4 Gilman: Anchorage Influence by Production Method and Root Pruning Table 3. Effect of root pruning at planting on bending stress required to pull trunks to various trunk angles seven months later. Root pruning Bending stress to 5 degrees (kN/m2 Yes No 32953 (1276) az 29531 (1852) a ) Bending stress to 10 degrees (kN/m2 42851 (1692) a 37597 (1361) b z Means (with S.E.) compared within a column (P < 0.03), based on 12 trees per treatment. and Owens 2000). Tree size, cultural conditions, soil, weather, species, and other factors likely account for the variety of results. Root pruning at planting improved anchorage as shown by the approximate 13% increase in bending stress required to pull trunks to 10 degrees (Table 3). There was no difference when trees were pulled to 5 (P = 0.1) or 15 (P = 0.31) degrees. This suggests that there may be an enhancement of anchorage as a result of root pruning (described as shaving) at planting as found by Gilman and Wiese (2012) on smaller trees (57 L) of the same species. Shaving the root ball increased stability without reducing survival, crown appearance (not measured), or growth (Table 2). Shaving has also been shown to remove most circling roots at the periphery of the root ball (Gilman and Wiese 2012), thus reduc- ing the likelihood of developing stem girdling roots in the future. Trees had a statistically (Table 2) larger trunk diam- eter (107 mm) when irrigation was directed only onto the root ball surface than when irrigation was applied to the root ball plus the area around it (104 mm). The difference in size was obviously very small and probably not biologically sig- nificant or meaningful. There was no apparent explanation for the increase in trunk growth associated with less irriga- tion unless the soil remained too wet, which is not common in this soil type. Water was never seen standing in the field and similar studies showed either more growth (Stabler and Martin 2000; Montague et al. 2007) or no impact of increas- ing irrigation volume (Gilman et al. 1998; Wiese et al. 2009). Bending stress was also not impacted by irrigation (Table 2). Although irrigation placement was confounded with irriga- tion volume in the current study (i.e., double the volume was applied in the larger application area), Gilman et al. (2002) found that neither irrigation placement (close to the trunk ver- sus over a larger area) nor volume affected growth or post- digging survival. Beeson and Gilman (1995) also found that irrigation placement had no impact on shoot or trunk growth or root mass (roots < 10 mm diameter) within or beyond the irrigated soil area. All shrub species tested also generated roots in the soil well beyond the irrigated zone when water was applied only on the root ball (Shober et al. 2009). Along with the current data, these studies collectively support the notion that irrigation application outside the root ball has little im- pact on growth rate or anchorage of woody plants in this soil type. Research in other regions is incomplete, making it dif- ficult to extrapolate results to other soil types and climates. Results might have been different in drier weather, for differ- ent species, or in a drier climate in sites without irrigation. CONCLUSIONS Trees with a 14 cm trunk diameter from a field nursery were better anchored to the soil seven months after planting than identically sized trees from containers. However, anchorage can be improved by shaving off the periphery of the container root ball at planting without sacrificing survival or trunk diameter growth. Longer- ©2013 International Society of Arboriculture term studies are encouraged on large trees to determine if results from these short-term studies apply in the long run. Irrigation placement had little impact on growth or anchorage after planting. LITERATURE CITED Arnold, M.A. 1996. Mechanical correction and chemical avoidance of circling roots differentially affect post-transplant root regeneration and field establishment of container-grown Shumard oak. Journal of American Society Horticultural Science 121:258–263. Beeson, Jr., R.C., and E.F. Gilman. 1992. Diurnal water stress during landscape establishment of slash pine differs among three production methods. Journal of Arboriculture 18:281–287. Beeson, Jr., R.C., and E.F. Gilman. 1995. Irrigation and fertilizer place- ment affect root and canopy growth of trees produced in in-ground fabric containers. Journal of Environmental Horticulture 13:133–136. Coutts, M.P. 1986. Components of tree stability in Sitka spruce on peaty, gley soil. Forestry 59:173–197. Coutts, M.P., C.C.N. Nielson, and B.C. Nicoll. 1999. The development of symmetry, rigidity, and anchorage in the structural root system of conifers. Plant and Soil 217:1–15. Gilman, E.F. 2001. Effect of nursery production method, irrigation, and inoculation with mycorrhizae-forming fungi on establishment of Quercus virginiana. Journal of Arboriculture 27:30–39. Gilman, E.F., A. Stodola, and M.D. Marshall. 2002. Root pruning but not irrigation in the nursery affects live oak root balls and digging survival. Journal of Environmental Horticulture 20:122–126. Gilman, E.F., and C. Wiese. 2012. Root pruning at planting and planting depth in the nursery impact root system morphology and anchorage. Arboriculture & Urban Forestry 38(5):229–236. Gilman, E.F., and F.J. Masters. 2010. Effect of tree size, root pruning, and production method on root growth and lateral ability of Quercus virginiana. Arboriculture & Urban Forestry 36:281–291. Gilman, E.F., C. Harchick, and M. Paz. 2010a. Effect of tree size, root pruning, and production method on establishment of Quercus virgin- iana. Arboriculture & Urban Forestry 36:183–190. Gilman, E.F., G.W. Knox, C. Neal, and U. Yadav. 1994. Micro-irrigation affects growth and root distribution of trees in fabric containers. Hort- Technology 4:43–45. Gilman, E.F., M. Paz, and C. Harchick. 2010b. Root ball shaving im- proves root systems on seven species in containers. Journal of Envi- ronmental Horticulture 28:13–18. Gilman, E.F., R.J. Black, and B. Dehgan. 1998. Irrigation volume and frequency and tree size affect establishment rate. Journal of Arbori- culture 24:1–9. Gilman, E.F., T.H. Yeager, and D. Weigle. 1996. Fertilizer, irrigation and root ball slicing affects Burford holly growth after planting. Journal of Environmental Horticulture 14:105–110. Harris, R.W., W.B. Davis, N.W. Stice, and D. Long. 1971. Influence of transplanting time in nursery production. Journal of American Soci- ety Horticulture Science 96:109–110. James, K.R, and B. Kane. 2008. Precision digital instruments to measure dynamic wind loads on trees during storms. Agricultural and Forest Meteorology 148:1055–1061. ) Bending stress to 15 degrees (kN/m2 45681 (2134) a 41882 (2419) a )
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