ARBORICULTURE ARBORICULTU & CONTENTS URBAN FORESTRY Volume 41, Issue 4, July 2015 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) ® www.isa-arbor.com Linda Chalker-Scott Nonnative, Noninvasive Woody Species Can Enhance Urban Landscape Biodiversity .................173 Abstract. Increasingly, homeowner associations and municipalities are requiring a certain percentage of native trees and shrubs as part of any new landscape installation. These native species mandates make numerous claims as to the superiority of native plants over intro- duced species, including their ability to enhance ecosystem biodiversity. In contrast, nonnative trees and shrubs are labeled as harm- ful to biodiversity, primarily because they are improperly grouped with known invasive species. This review summarizes the current published science regarding the effects of native and nonnative woody species on urban landscape stability as measured by biodi- versity of associated plants, birds, insects, reptiles, and mammals. The preponderance of studies demonstrate that parameters other than species nativity have the greatest influence on biodiversity of these groups. Rather than limiting tree and shrub selection lists to a narrow palette of native species, a more practical, science-based approach to enhancing urban landscape biodiversity is suggested. Key Words. Alien Species; Biodiversity; Botanical Gardens; Golf Courses; Home Gardens; Native Species; Nonnative Species; Planting Man- dates; Public Parks; Residential Landscapes. ® Tim Delshammar, Johan Östberg, and Cecilia Öxell Urban Trees and Ecosystem Disservices—A Pilot Study Using Complaints Records from Three Swedish Cities .................................................................................................................187 Abstract. Past research on urban ecosystem performance has focused mainly on ecosystem services, rather than disservices. How- ever, to justify and fully utilize urban ecosystems, it is important also to assess and minimize the disservices they provide. The aim of this pilot study in Sweden was to contribute to the emerging understanding of urban ecosystem disservices. The central research question focused on how complaint/comment recordings at municipal park departments could be used as a source of knowl- edge on urban tree disservices. Records obtained from the municipal park departments in the three largest cities in Sweden pro- vided evidence of several types of disservices. However, they also had obvious shortcomings that would need to be resolved before they could be used more widely as a source of information on ecosystem disservices. Suggestions for improving the data are provided. Key Words. Municipal; Public Opinion; Sweden; Urban Tree Management. Duncan Slater and Roland Ennos The Level of Occlusion of Included Bark Affects the Strength of Bifurcations in Hazel (Corylus avellana L.) .....................................................................................................194 Abstract. Bark-included junctions in trees are considered a defect as the bark weakens the union between the branches. To more accurately assess this weakening effect, 241 bifurcations from young specimens of hazel (Cor- ylus avellana L.), of which 106 had bark inclusions, were harvested and subjected to rupture tests. Three- point bending of the smaller branches acted as a benchmark for the relative strength of the bifurcations. Bifurcations with included bark failed at higher displacements, and their modulus of rupture was 24% lower than nor- mally formed bifurcations, while stepwise regression showed that the best predictors of strength in these bark-included bifurcations were the diameter ratio and width of the bark inclusion, which explained 16.6% and 8.1% of the vari- ability, respectively. Cup-shaped, bark-included bifurcations where included bark was partially occluded by xylem were found, on average, to be 36% stronger than those, where included bark was situated at the bifurcation apex. These findings show that there are significant gradations in the strength of bark-included bifurcations in juvenile hazel trees that relate directly to the level of occlusion of the bark into the bifurcation. It therefore may be possible to assess the extent of the defect that a bark-included bifurcation represents in a tree by assessing the relative level of occlusion of the included bark. Key Words. Bifurcation; Corylus avellana; Hazel; Included Bark; Rupture Tests; Three-Point Bending. ©2015 | International Society of Arboriculture | ISSN:1935-5297
July 2015
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