Arboriculture & Urban Forestry 36(4): July 2010 Arboriculture & Urban Forestry 2010. 36(4): 183–190 183 Effect of Tree Size, Root Pruning, and Production Method on Establishment of Quercus virginiana Edward F. Gilman, Chris Harchick, and Maria Paz Abstract. Significant differences may exist in establishment rate between trees planted from containers and those from field nursery. Con- tainer-grown plants have root balls with deflected roots which could impact establishment. Slicing root balls at planting could improve post- planting performance of container-grown trees. Sixty live oak 170 L containers were planted into landscape field soil. Root balls from 30 of these containers were sliced prior to planting. Thirty field-grown trees of slightly larger size, and 30 smaller trees from 57 L containers, were also planted. During dry periods in the first 432 days after planting (DAP), 57 L container trees had the least negative xylem poten- tial. Field-grown trees had the most negative xylem potential when irrigation was withheld 12 DAP. Slicing root balls had little impact on xylem water potential in drought. Defoliation was greater for 170 L container trees than for 57 L containers. Trunk diameter increase of 57 L containers and field-grown trees was greater than for 170 L containers. Field-grown trees grew less in height. Root system radius was similar for 170 L containers and field-grown trees, and greater than 57 L containers. Small trees appear to establish quicker than larger trees. Key Words: B&B; Containers; Drought; Field-Grown; Irrigation; Planting; Root Ball; root:shoot Ratio; Transplanting; Tree Survival; Xylem Water Potential. Nearly 300 years ago, nursery operators understood that trees were more likely to establish in a poorly drained soil if a seed was planted direct into soil than if a tree was transplanted from a nursery (Langley 1728). Roots from seeds grown in place re- spond to soil conditions present at the planting site; whereas, roots from a transplanted tree are forced to adapt and adjust to conditions at the planting site. Planting site soil attributes are often different than in the nursery, and this can impact wa- ter relations (Spomer 1980) and root growth (Coutts and Ni- coll 1991), after landscape planting. Trees from certain nursery production methods and trees with sliced root balls at plant- ing may adapt quickly to the new landscape soil environment. Planting seeds into urban landscapes is not practical, at least by way of current urban forestry practices. However, Watson (1985) modeling root growth rates in USDA hardiness zone 5, suggested that small nursery stock (10 cm caliper) would estab- lish and grow quicker than large (25 cm caliper) trees. Gilman et al. (1998) confirmed that small caliper trees (6.3 cm) grew at a faster rate than large trees (10 cm) in the three years after plant- ing from a container, but not when planted from a field nursery. In addition, the smaller field-grown trees were statistically simi- lar in trunk caliper three years after planting to the large con- tainer-grown trees. On the other hand, Struve et al. (2000) found no difference in growth rates between small and large-sized trees. This suggests tree size or age at planting impacts estab- lishment rate in urban landscapes, at least in certain soil types. Trees have been transplanted bare root or with an intact soil ball for hundreds of years (Langley 1728), and probably longer with good success. Trees planted bare root have been shown to grow as well after landscape planting as trees from other nurs- ery production methods (Buckstrup and Bassuk 2000; Anella et al. 2008). Container production has become increasingly popu- lar in the past 50 years, especially in the warmest parts of North America. Many types of containers have been developed for growing trees and shrubs (Appleton 1993). Container type im- pacts post-transplant growth for seedling-sized liners of certain species (Struve 1993), but may not impact larger-sized nursery stock typically planted in urban landscapes (Marshall and Gil- man 1998; Gilman 2001). Various comparisons among nursery production methods including bare-root, container, field-grown balled-and-burlapped (B&B), and in-ground fabric contain- ers were made in the past 30 years measuring transplant sur- vival, water stress after planting, growth rates, and root form. Appropriate irrigation management is often cited as important for trees planted from all production methods due to inadequate rainfall to maintain turgor after planting. Freshly dug field-grown B&B East Palatka holly (Ilex x attenuata ‘East Palatka’) trees were more stressed and more likely to die than trees planted from containers if they were not regularly irrigated after transplanting due to the sudden loss of roots (Harris and Gilman 1993). Howev- er, with regular irrigation, laurel oak (Quercus laurifolia) and East Palatka holly trees from either production method experienced similar post-transplant water stress (Gilman and Beeson 1996). Ir- rigating newly planted trees not only improved their survivability and growth but lead to better branch structure (Martin and Stutz 1994; Struve 1994). More rapid root growth from well-watered field-grown B&B laurel oak trees resulted in faster establishment than trees planted from containers filled with bark:peat:sand sub- strate. Beeson and Gilman (1992) proposed that field-grown live oak trees may osmotically adjust when roots were severed, helping ©2010 International Society of Arboriculture
July 2010
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