ARBORICULTURE ARBORICULTU & CONTENTS Abstract. Graſting and budding are URBAN FORESTRY Volume 43, Issue 5, September 2017 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) ® www.isa-arbor.com William R. Jacobi, Ronda D. Koski, and Betsy A. Goodrich Long-Term Fluctuations in Water Status and Crown Dieback of Plains Cottonwood Trees. .........173 Abstract. Plains cottonwood trees (Populus deltoides subsp. monilifera (Aiton) Eckenw.) occur in riparian and urban areas in semi- arid regions of western United States. The amount of water necessary to maintain healthy trees while reducing water use are manage- ment objectives along the High Line Canal in Denver, Colorado, U.S. Canal-flow days, soil moisture, precipitation, cottonwood predawn leaf water potentials (ψpd) and crown dieback were measured annually from 1997–2008. Five key findings were: 1) percent soil mois- ture did not correlate with ψpd, 2) trees became moderately water-stressed (ψpd < -0.3 MPa) and severely water-stressed (< -0.5 MPa) 45 and 51 days aſter canal flow ended, respectively, 3) ψpd of water-stressed trees increased 24–48 hours aſter water was added, 4) only 22% of rain events of 25 mm relieved stressed conditions for seven days, and 5) yearly average autumn and growing season ψpd corre- lated with autumn crown dieback at low soil moisture sites (few canal-flow days), but not at moderate or high sites (more canal- flow days). Trees with ψpd > -0.30 MPa generally had low crown dieback, whereas trees with ψpd < -0.50 MPa exhibited moderate or severe crown dieback. Plains cottonwoods are relatively resilient to single-year drought, and moderately stressed trees may recover and can withstand 25%–40% crown dieback if water is available the following year for >14 days. Irrigation timing and the frequency needed to minimize cottonwood future crown dieback can be obtained from autumn and growing season predawn leaf water potentials. Key Words. Colorado; Cottonwood; Crown Dieback; Mortality; Populus deltoides; Semi-Arid; Water Potential; Water Stress. ® G.M. Moore and P.G. McGarry Investigation of the Potential for Bark Patch Grafting to Facilitate Tree Wound Closure in Arboricultural Management Practice .....................................................................................186 common horticultural techniques, and similar techniques have been successfully used in the management of tree wounds by bridge and approach graſting. The success of bark graſts raises the possibility of using bark patch graſts to span trunk wounds and pruning cuts. Fiſty seedling trees from each of six commonly planted Australian native and exotic species—Acacia dealbata, Banksia integrifolia, Eucalyptus viminalis, Platanus × acerifolia, Quercus robur, and Pinus radiata—had circular plugs of bark removed from their stem using a #3 cork borer (9 mm diameter). The plugs were liſted from the stem and then re-attached at one of four rotations (0, 90, 180, and 270 degrees) to the original cambial orientation in each of the four seasons. While there was no successful re-attachment for Pinus radiata, the data for the successful re-attachment of the other five species showed that the most successful orientation for re-attachment was in the original position (0 degrees); successful attachment did occur at other orientations. The best season for re-attachment was spring, but successful attachment did occur in other seasons; success was lowest when graſting was undertaken in winter. The use of bark patch graſts may provide arborists with an additional method for dealing with large wounds caused by vandalism and accidents, and would be particularly useful ering the wound with a bark patch graſt may conceal if a tree was of special, historic, or environmental significance to the landscape. Cov- the removal of a branch, hide obvious scarring, and at the same time reduce the risk of disease and stress to the tree by closing the wound more quickly than would normally occur due to natural callusing. Key Words. Acacia dealbata; Australia; Banksia integrifolia; Bark Graſting; Callus; Eucalyptus viminalis; Native Tree Species; Pinus radiate; Platanus × acerifolia; Quercus robur; Seasonal Wound Responses; Tree Wound Closure. David L. Mausel Subnivean Survival of Hemlock Woolly Adelgid (Adelges tsugae) in New England ....................199 ©2017 | International Society of Arboriculture | ISSN:1935-5297
September 2017
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