Arboriculture & Urban Forestry 39(6): November 2013 Sustainable urban forests in the southwestern United States should be designed, installed, and managed by people in ways that are able to improve human health, quality of life, and commerce without excessive consumption of natural resources (Martin 2008). A holistic knowledge of the impact of landscape design and management practices on overall urban forest function is essential to ensure urban tree health and longevity. In Phoenix, the authors have noted anecdotally that the intensity of urban tree care practices, such as crown raising and crown thinning, generally appear to be greater at commercial, industrial, and public sites as well as transporta- tion corridors, such as streetscapes and landscaped interstate highways, than at residential sites. These differences in man- agement intensity are probably caused by the greater like- lihood that landscape plantings within non-residential land- uses are managed more regularly by professional landscape maintenance companies than those within residential areas. In hot desert regions, excessive pruning of landscape trees might predispose some tree taxa to locally common abiotic stressors, such as trunk and crown sunscald injury, which can be linked to biotic stressors, such as wood decay and sooty canker. Assessments of tree health in urban landscapes are rare (Cumming et al. 2001). Monitoring urban forest health is es- sential to identifying changes within urban ecosystems as well as providing a foundation for improving resource management practices (McPherson 1993). In this paper, researchers present an overview of two long-term field studies on the health and role of trees in the Phoenix metropolitan area. While the term plant health is abstract and has no universal definition (Doring et al. 2012), the authors evaluated tree health in Phoenix using two commonly accepted indicators: crown condition and the absence of external symptoms and signs of disease causing agents, pests, and abiotic or stress problems (Kolb et al. 1994). METHODS The following is a description of the two long-term field studies that were used to present an overview of the health and mortal- ity of trees in the Phoenix metropolitan region. Both studies are a part of the Central Arizona Long-Term Ecological Research (CAP LTER) project that was initiated in 1998 to study eco- system dynamics across the Phoenix metropolitan region. Survey 200 This extensive survey is an integral part of the CAP LTER monitoring program and consists of 204 sites distributed across the Phoenix metropolitan basin and surrounding So- noran Desert, encompassing a total area of 6,400 km2 site has an area of approximately 900 m2. These 204 sites are . Each arrayed in a dual-density, randomized, tessellation-stratified design (Hope et al. 2003) to enable characterization of land- use patches in terms of key biotic, physical, and chemical variables, and to examine relationships between land-use, general plant diversity, native plant diversity, plant volume, soil nutrient status, and socioeconomic indices along an indirect urban gradient. Between February and April 2010, researchers surveyed all 204 sites for the presence of trees and segregated them taxonomically, using JMP 8.0 (SAS, Cary, North Carolina, U.S.). The study authors defined a tree as being a woody plant having one or more erect perennial 287 stem (trunk) with a cumulative diameter of at least 7.6 cm at a point 1.37 m above the ground, a formed crown of foliage, and a mature height of at least 3.0 m. Next, within a subset of sites classified as urban (N = 104 of 204), the overall crown condition of trees was visually evaluated and rated as either very good (4), good (3), fair (2), or poor (1) based on a matrix of condition factors used for plant appraisal (CTLA 1992). 2003–2007 Non-residential Tree Survey Records of tree mortality were made annually (2003–2007) dur- ing winter months at 50 irrigated sites with immediate public access (commercial, institutional, or transportation land-uses). The 50 sites were arrayed in a broad northwest to southeast tran- sect gradient across the region. Within this transect gradient, sites were distributed equally using the Burgess Urban Land Use Model of monoconcentric circles, expanding from the urban core to urban fringe into seven previously defined concentric zones (bandwidth of 6.5 km) of air temperature and atmospheric CO2 level (Stabler and Martin 2000). Each site averaged 930 m2 in area and contained approximately eight trees, 402 total estab- lished trees (36 unique taxa) at the 50 sites in 2003. In this pa- per, researchers present tree mortality rates from this population of trees over a five-year period. No data were collected on trees planted within sites after the start of the data collection period. During winter 2006–2007, data about tree crown condi- tion were collected at these 50 sites plus 15 additional non- residential locations selected from the CAP LTER 200 point survey sites (N = 707). For each tree, the overall condition was evaluated and rated as very good, good, fair, or poor, based on condition factors used for plant appraisal (CTLA 1992). Each tree was assessed for the absence or presence of known biotic concerns (diseases and pests) common to urban tress in Phoenix, including slime flux, ash decline, sooty canker, Verticillium wilt, wood rot, Phymatotrichopsis root rot, fire blight, true mistletoe, aphids, sapsucker bird damage, as well as for abiotic problems (stress and problems with un- known etiology) common in urban trees in Phoenix, includ- ing sunscald, pine blight, chlorosis, and leaf margin necrosis (Streets 1969; Olsen 2001; Bricker and Stutz 2004). Physical and mechanical damage to roots, trunks, or branches of each tree was assessed using the protocol of Cummings et al. (2001), and the location, types, and severity of damage was recorded. For both studies, all sites were classified according to the Maricopa Association of Governments (MAG) land- use classification system. Sites included a variety of des- ert and residential and non-residential urban land-use types, including industrial, institutional, transportation (streetscapes) and golf courses parks, and urban waterways. RESULTS Survey 200 Across the whole study area, 165 of the 204 sites were located within the Phoenix metropolitan area. The remaining 39 sites were external to the city within the surrounding Sonoran Desert. Across the whole study area, 641 trees were found distributed across 130 of the 204 sites, with 401 trees occurring at 104 of the 165 sites within the metropolitan area. In Table 1, research- ers show the taxonomic distribution of these 401 trees within ©2013 International Society of Arboriculture
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
