184 Burger and Prager: Deep-Rooted Trees for Urban Environments Arboriculture & Urban Forestry 2008. 34(3):184–190. Deep-Rooted Trees for Urban Environments: Selection and Propagation David W. Burger and Todd E. Prager Abstract. Seedling liners of three tree species (Fraxinus uhdei, Pistacia chinensis, and Zelkova serrata) were planted in the field and grown for 18 months. Pneumatic air excavation followed by digital photography, three-dimensional modeling, and root analysis showed there were significant differences in root architecture among the three species and within each species’ population. Among the three species, Pistacia chinensis had, on average, the deepest, most vertically oriented root systems and Fraxinus uhdei and Zelkova serrata the shallowest; however, there were shallow-rooted and deep-rooted genotypes in each species. Shallow- rooted and deep-rooted genotypes of Fraxinus and Zelkova selected from the seedling populations were propagated vegetatively by cuttings, planted in the field, and grown for 5 to 6 years. On excavation and three-dimensional model creation, the root architecture of the cutting-propagated clones was assessed using liminal angles and individual root angles. Cutting-propagated clones of shallow-rooted parents were shallow-rooted; thus, they maintained the parents’ root architecture. Cutting-propagated clones of deep-rooted parents were also shallow-rooted; they did not maintain their parents’ root architecture. Results are discussed in terms of genetic, physiological (e.g., auxin treatment, adventitious root formation), and environmental (e.g., soil moisture) factors that can affect tree root growth and development. Key Words. Arboriculture; gravitropism; infrastructure damage; liminal angle; root architecture, root growth; root system genetics; street tree; urban forestry. Trees in urban environments provide many biologic, environ- mental, economic, and social benefits. These benefits come with some cost, however. Some trees have root systems that cause substantial damage to sidewalks, curbs, and gutters. Damage results from a number of factors: small planting areas, restrictive soils, and use of large-stature trees in confined areas (Costello and Jones 2003). In some cases, the trees’ inherent tendency to have shallow roots is thought to be a key factor (Hamilton 1984a). As these shallow roots produce secondary thickening, they tend to lift and crack pavements. Several tree species com- monly planted in northern California, U.S., have been associated with sidewalk and curb displacement: Liquidambar styraciflua (sweetgum), Morus alba (white mulberry), Fraxinus spp. (ash), Ulmus spp. (elm), Magnolia grandiflora (Southern magnolia), Prunus spp., Pinus radiata (Monterey pine), Eucalyptus globu- lus (blue gum eucalyptus), and Cinnamomum camphora (cam- phor) (Hamilton 1984a; Costello and Jones 2003). This problem is of major proportions in many cities. In a 1984 survey of cities in the Bay Area of California, 60% of the street trees were estimated to have caused some or severe damage to the urban infrastructure (Hamilton 1984a). A subsequent survey of sidewalks in San Jose, California, found the estimated repair cost for tree-related damage to be $14.3 million and annual concrete repair costs attributed to tree damage ranged from $0.18 to $13.65 per tree (Peper and McPherson 1995). Most recently, McPherson and Peper (2000) found in California that approxi- mately $70.7 million was spent annually statewide as a result of conflicts between tree roots and urban infrastructure (e.g., side- walks, street pavement, curbs, and gutters). It is quite apparent that even a partial solution to this problem would result in sub- stantial savings for city residents and governments. Various strategies such as engineering, design and improved materials, and biologic/genetic approaches have been suggested ©2008 International Society of Arboriculture in hopes of solving this problem (Hamilton 1984b; Costello and Jones 2003). Engineering solutions include the use of steel plates bolted directly to exposed roots to prevent or minimize future damage and the use of root barriers in an attempt to force roots down below sidewalks and curbs. Design solutions include pro- viding adequate planting strip space for tree trunk diameter in- creases and root crown flare. Newer paving materials may pro- vide the necessary flexibility to prevent cracking and complete disruption of the pavement. Another strategy is the biologic/ genetic approach: to identify, select, and vegetatively propagate trees that are genetically “programmed” to be deep-rooted. The basic premise behind this approach is that it is reasonable to expect as much variability in belowground architecture for trees as is found aboveground (Barker 1987; Bowman 1941). Two questions are addressed in this study: 1) are there genetic differ- ences in root depth and orientation between and within tree species; and 2) if root architecture is under genetic control, can it be maintained through vegetative propagation techniques? MATERIALS AND METHODS Survey A survey of six northern California cities (Modesto, Redwood City, Palo Alto, Berkeley, Sacramento, Sunnyvale) was con- ducted to identify species observed to cause infrastructure dam- age. More than 20 species were identified and three were se- lected for the research project: Fraxinus uhdei (Wenzig) Lin- gelsh. (green ash), Pistacia chinensis Bunge (Chinese pistache), and Zelkova serrata (Thunb.) Makino (zelkova). Seed-Propagated Trees in the Field Fifty seed-propagated individuals (liners) of each of the selected tree species were purchased and planted in a field plot in July
May 2008
| 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
