Arboriculture & Urban Forestry 35(6): November 2009 maple trees at the Dublin and Strongsville sites. Approxi- mately 20% of the Dublin trees and 90% of the Strongs- ville trees required removal of potential girdling roots. Parameters Measured To determine the effect of RCE on trees too deep in the soil profile, measurements were made of tree growth, leaf chloro- phyll, stress, and pest activity. To quantify the effect of RCE on growth, four annual measurements were made, including trunk diameter, tree height, canopy width, and twig extension. Trunk diameter was measured at 1.4 m (4.5 ft) above ground [diam- eter at breast height (DBH)]. Height was obtained by measuring the distance from the soil’s surface to highest point on the tallest vertical branch. Canopy width was determined by measuring the distance between the ends of the widest horizontal branches on either side of the tree. For twig extension (growth), twigs were selected at random from the canopy at 1.5 m (5 ft) to 3 m (10 ft) above ground. The current season’s twig extension was ob- tained by measuring the distance between the tip of a twig and the first ring of bud scale scars. Previous year’s twig extension was estimated by measuring the distance between subsequent an- nual bud scale scars. A single growth measurement was taken per tree except twig extension where three measurements were taken and averaged. All growth measurements except twig exten- sion are reported as an increase in growth. Increase in growth was calculated by subtracting the previous year’s total dimension from the current year’s total dimension. For example, if a tree’s height was 7 m (23.1 ft) in 2005 and 8 m (26.4 ft) in 2006, an increase in height of 1 m (3.3 ft) was recorded; and if the same tree was 8.5 m (28.0 ft) in 2007, 0.5 m (1.6 ft) was recorded. To determine the effect of RCE on chlorophyll, leaf chlo- rophyll was measured using a CCM-200 Chlorophyll Content Meter (Opti-Sciences, Hudson, NH). The meter does not di- rectly measure chlorophyll but gives relative chlorophyll val- ues by measuring the amount of energy absorbed in the red light waveband. The readings were taken in summer during July and August. Three leaves per tree were randomly cho- sen from the canopy at 1.5 m to 3 m above ground and mea- sured for chlorophyll with average chlorophyll being reported. During the early summer of 2004, the maples at the Dub- lin location displayed early fall color. The change in leaf color was attributed to transplant shock. The trees were visually rated for fall color on a numeric scale of one to five. A rating of one was assigned to a tree whose leaves had red color and a rating of 5 assigned to leaves having green color. In the late summer of 2007, the shingle oaks at the Cincinnati location showed scorch symptoms due to drought. A visual rating of the scorch was taken on a numeric scale of one to five. A rating of one represented a tree whose leaves were brown in color while a rating of five was leaves with normal green color. Thus with both stress ratings, higher numbers represent healthier trees. Also at the Dublin location, the blue spruce trees expe- rienced infestations of spider mite (Oligonychus ununguis Jacobi) and bagworm (Thyridopteryx ephemeraeformis Ha- worth). For the mites, the trees were visually rated for the percent of foliage discolored by the mite infestation. For the bagworms, a count of the number of bags per tree was taken. 289 Experimental Design and Statistical Analysis The trees at each test site were randomly assigned to one of two treatments. One-half of the trees received RCE while the other half (controls) did not receive RCE. A complete- ly randomized experimental design was used for each site. The measurements were subjected to an analysis of variance [ANOVA (SAS Institute 1990)]. Depending on the site, thir- teen to nineteen total measurements of growth, leaf chloro- phyll, stress, and pest activity were taken from 2004–2007. RESULTS AND DISCUSSION After four years, four of the eight sites showed no differ- ence in growth or leaf chlorophyll between trees receiving the RCE treatment and the control trees. The sites showing no ef- fect from RCE included the Cincinnati shingle oak, Dublin blue spruce, and the Strongsville honeylocust trees (Tables 3–6). Likewise the RCE treatment did not influence drought stress experienced by the Cincinnati shingle oak or spruce mite or bagworm severity for the Dublin blue spruce trees. Response to the RCE treatment was observed at the remaining four sites. At the Dublin location, three growth and chlorophyll measurements (three of 16 total growth, chlorophyll and stress measurements) suggested that maple trees treated with RCE had less growth and chlorophyll than control trees (Table 7). While some responses to RCE occurred for growth and chlorophyll, RCE did not influence the stress measurements taken for the Dublin maple park trees. A similar result occurred at the Strongs- ville location (Table 8) with the hedge maple where control trees had greater twig extension and higher leaf chlorophyll readings (3 of 14 total growth and chlorophyll measurements). The poorer growth and reduced chlorophyll with the RCE treatment may be attributed to the removal of girdling roots present at the time of treatment. Removal of potential stem girdling roots on trees in both communities may have subjected the maples to mois- ture stress causing a reduction in growth rate and chlorophyll. The 2006 chlorophyll measurements for the ash trees at the Dublin location demonstrated greater chlorophyll for the trees that received the RCE treatment when compared to those who did not (Table 9). The 2006 chlorophyll values represent one measurement of 14 total growth and chlorophyll measure- ments made through the experimental period. Likewise for the Cincinnati lacebark elm, trees that received the RCE treat- ment had greater growth (two of 16 total growth and chlo- rophyll measurements) than those that did not (Table 10). Seventy-five percent of the sites showed either no effect or a detrimental effect from the RCE treatment. This occurred in spite of the fact that the trees in this experiment had excessive soil over the root system according to industry standards. Tree disorders frequently take many years to manifest themselves. For example, the constricting effect of girdling roots does not become evident until the trees are in a landscape for three to 15 years (Harris 1992). Perhaps given a longer observation period following the root crown excavation, the impact of RCE would be more evident. ©2009 International Society of Arboriculture
November 2009
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