54 Arboriculture & Urban Forestry 2008. 34(1):54–58. Appleton et al.: Tree Stabilization Tree Stabilization: Current Products and Practices Bonnie L. Appleton, Carolyn M. Cannella, P. Eric Wiseman, and Alexis A. Alvey Abstract. Products and systems used to stabilize trees at transplant should be prescribed based on site conditions, tree charac- teristics, and planting and maintenance practices. Alternatives to traditional aboveground trunk staking and guying methods exist, generally consisting of products that anchor tree rootballs rather than supporting tree trunks. When assessing the need for tree stabilization at transplant, several factors should be considered, including material costs, time required for installation and maintenance, product persistence in the landscape, and aesthetics. Key Words. Balled and burlapped (B&B); container-grown; guying; rootball anchoring; staking; transplanting; trunk support. The requirement for some form of tree stabilization is a compo- nent of most landscape tree installation guidelines and specifi- cations. This practice is the subject of ongoing debate and con- troversy within the green industry. Nurserymen, landscape de- signers and architects, landscape contractors and managers, and arborists often disagree about the need for stabilization and the most appropriate products or systems to use. Unfortunately, trees are often the inadvertent victims of these disagreements. When a tree dies as a result of injury from a stabilization product or system, there is often finger-pointing to assign blame. The landscape manager might blame the landscape architect for specifying a system that injured the tree. The ar- borist removing the same dead tree might blame the landscape manager for not removing the system in a timely fashion to prevent injury. Proper prescription of stabilization systems, based on an assessment of site, tree, and management factors, can prevent such conflicts and, more importantly, minimize tree injury. REASONS FOR TREE STABILIZATION For successful establishment, trees must be kept upright and relatively motionless while their roots grow from the rootball into the surrounding soil. Root development includes the plagio- tropic growth of large structural roots along with the lateral growth of small absorbing roots. In time, a sufficient number of roots grow into the soil to anchor the tree. However, excessive tree movement, or repeated blowover, can hamper root develop- ment. Stabilization systems minimize tree movement, facilitating root development and tree establishment. Regardless of tree production and harvest method at the nurs- ery, installation of tree stabilization systems should not be man- dated, but instead a system should be prescribed based on as- sessments of site, tree, and installation and management factors. Systems should be prescribed when one or more of the following conditions threaten the stability of newly planted trees: • Site conditions: strong or unidirectional winds; compacted, wet, or shallow soils; sandy soils; steep slopes; • Tree characteristics: bare root; large or spreading crowns; tall or weak trunks; lightweight rootballs; underdeveloped/ coarse root systems; improperly harvested root systems; im- properly handled rootballs; dormant versus active root sys- tems; ©2008 International Society of Arboriculture • Planting practices: bare root planting; wire basket removal; rootball manipulation; elevated planting in wet soils; • Maintenance practices: use of lawnmowers and string trim- mers close to tree trunks; and • Site uses and problems: playgrounds and recreation fields; high-traffic sidewalks, curbs, and parking areas; tree theft and vandalism. DISADVANTAGES OF TREE STABILIZATION Just as there are compelling reasons to stabilize trees at planting, there are also disadvantages of stabilization systems that are improperly prescribed, installed, or maintained. Some of these disadvantages are: • Detrimental tree growth effects: decreased caliper and trunk taper; increased trunk height; asymmetrical trunk growth; reduced root growth (Harris 1969; Burton and Smith 1972; Wrigley and Smith 1978; Appleton and Whitcomb 1984; Ellyard 1984; Harris 1984; Svihra et al. 1999; Schuch and Kelly 2004); • Hazardous tree growth effects: trunk compression, girdling, or abrasion; development of less trunk flex response to wind (may snap above guying or when guying removed) (Neel 1971; Leiser et al. 1972; Fulmer and Jones 1974); • Aesthetics: unattractive; visually distracting; • Hazards: can cause personal injury or equipment damage; can encourage vandalism; and • Economics: costs for materials or products; installation la- bor; follow-up maintenance to adjust or remove; costs to remove or replace damaged trees. TREE STABILIZATION LITERATURE AND SURVEYS Many new tree stabilization products and systems have been recently introduced, renewing interest in the science and appli- cation of tree stabilization. As part of a research initiative at Virginia Tech, a literature review and manufacturer/practitioner surveys were conducted to better understand the state of knowl- edge on tree stabilization and the availability and use of products and systems in the green industry. Published research on tree stabilization is limited. Neel (1971) showed that motion, light, and growth regulators influenced
January 2008
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