168 Sydnor and Subburayalu: Expected Environmental Benefits When Planting Larger or Smaller Tree Species? cultivars were originally selected by the nursery industry for marketing traits—such as foliage color in the case of Sunburst honeylocust—but overall growth between cultivars within the genus were similar both in the street trials and the research plots (Sydnor et al. 2010). Thus the honeylocust cultivar, Sunburst, was selected to represent a larger tree for the purpose of the study. Overall, hawthorns had much poorer survival rates in the original OSTEP plantings than honeylocusts, with many haw- thorn plantings in the street trials having no survivors after 35 years. However, site conditions were often poorer for haw- thorns, which were often planted in smaller tree lawns or side- walk cuts or had overhead utility lines that would confound comparisons of growth rate and survival for any species. Lavalle hawthorn had the best survival rates in its genus (Sydnor et al. 2010) and was selected as the subject of this study to represent smaller trees. Additionally, community, site similarities, tree maintenance programs, and growing conditions within the com- munity were considered when selecting representative species. Site Selection Two of the 97 plantings in the community portion of the original OSTEP in Brooklyn, OH, were selected for evaluation because of the previously noted site similarities. The Lavalle hawthorn planting was on Orchard Grove Ave. between Parkside and W. 74th St. (Latitude N41°26’3.60” and Longitude W81°44’50.94”). Hawthorns were planted 12–15 m on center in 2.1 m tree lawns on both sides of the road and estimated to have been planted in 1964 as 5 cm trees. A planting of Sunburst honeylocust was lo- cated on Morton Avenue between Forest Edge Drive and Outlook Drive (Latitude N41°26’45.35” and Longitude W81°44’11.22”). Honeylocusts were planted 12–15 m on center in a 2.4 m tree lawn on both sides of Morton Avenue with an estimated plant- ing date of 1964 and estimated size at planting of 5 cm. Homes, tree lawn sizes, building setbacks, and lot sizes on Or- chard Grove and Morton were similar, and the two sites are locat- ed approximately 1.6 km apart. Soils were urban complexes of a relatively recent geological origin. Soils on Orchard Grove were an Urban land-Elnora complex (UeA), while soils on Morton were Hornell-Urban land complex (HsC) with urban soils representing 30%–70% of the complexes. Tree maintenance during the ensu- ing years was performed by Brooklyn city crews as dictated by city maintenance procedures and thus similar. Homeowner main- tenance varied as would be expected. Sidewalk repair was more common with the larger growing honeylocusts. One homeowner with honeylocust noted that the sidewalk had been repaired twice since she had lived at her home. The tree lawn widths allowed for root pruning to replace sidewalks without affecting structural stability, in the researchers’ judgment. Overhead utility lines were not present in either site, thus no utility pruning was evident. laser rangefinder (Laser Technology, Centennial, Colo- rado, U.S.), in feet. Branch spread was measured along the axis of the road using the same laser rangefinder. The survival rate was estimated by dividing the number of surviving trees by the esti- mated number of possible planting sites in 2007 and in 2009. Ob- vious replacement trees and open sites were counted as missing for the purpose of determining survival rates on the two streets. Morton Ave. contained 75 trees from the original plant- ing while Orchard Grove had only 11. Thus ten trees from each population of trees on the two streets were se- lected at random for inclusion in the study and analysis. The algorithms in i-Tree Streets use look-up tables in size ranges and were too coarse to discern differences since differ- ences in diameter were small as a result of site uniformity (Table 1). Environmental benefits were plotted and the underlying algo- rithms were recovered and used to evaluate the trees individually in each of the two planting sites in Brooklyn, OH, and to describe and quantify the values of environmental and aesthetic benefits. On, Morton Ave. 75 Sunburst honeylocust trees of the orig- Analysis Procedure Comparison of benefits was based on the measurements of DBH made in 2009. Trunk diameter was measured with a diameter tape in inches at 1.3 m. Height and branch spread were measured in feet in 2009. Height was measured using a Model 200, Tru- Pulse™ inal 84 trees had an estimated survival rate of 89%. While on Orchard Grove, only 17 trees appear to have been planted and 11 still remain, giving a 65% survival rate for hawthorn. The survival rates for honeylocusts are similar to six other honey- locust sites in the OSTEP study (avg. 76%). Survival rate for the Lavalle hawthorn on Orchard Grove was higher than in five other sites (avg. 31%) but this was the only site with simi- lar site conditions to the larger growing honeylocusts (Sydnor, et al. 2010). Thus individual i-Tree Streets calculations, using the recovered algorithms were adjusted to 89% survival (multi- plied by 0.89) for trees for Morton Ave. and 65% for Orchard Grove trees, accounting for the different survival rates for the two species and sites over the 46 years since the initial plantings. A two sample t-test was performed on the computed environ- mental benefits for each tree species to test for significance be- tween larger and smaller trees using Minitab 15 (Minitab, Inc., State College, Pennsylvania). An alpha level of 0.05 was used. RESULTS AND DISCUSSION Observations In U.S. studies, when residents were asked about character- istics they value in their street trees, respondents suggested characteristics associated with larger trees, such as the abil- ity to canopy the street and shade their homes (Schroeder and Table 1. Height, caliper and spread of two tree species planted in Brooklyn, OH, after 46 growing seasons in the landscape. A random sample of ten trees was measured for each of the two sites. Caliper cm (in) Mean Std error 34.5 (13.6) 6.2 (2.4) Hawthorn Height m (ft) 7.4 (24.3) 1.0 (3.3) Spread m (ft) 7.7 (25.3) 1.1 (3.6) Caliper cm (in) 51.5(20.3) 2.8 (1.1) Honeylocust Height m (ft) 15.3 (50.2) 1.4 (4.6) Spread m (ft) 13.7 (45.0) 1.1 (3.6) ©2011 International Society of Arboriculture
July 2011
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