66 Arnold et al.: Below-Grade Planting Affects Survival and Growth Table 1. Three-year survival and growth increment of five taxa grown for 3 years in a field site in College Station, Texas, after transplant from 9.3 L (#3) black plastic containers. Taxaz Lagerstroemia Fraxinus Nerium Platanus Vitex Planting depthy Below grade At grade Above grade Below grade At grade Above grade Below grade At grade Above grade Below grade At grade Above grade Below grade At grade Above grade Survival (no. out of 6) 4 6 6 3 6 6 4 6 6 3 5 6 6 6 6 Height (cm) 136 ± 26x 185 ± 21 176 ± 21 138 ± 30 170 ± 21 194 ± 21 98 ± 26 121 ± 21 145 ± 21 212 ± 26 183 ± 23 257 ± 23 135 ± 21 152 ± 21 150 ± 21 occidentalis, and Vitex agnus-castus ‘LeCompte’. yRoot collar placed at grade or 7.6 cm (3 in) above or below grade. xValues represent the means (± standard errors) of six plants per taxa and planting depth combination. eter, and cross-sectional areas for years 2 and 3. For instance, adjusted trunk diameter growth rate year 2 (in units of mil- limeters incremental diameter per millimeter starting diam- eter)[(trunk diameter year 2 – trunk diameter year 1)/trunk diameter year 1]. Data were analyzed using the fixed-effects general linear models procedures in the SAS System for Win- dows, Release 9.1 (SAS Institute, Inc., Cary, NC). RESULTS AND DISCUSSION Survival after 3 years was nearly 100% for all species when planted at or above grade; however, when planted below Table 2. Analysis of variance effects significance for 3 year survival, height, total cross-sectional trunk area, and trunk diameter five taxa grown for 3 years in a field site in College Station, Texas, after transplant from 9.3 L (#3) black plastic containers. Analysis of variance effects Taxaz Planting depthy Survival Height NSx *** Taxa × planting depth NS NS Cross- sectional area *** * * *** NS Trunk diameter ** * NS zFive taxa included Lagerstroemia indica x Lagerstroemia fauriei ‘Basham’s Party Pink’, Fraxinus pensylvanica, Nerium oleander ‘Cranberry Cooler’, Platanus occidentalis, and Vitex agnus-castus ‘LeCompte’. yRoot collar placed at grade or 7.6 cm (3 in) above or below grade. x*, **, ***, NS indicates statistical significance of the effect at P 0.05, P 0.01, P 0.001, or not significant, respectively. ©2007 International Society of Arboriculture grade, survival was reduced for all species except vitex (Tables 1 and 2). Planting above grade did not affect survival rates relative to those planted at grade, except for sycamore, which actually survived in higher numbers when planted above grade than at grade (Table 1). With the exception of sycamore, which was significantly taller when planted above grade than at grade, planting above grade yielded similar heights as planting at grade (Tables 1 and 2). Planting below grade reduced the height growth of all taxa but sycamores. Below-grade planting reduced cross-sectional trunk area and trunk diameter of all taxa except sycamore, which had a smaller cross-sectional area and trunk diameter both below and at grade compared with above-grade planting (Tables 1 and 2). Oleanders that survived 3 years increased little in Table 3. Effect of planting depth on the plant index of Nerium oleander ‘Cranberry Cooler’ grown for 3 years in a College Station, Texas, field site after transplant from 9.3 L (#3) black plastic containers. Planting depthz Below grade At grade Above grade (m3 ) 0.47 bx 1.39 b 2.37 a zRoot collar 7.6 cm (3 in) below grade, at grade, or 7.6 cm (3 in) above grade. yHeight × diameter within row × diameter between rows representing a volumetric estimate of the canopy. xMeans followed by the same letter are not significantly different (P 0.05) using least squares means comparisons. Values represent the means of six plants per planting depth. Plant indexy Cross-sectional area (cm2 ) 3.9 ± 2.6 10.3 ± 2.2 12.9 ± 2.2 2.6 ± 3.2 4.9 ± 2.2 4.2 ± 2.2 3.1 ± 2.8 6.8 ± 2.2 13.2 ± 2.2 6.3 ± 2.8 6.0 ± 2.5 13.6 ± 2.5 7.8 ± 2.2 11.4 ± 2.2 12.0 ± 2.2 Trunk diameter (mm) 19.4 ± 4.5 22.8 ± 3.7 25.7 ± 3.7 17.4 ± 5.2 24.8 ± 3.7 22.9 ± 3.7 12.1 ± 4.5 21.2 ± 3.7 18.4 ± 3.7 26.6 ± 4.5 25.8 ± 4.0 40.5 ± 4.0 17.6 ± 3.7 23.6 ± 3.7 25.6 ± 3.7 zFive taxa included Lagerstroemia indica × Lagerstroemia fauriei ‘Basham’s Party Pink’, Fraxinus pensylvanica, Nerium oleander ‘Cranberry Cooler’, Platanus
January 2007
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