Arboriculture & Urban Forestry 39(6): November 2013 289 Table 4. Mean crown condition rating and associated biotic and abiotic problems for 11 common landscape tree genera assessed at 65 non-residential landscaped sites in the Phoenix metropolitan area. Non-residential survey assessment was during winter 2006–2007 (N = 707). Genera taxa Acacia Brachychiton Eucalyptus Fraxinus Olea Parkinsonia Pinus Prosopis Quercus Rhus Ulmus N 64 53 40 60 60 63 73 73 51 49 56 Crown rating 3.03z 2.42 2.35 2.55 2.35 2.79 2.49 3.04 2.16 2.39 3.35 z Crown rating: 1 = Poor; 2 = Fair; 3 = Good; and 4 = Very Good. lowest. Some biotic and abiotic problems were associated with certain genera. For example, slime flux was detected in Acacia Parkinsonia, and Prosopis trees. Sooty canker was most com- monly observed in Brachychiton and Ulmus trees. Aphids were only detected on Quercus and Fraxinus trees. Wood-pecking bird damage and pine blight were primary problems observed on Pinus trees. Sunscald injury of trunk and branch tissues was most commonly detected on Brachychiton, Olea, and Quercus trees. DISCUSSION Although crown condition was rated as very good or good for the majority of trees at both residential and non-residential sites, researchers found that residential trees in Phoenix had generally fewer visual health issues than trees in non-residential settings. Urban forests are a complex and diverse mixture of trees of many taxa and age classes. In these studies, researchers were able to differentiate grouping of trees by species com- position, but not by age class. As a result, authors were not able to assign age class as an independent variable to deter- mine if differences in canopy condition were related to tree age differences within each urban land-use type. The authors recognize the potential limitations of these health data due to differential mortality and dieback of older trees. In addi- tion, the above- and belowground environmental conditions within which urban trees grow can range from excellent to being severely constricted by the built environment, and it is possible that environmental constrictions in Phoenix to tree productivity are more severe at non-residential sites. Despite these limitations, the study authors believe that valuable insights were gained regarding overall trends of tree health related to broad measures of urban classification, such as urban land-use from the citywide survey data presented in this paper. When tree visual health was scrutinized in greater detail, a diverse set of abiotic and biotic stressors were detected at non- residential sites. Half of the trees had major physical wounds present on their trunks, main scaffold branches, or roots, where- as 70% had pruning problems. While researchers could not determine with certainty if pruning problems were caused by the removal of dead branches on older or diseased trees or associ- ated with the training of the crown architectures of young trees, researchers suspect that most pruning problems are associated with intensive crown management of young trees. The majority of development (by land area) in the Phoenix metropolitan area has occurred within that last 50 years, with a significant portion of that during the last 20 years (Larson et.al. 2005). There- fore, it is reasonable to surmise that pruning strategies for trees planted in landscaped areas of this large portion of the city are focused on live crown management and not the removal of dead branches associated mature trees with significant crown dieback. Biotic problems were detected in just over 40% of the trees at non-residential sites and biotic problems were detected in most trees with poor crown condition ratings. These biotic problems were often species-specific and included diseases of common land- scape trees in the Phoenix area, including ash decline in Fraxinus and Verticillium wilt in Olea, both of which can cause significant canopy dieback. Other biotic problems were specific abiotic con- ditions, including slime flux in desert-adapted Parkinsonia and Prosopis, which was associated with pruning wounds, and sooty canker in Brachychiton trees, which was associated with sunscald. It was found that the mortality rate for the trees that were moni- tored at non-residential sites for the five years averaged about 4.2% per annum. This mortality rate is similar to that previously reported by Nowak et al. (2004) for Baltimore, Maryland, U.S. In cities across the United States, a tree planting campaign is one strategy used to increase urban forest cover density and diversity and to mitigate atmospheric pollution, urban heating, and improve urban ecosystem function (Stone and Rodgers 2001; Kalnay and Cai 2003; Jenerette et al. 2007). For example, Phoenix’s tree and shade master plan provides a framework to achieve an average 25% tree canopy coverage by 2030 (City of Phoenix Tree and Shade Master Plan). In Phoenix, the combi- nation of heightened public awareness about landscape water conservation and advocacy of the use of low-water-use trees has resulted in the increased planting of trees in the family Fabaceae and in particular desert-native trees, such as those in the genera Parkinsonia and Prosopis, during the last 20 years. Desert-adapted and desert-native trees, such as Parkinsonia and Prosopis, usually have broadly spreading, complex crown structures that sometimes extend fully to the ground as a nor- mal morphological adaptation to an arid climate. In Phoenix, these trees are often planted into non-residential sites, such as parking medians and transportation corridors, with severe above- and belowground spatial limitations due to the den- sity of the built environment and/or because local ordinances stipulate that scaffold branches must originate from trunks no lower than a height of 3.6 m. Management strategies for trees in these difficult sites include extensive removal of live stems and branches through pruning practices, such as crown raising, thinning, and crown reduction. The authors ©2013 International Society of Arboriculture Biotic 38% 49% 35% 38% 30% 44% 34% 67% 70% 18% 25% Primary problem Slime flux Sooty canker Slime flux Ash decline Verticillium wilt Slime flux Bird damage Slime flux Aphids Wood rot Sooty canker Abiotic 3% 49% 25% 17% 40% 5% 53% 0% 31% 29% 2% Primary problem Sunscald Iron chlorosis Sunscald Sunscald Pine blight Sunscald Dieback
November 2013
| 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
