Arboriculture & Urban Forestry 36(3): March 2010 Arboriculture & Urban Forestry 2010. 36(2): 57–65 57 Transplant Season, Irrigation, and Planting Depth Effects on Landscape Establishment of Baldcypress and Sycamore Donita L. Bryan, Michael A. Arnold, Astrid Volder, W. Todd Watson, Leonardo Lombardini, John J. Sloan, Luis A. Valdez-Aguilar, and Andrew D. Cartmill Abstract. Tree transplanting practices influence plant survival, establishment, and subsequent landscape value. The inability to adequately quantify effects of transplanting practices threatens long-term sustainability of landscape trees. Planting depth [i.e., location of the root collar relative to soil grade (soil surface)], is of particular concern for tree growth, development, and landscape performance. The authors of this study investigated the effects of planting depth and transplant season on landscape establishment of baldcypress [Taxodium distichum (L.) Rich.] and effects of planting depth and irrigation practices on landscape establishment of sycamore (Platanus occidentalis L.). Baldcypress planted above grade had reduced relative growth rate in height and diameter compared to those planted at or below grade during the first growing season, regardless of transplant season. Sycamore trees planted below grade had increased mortality and decreased growth compared to trees planted at grade or above grade, regardless of irrigation treatment. Even though trees of both species were grown under similar conditions, baldcypress was much more tolerant to belowgrade planting than sycamore. We suggest that this is related to the native habitat of both species, where baldcypress is frequently exposed to hypoxic conditions while sycamore is more prevalent on well-drained soils. Thus, it may be important to consider the native habitat of a species when evaluating the effect of planting depth. Key Words. Cultural Practices; Landscape Installation; Platanus occidentalis; Relative Growth Rate; Taxodium distichum. Variability in tree planting and transplanting practices is of partic- ular concern as optimum planting depth may vary among species and ecotypes, and success may be dependent on environmental conditions and subsequent cultural practices (Drilias et al. 1982; Pirone et al. 1988; Browne and Tilt 1992; Ball 1999; Gilman and Grabosky 2004; Arnold et al. 2005; Arnold et al. 2007). Intentional belowgrade planting of trees is typically attributed to one of four reasons: 1) to attain uniform height [e.g., palms (Broschat et al. 2009)], 2) to reduce the need for staking during establishment (Day et al. 1995), 3) to improve access to soil moisture (South 2005), and 4) to avoid root growth conflicts with components of man- made infrastructures in urban landscapes (McPherson et al. 2001). Planting trees too deep may cause significant reductions in tree growth. Arnold et al. (2005) showed that planting the root collar deep (7.6 cm) in dense sandy loam soil resulted in poor growth, possibly as a result of decreased soil moisture and/or oxygen in the rhizosphere. Wells et al. (2006) reported that when balled-and- burlapped Yoshino cherry (Prunus × yedoensis Matsum.) trees were planted with root flares at 15 cm or 31 cm below grade, 50% of the trees died within two years of transplanting, while all trees planted with root flares at grade survived. This was likely due to reduced water infiltration to the root ball and insufficient access to shallow mineral nutrient pools (Wells et al. 2006). Similarly, transplanting container-grown sycamore (Platanus occidentalis L.) trees into field conditions (Boonville fine sandy loam) with the root collars 7.6 cm below grade adversely affected survival and growth (Arnold et al. 2007). Planting trees with root collars above grade may cause significant reductions in tree growth pos- sibly due to a wicking effect of moisture and nutrients from the exposed root ball. However, this may be dependent on other envi- ronmental factors such as soil conditions, as planting above grade may be beneficial to tree growth when soils are prone to anoxic conditions. For example, Arnold et al. (2007) reported that syca- more trees transplanted 7.6 cm above grade had a significantly greater height and trunk diameter after three growing seasons when compared to trees transplanted at grade in a heavy (under- lain by a hard clay pan at 15 to 30 cm depth) sandy loam soil. Successful landscape establishment of trees is also dependent on numerous cultural practices including transplant season and irrigation. The season in which trees are transplanted may affect plant growth, survival, and landscape establishment. In temper- ate climates, transplanting usually takes place during autumn and spring, when soil moisture content is generally high (Richardson- Calfee and Harris 2005). Transplanting in autumn, while the tree is dormant, may allow for root establishment if winter soil temper- atures remain high enough (Richardson-Calfee and Harris 2005). However, transplanting in autumn could also result in low sur- vival as a result of low physiological potential for root regenera- tion and growth when soil temperatures are low (Jenkinson 1980; Larson 1984). Spring planting would ensure soil temperatures are high enough for root growth; however, transplanting in spring when trees are approaching budbreak may result in excessive carbohydrate drain from the roots (Dumbroff and Webb 1978). During tree transplant establishment, soil water content is a determining factor for plant growth and survival (Kozlowski and Davies 1975; Gilman 1990). Establishment, growth, and surviv- al of live oak (Quercus virginiana L.) was enhanced when root zones were maintained at a steady water content, compared to ©2010 International Society of Arboriculture
March 2010
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