ARBORICULTURE ARBORICULTU & CONTENTS URBAN FORESTRY Volume 42, Issue 1, January 2016 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) ® www.isa-arbor.com Alisha M. Autio and Michael E. Day Cytokinin Phytohormonal Effects on Crown Structure ..................................................................1 Abstract. This literature review explores the relevance of cytokinins to tree canopy form, integrating scientific research with current and potential applications to tree care methods. Current and most popular tree care methods call for growers to physically alter the shape of a tree by staking, pruning, and pinching, which can be time-consuming and expensive. Application of phytohormones (also known as plant growth regulators, PGRs) can provide ornamental growers and arborists with alternative methods to manipulate tree crown characteristics. Following a digest of the science of cytokinin activity, the review investigates the current and potential uses of phytohormones as a cost-effective, alternative method of manipulating tree shape. It discusses how the different forms of cytokinin PGRs, acting alone and in concert with other PGRs, can be used, what they can be used for, methods of application, and timing of applications within the phenological cycles of trees. By integrating current basic and applied literature, the review seeks to summarize understanding of cytokinin regulation of crown structure, while exploring potential applications in the tree care industry. Key Words. Branching; Bud Formation; Crown Alteration; Cytokinin; Plant Growth Hormones; Plant Growth Regulators; Tree Physiology. ® Johan Östberg and Johan Sjögren The Linear Index of Tree Appraisal (LITA) Model for Economic Valuation of Large Urban Trees in Sweden ...................................................................................................................................21 Abstract. Economic valuation of urban trees is important for their management and to ensure that such trees are maintained and protected. However, numerous models for valuing urban trees are currently available, which has led to great variation in the final price. It has also resulted in multiple models being used within the same country, thus confusing the courts. Against this background, researchers examined whether the horizontal cross-sectional area of the tree should be used as the basis for extrapolating tree replacement cost in a linear fashion. Researchers also developed a model, the Linear Index of Tree Appraisal (LITA) model, which uses tree cross-sectional area to extrapolate from a band of known prices to a base price for any desired tree size, which can then be adjusted using an appropriate factor depending on tree vitality/damage. The LITA model is easy to use and to update, does not have any limitations concerning tree species or sizes, and does not rely on subjective judgments except in assessment of tree damage. It provides a simple method for determin- ing the replacement cost of urban trees and is thus designed to work where ‘soſt’ values are sometimes difficult to justify. Key Words. Appraisal; Management; Scandinavia; Sweden; Tree Valuation; Urban Trees. Edward F. Gilman, Maria Paz, and Chris Harchick Effect of Eight Container Types and Root Pruning During Nursery Production on Root Architecture of Acer rubrum ........................................................................................................31 Abstract. There is a general understanding that roots deflect when striking solid nursery container walls, and that on trees with good vital- ity this occurs within weeks of shiſting into larger containers. Root architecture is poorly understood when observed in containers with walls constructed of porous plastic and of materials other than plastic. The objective of this study was to measure impacts of container type, root pruning when shiſting to a larger container, and cardinal direction on root architecture in nursery containers up to the #45 size (approximately 170 L). Trunk diameter in #45 containers varied less than 5 mm among eight container types and was not impacted by root pruning. More root growth occurred in the northern than southern half of containers. Container type had a small impact on root architecture; in contrast, root pruning by shaving the periphery of the root ball at each shiſt had a large impact. Shaving when shiſting dramatically reduced the per- centage of trees graded as culls and suppressed stem-girdling root formation compared to not shaving. Shaving shiſted deflected woody root mass from the interior of the root ball to the exterior, making it simple to remove peripheral roots when planting into the landscape. Key Words. Acer rubrum; Circling Roots; Containers; Descending Roots; Porous-Walled Containers; Red Maple; Root Collar; Shaving; Solid- walled Containers; Straight Roots. ©2016 | International Society of Arboriculture | ISSN:1935-5297
January 2016
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