Journal of Arboriculture 31(4): July 2005 193 2001 and 2002. Heights were measured with a clinometer at a distance of 15 m (50 ft) from the tree trunk base. Canopy and trunk diameters were measured with a steel tape. Additionally, during August 2002, counts of mortality that had occurred during the two years of study were made. Physiology During April and August 2002, measurements of leaf gas exchange were made using a 1/4 L (1/2 pt) chamber attached to a portable photosynthesis system (LI 6200, LI-COR Biosciences, Inc., Lincoln, NE). Gas exchange measurements were made on recently physiologically mature, sun-adapted leaves under seasonally clear and calm weather conditions from early morning (0700 hr) to late morning (1100 hr) on consecutive days following the protocol of Martin and Stabler (2002) as the expected times for maximum carbon assimila- tion by landscape trees in central Arizona for those times of year. Photosynthetically active radiation during the morning measurements ranged from 650 to 1940 µmol/m2 /s. At each parking lot, measurements were replicated on four widely distributed leaves of six trees per parking lot location (landscaped median and perimeter areas). Gas exchange of trees in only one parking lot was measured each day, and measurements of median and perimeter trees were alternated throughout the sample period each day. Measurements of leaf chlorophyll concentration were also made for all trees during April and August 2002. For Australian bottle tree, Arizona ash, and Chinese elm, estimates of leaf chlorophyll levels were made by ran- domly sampling 28 fully expanded sun leaves per each of six trees per planting location using a SPAD 502 meter (Minolta Camera Co., Osaka, Japan). Actual chlorophyll concentrations were estimated from simple regression models of SPAD values to actual chlorophyll concentra- tions (R2 values ranged from 0.86 to 0.98) for each tree species using the chlorophyll extraction and determina- tion method described by Arnon (1949). Use of the SPAD 502 meter was not possible for Argentine mesquite because it has finely divided, pinnately compound leaves. Instead, ten leaflets from ten fully expanded sun leaves per planting location were randomly harvested and chlorophyll was extracted and measured (Arnon 1949). Statistical Analysis A general linear model procedure (SAS version 6.03, SAS Institute, Cary, NC) was used to compare effects of parking lot location (median verses perimeter location as independent variables) on tree size (2001 and 2002) and physiological (April and August 2002) data. The data for each tree species were initially pooled for analysis of the effect of parking lot location on tree function. Subse- quently, analyses of dependent variable responses to parking lot location were made separately for each tree species. Significance probabilities and F ratios for location effects by species were generated by an analysis of variance (ANOVA) that were calculated using Type IV sums of squares (Milliken and Johnson 1984) because of an unequal number of dependent variable observations per independent treat- ment variable. For each tree species, treatment means for size by year and physiological function by time of year were separated statistically using Fisher’s LSD test at P ≤ 0.05. RESULTS Size Generally, trees located within the landscaped medians were smaller than those located within landscaped areas along the parking lot perimeter, although the extent and signifi- cance of this difference was species specific (Table 1). Australian bottle trees in landscaped medians had signifi- cantly less dbh than those in perimeter landscaped areas both years. In 2002, height of bottle trees in landscaped medians was also significantly less than those in perimeter landscaped areas. Canopy diameters of bottle trees in both median and perimeter locations were statistically similar. Arizona ash and Chinese elm in landscaped medians had significantly less height, dbh, and canopy diameter than those in perimeter Table 1. Effects of landscape median and perimeter planting locations in commercial parking lots on height, diameter at breast height (dbh), and canopy diameter of four landscape tree species in the Phoenix, Arizona, metropolitan area, in 2001 and 2002. 2001 Landscape tree species Australian bottle tree Height (m) Dbh (cm) Canopy diameter (m) Arizona ash Height (m) Dbh (cm) Canopy diameter (m) Argentine mesquite Height (m) Dbh (cm) Canopy diameter (m) Chinese elm Height (m) Dbh (cm) Values are treatment means, for Australian bottle, tree n = 5; for Arizona ash, n = 9 perimeter or n = 10 median; for Argentine mesquite, n = 10; for Canopy diameter (m) z Chinese elm, n = 27 perimeter or n = 33 median. y Treatment means followed by the same letter within rows by year are not significantly different, Fisher’s LSD test, α = 0.05. ©2005 International Society of Arboriculture Median Perimeter 5.8z ay 7.1 a 19.3 b 27.4 a 4.7 a 5.7 a 6.1 b 8.9 a 17.8 b 30.6 a 6.0 b 9.4 a 6.1 a 6.9 a 15.8 a 19.7 a 7.5 b 9.2 a 4.7 b 7.9 a 10.8 b 21.0 a 5.3 b 9.4 a 2002 Median Perimeter 6.2 b 8.7 a 19.7 b 28.2 a 6.0 a 7.7 a 6.3 b 8.5 a 18.0 b 31.7 a 6.0 b 10.2 a 6.5 a 8.0 a 16.7 b 22.0 a 8.7 a 9.7 a 4.7 b 7.9 a 11.2 b 21.2 a 5.2 b 9.1 a
July 2005
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