for urban and community forestry programs and assistance. This current effort revisited these communities, previously surveyed in 2004, and highlighted changes in knowledge levels and various activities and programs undertaken. A mail survey was sent to 293 Mississippi communities with 163 surveys returned for a response rate of 55.6%. In general, communi- ties responding indicated that a sizable number of officials have increased their awareness or interest in urban and community forestry. Communi- ties that wanted to establish programs the most again cited a lack of funding as the reason for not initiating projects or sustaining existing programs. Greater effort in disseminating information on funding opportunities was seen as necessary, given that most Mississippi communities were only aware of a few national programs. Participation in statewide or local urban forestry programs and activities was minimal. The authors’ previ- ous study found that without quality, updated information on urban and community forestry and reliable funding, communities are limited in undertaking systematic planning and associated programs utilizing arboreal resources. Good information distribution, which has improved, and reliable funding are still limiting communities in undertaking systematic planning and associated urban and community forestry programs. Key Words. Large Communities; Medium-sized Communities; Mississippi; Reassessment; Small Communities; Survey Research; Urban and ® ©2013 | International Society of Arboriculture | ISSN:1935-5297
July 2013
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