306 Wells et al.: Effects of Planting Depth root flare at grade), 15 cm (6 in) deep-planted (planted with the root flare 15 cm below grade), and 31 cm (12 in) deep- planted (planted with the root flare 31 cm below grade). Replicate blocks were laid out as rows perpendicular to the direction of the slope. Planting holes were dug with a backhoe to roughly twice the width of the root ball. After installation, the planting holes were refilled by hand using original, unamended soil. Newly planted trees were mulched to the canopy edge, and follow- up care consisted of weed control within the mulched rings. No supplemental irrigation or fertilization was applied. Measurement Schedule In May 1997, 6 months after transplant, mean shoot length was measured by averaging the lengths of three randomly selected primary lateral shoots collected at a height of 1.8 to 3 m (6 to 10 ft) above the ground. Mean leaf chlorophyll content was estimated by averaging SPAD meter readings from four randomly selected leaves per tree (Minolta SPAD- 502; Minolta Inc., Tokyo, Japan). Mean individual leaf area was measured by averaging the areas of 10 randomly selected leaves per tree (LI-3100 leaf area meter, Li-Cor Biosciences, Lincoln, NE). At the same time, trees were visually rated by a panel of four tree professionals. Panelists scored each tree for shoot tip dieback, defoliation, chlorosis, and leaf curl. The severity of each condition was scored on a scale of 0 to 3, with a score of 0 indicating that the condition was not present and a score of 3 indicating that the condition was severe. Scores from all panelists were averaged to produce a set of mean scores for each tree. In December 1997, one year after transplant, 4 soil cores (5.1 cm2 [0.82 in2] in diameter, 61 cm [24 in] deep) were obtained from beneath each tree to measure the root mass density (RMD; g root dry weight/cm3 soil volume) and depth distribution of the root system. Two cores were taken 15 cm (6 in) from the trunk (i.e., within the diameter of the origi- nal root ball), and two cores were taken 41 cm (16 in) from the trunk (i.e., outside the diameter of the original root ball). Each core was divided into two depth increments of 30.5 cm (12 in) each. Roots (less than 5 mm/0.2 in diameter) from each depth increment were sieved free of soil and oven-dried for 2 days at 70°C (158°F). For each core, RMD was calculated for the individual depth increments and for the core as a whole. The root depth ratio (RDR) for each core was calculated as the RMD of the upper depth increment divided by the RMD of the lower depth increment. In January 2000, 3 years after transplant, an air compressor with an attached Air SpadeTM (Concept Engineering Group, Inc., Verona, PA) was used to expose the root collars of all remaining trees to assess girdling root development. Girdling roots were defined as woody roots that contacted and en- ©2006 International Society of Arboriculture circled a portion of the stem causing bark and wood com- pression (Johnson and Hauer 2000). Potentially girdling roots were defined as woody roots that crossed within 2.5 cm (1 in) of the stem in a girdling orientation. The percentage of the trunk circumference encircled by girdling and potentially gir- dling roots was recorded for each tree. Tree survival data were analyzed by 2. All other data were analyzed in SAS (SAS Software, Inc., Cary, NC) using PROC GLM; mean separations were performed with Tukey’s HSD. Treatment main effects and dependent multiple com- parisons were evaluated at the 0.05 significance level. Because girdling root data were expressed as percentages, they were arsine transformed before analysis. RESULTS Tree Survival Deep planting had a strong negative effect on the survival of Yoshino cherries. Two years after transplanting, 50% of the 15 cm (6 in) and 31 cm (12.4 in) deep-planted cherries had died, whereas all the control cherries had survived (Figure 1). The majority of these deaths occurred during the second growing season after transplant (i.e., 1998). Survival of maples was not affected by planting depth: mortality among the treatment groups varied from 0% to 10% and did not differ significantly with treatment (Figure 1). After 2 years, no further tree mortality was observed in either species. Above-Ground Measurements In May 1997, 6 months after transplant, there were no treat- ment-related differences in the lengths of individual shoots or the areas of individual leaves for either species. However, 31 cm (12.4 in) deep-planted trees of both species had signifi- cantly lower leaf chlorophyll content as estimated by SPAD meter readings (Table 1). None of the maples showed visible signs of stress at this time, but the 31 cm (12.4 in) deep- planted cherries were rated significantly higher than the con- trols for defoliation, chlorosis, and leaf curl (Table 1). Figure 1. The percentage of trees from control, 15 cm (6 in) deep-planted, and 31 cm (12.4 in) deep-planted treatment groups that survived more than 2 years after transplant. Within a panel, bars marked with an asterisk are significantly different from control (P < 0.001; 2 test).
November 2006
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
