ARBORICULTURE ARBORICULTU & CONTENTS runoff, low infiltration into soil, and URBAN FORESTRY Volume 41, Issue 3, May 2015 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) ® www.isa-arbor.com Sten Gillner, Sandra Korn, and Andreas Roloff Leaf-Gas Exchange of Five Tree Species at Urban Street Sites ................................................... 113 Abstract. For street trees, site-specific soil and microclimate conditions can restrict growth, health, and longevity for many spe- cies. Many urban sites are characterized by a high amount of impervious surface and paved areas resulting in a high rate of sur- face strong reradiation effects. In maintaining the ecologic and economic benefits of ® street trees through future decades, it is essential to establish species with a high tolerance to stressful urban environments. Researchers measured leaf-gas exchange of Acer platanoides, Acer pseudoplatanus, Platanus × hispanica, Quercus rubra, and Tilia platy- phyllos to assess stomatal conductance, transpiration, and net photosynthesis at impervious urban sites in the city of Dresden, Germany. The results show significantly higher leaf-gas exchange rates for the species Platanus × hispanica and Quercus rubra, compared to the spe- cies Acer platanoides and Acer pseudoplatanus. The significantly higher mean values of water-use efficiency of Platanus × hispanica and Quercus rubra, and in particular the values during the selected periods with a high vapor pressure deficit, indicate more economical water consumption. Key Words. Acer platanoides; Acer pseudoplatanus; Climate Change; Dresden; Germany; Leaf-Gas Exchange; Platanus × hispanica; Quercus rubra; Street Trees; Tilia platyphyllos; Urban Trees; Water-Use Efficiency. Gabriel P. Hughes, Clifford S. Sadof, and Matthew D. Ginzel A Borer-Specific Assessment Scheme for Identifying Sentinel Trees to Delimit Invasive Borers in Urban Forests ........................................................................................................................125 Abstract. Aggressive insects like the emerald ash borer [Agrilus planipennis (Fairmaire)] (EAB) increasingly threaten the health of the urban forest. Early detection of exotic wood-boring pests is critical for rapid response efforts, and allows for effective management while populations are relatively low. During street tree inventories, arborists record subjective rankings of tree condition and pest incidence; however, the extent of insect attack is rarely quantified. Moreover, it is unknown how the assessment of tree vigor provided by city foresters during these inventories relates to the likelihood of wood-borer infestation. In this study, researchers developed a borer-specific tree vigor assessment scheme to rapidly evaluate street trees, and to identify when EAB populations begin to grow exponentially based on the health of the forest. This scheme incor- porates common indicators of EAB attack, including canopy thinning and epicormic sprouts, as well as attack by common native wood-boring insects. This scheme was used to track the health of ash trees from 2010 to 2013 in one urban forest with advanced symptoms of EAB decline and one without (Indianapolis and Lafayette, Indiana, U.S., respectively). Trees declined more rapidly in Indianapolis where emergence holes from native borers were positively correlated with EAB in infested areas. Over the course of the study, first detections of EAB occurred on progressively weaker trees at both sites, suggesting that early detection of incipient EAB populations can be improved by surveying apparently healthy trees. Key Words. Agrilus planipennis; Early Detection-Rapid Response; Emerald Ash Borer; Surveys; Tree Inventory; Tree Vigor; Wood Borers. Rebecca W. Dolan Two Hundred Years of Forest Change: Effects of Urbanization on Tree Species Composition and Structure ............................................................................................................................136 Abstract. Despite their importance, the dynamics of urban floras are not well understood, and quantitative historical data are rare. The current study used three data sets for trees in Indianapolis/Marion County, Indiana, U.S., to document change over 200 years to the original beech- maple forest and to examine future implications of contemporary tree planting efforts in light of these changes. Data on tree composition and size collected before significant settlement in the early 1800s are compared with recent surveys of trees in remnant natural areas and with trees found on city streets and rights-of-way. All the species recorded in historical surveys are still present in either remnant natural area forests or among city street trees, but frequencies and sizes have changed, and many additional species are now present. Comparison of the composi- tion of the original forest with current remnants shows a 95% decline of American beech (Fagus grandifolia), the most common species in presettlement forests. Sugar maple (Acer saccharum) has more than doubled in number. Silver maple (Acer saccharinum) is the most important street tree, with eight species of non-native broadleaf trees among the most common on city streets, along with evergreen gymnosperms that are not documented in the presettlement flora. Data for contemporary tree planting efforts in the city show a focus on native species that tar- gets replacement of species that have declined in frequency, especially oaks, in proportions that should be sustainable. Patterns reported here are likely representative of those in many forested areas undergoing land conversion and development, so the findings apply to many cities. Key Words. American Beech; Acer saccharinum; Acer saccharum; Fagus grandifolia; Indiana; Indianapolis; Presettlement Forest; Remnant For- ests; Silver Maple; Sugar Maple; Urban Forest; Witness Trees. ©2015 | International Society of Arboriculture | ISSN:1935-5297
May 2015
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