194 Celestian and Martin: Parking Lot Location Effects on Trees landscape beds both years. Argentine mesquite in landscaped medians had significantly less canopy diameter in 2001 and less dbh in 2002 than those in perimeter landscaped areas. Argentine mesquite height was not affected by parking lot location. During the study, two Argentine mesquite trees in the parking lot medians were removed because of wind damage caused by intense monsoon storms during summer 2001. Otherwise, no tree mortalities occurred. Physiology Australian bottle tree leaf net photosynthesis (A), stomatal conductance (gs ), and chlorophyll concentration were of median trees was not statistically different than that of perimeter trees. In April, leaf chlorophyll concentration of bottle trees within the landscaped medians was 9% greater than it was for trees within the perimeter areas. In August, however, this trend was reversed and leaf chlorophyll concentration of perimeter trees was 7% greater than it was for trees within the landscaped medians. Parking lot location had no statistical effect on the ratio of internal leaf mesophyll to ambient air CO2 bottle trees in landscaped medians were about 36% and 27%, respectively, less than leaves of those in perimeter landscaped areas (Table 3). However in August, leaf A of perimeter trees was 9% greater than that of median trees, while leaf gs concentration (Ci/Ca) of bottle trees, though Ci/Ca values were 11% higher in April than they were in August. For Arizona ash, leaf A and Ci/Ca were affected by an interaction of time of year and parking lot location (Table 2). Leaf A of ash trees in the landscaped perimeter areas was not statistically different than that of median trees in April but was about 60% greater than that of median trees in August (Table 3). The Ci/Ca of ash trees was not affected by parking lot location in April but was about 8% greater than that of perimeter trees in August. Ash leaf gs concentration were about 50% and 20% higher in August than April, respectively, and 35% and 10% higher for perimeter trees than median trees, respectively (Table 3). For Argentine mesquite, only leaf chlorophyll concentra- tion was affected by an interaction of time of year and parking lot location (Table 2). In April, leaf chlorophyll concentration of perimeter trees was about 30% greater than it was for median trees, but was not affected by parking lot location in August (Table 3). Mesquite leaf A and Ci/Ca were greatest in April, and gs Mesquite leaf A, gs concentration were not affected by an interaction of time of year and planting location (Table 2). Leaf gs was greatest in August. concentration were all affected by an interaction of time of lot location (Table 2). For Chinese elm, leaf A, gs ©2005 International Society of Arboriculture , and Ci/Ca were not affected by parking , Ci/Ca and chlorophyll and chlorophyll and chlorophyll affected by an interaction of time of year (April and August) and parking lot location (Table 2). In April, leaf A and gs of DISCUSSION Asphalt is the dominant surface component of commercial parking lots. Consequently, trees in commercial parking lot landscapes must contend with an array of environmental stress factors related to the thermophysical characteristics of asphalt paving and limited belowground growing space (Celestian and Martin 2004; Grabosky and Gilman 2004). After 2 years of study, we found that the size and physiologi- cal health of trees located in narrow landscaped medians surrounded by asphalt paving tended to be less than for Table 2. Significance probabilities and F ratio gener- ated by an analysis of variance (ANOVA) of the effects of commercial parking lot planting location (landscape median and perimeter) and time of year (April and August 2002) on leaf gas exchange [net carbon assimi- lation (A), stomatal conductance (gs ambient CO2 ), internal leaf to concentration (Ci/Ca)] and leaf chlorophyll concentration (Chl) of four landscape tree species in Phoenix, Arizona. Tree species/ANOVA A Australian bottle tree Location Time of year Location × time F ratio Arizona ash Location Time of year Location × time F ratio Argentine mesquite Location Time of year Location × time F ratio Chinese elm Location Time of year Location × time F ratio gs Ci/Ca Chl 0.0001 0.0147 0.3238 0.0001 0.0001 0.0001 0.0092 0.0001 0.0001 0.0001 0.1639 0.0001 23.45 17.48 12.09 7.41 0.0001 0.0001 0.0001 0.0001 0.2433 0.0001 0.0001 0.0001 0.0191 0.1012 0.0001 0.3351 18.88 52.15 177.78 11.92 0.0930 0.0614 0.1910 0.0001 0.0041 0.0001 0.0001 0.4340 0.2367 0.0652 0.1638 0.0077 10.45 9.96 97.88 2.96 0.0009 0.8806 0.0561 0.0001 0.0001 0.8776 0.0001 0.0001 0.0061 0.0004 0.0002 0.0008 9.81 6.15 16.26 9.39 year and parking lot location (Table 2). Leaf A and chloro- phyll concentration of perimeter trees were 6% and 14% greater, respectively, than that of median trees in April, but 21% and 25% greater, respectively, than that of median trees in August (Table 3). Leaf gs 11% and 5% greater, respectively, than that of median trees in August. 9% and 4%, greater, respectively, than perimeter trees in April. In contrast, leaf gs and Ci/Ca of median trees were and Ci/Ca of perimeter trees were
July 2005
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