Arboriculture & Urban Forestry 36(5): September 2010 Arboriculture & Urban Forestry 2010. 36(5): 193–205 193 Tree Root Ecology in the Urban Environment and Implications for a Sustainable Rhizosphere Susan D. Day, P. Eric Wiseman, Sarah B. Dickinson, and J. Roger Harris Abstract. This review examines current understandings of how the belowground characteristics of urban settings affect tree roots as well as how tree roots contribute to biogeochemical processes in this belowground environment. Soil characteristics common to the urban environment in- clude soil compaction and other physical impediments to root exploration, elevated pH, altered temperature and moisture patterns, and the pres- ence of contaminants. These conditions may alter the growth dynamics, morphology, and physiology of roots. At the same time, roots have a profound effect on the soil environment, with trees directing 40%–73% of assimilated carbon below ground. Urban rhizosphere ecology is a top- ic of renewed interest for research not only because of its critical role in the urban ecosystem, but also because of its role in global environmen- tal issues. In addition to its obvious contribution to aboveground growth, root exploration of the soil environment can influence environmen- tal sustainability through root contributions to soil structure and drainage. Root influence is further mediated by the intimate role of roots in soil biological activity and thus carbon storage and nutrient cycling. Current advances and implications for emerging research are discussed. Key Words. Heavy Metals; Road Salt; Root Periodicity; Soil Compaction; Soil Structure; Urban Hydrology; Urban Infrastructure. The root-soil environment—the urban rhizosphere—is critical not only to tree health, but to urban ecosystem function as well. The performance of urban trees depends upon the ability of their root systems to acquire resources and provide anchorage. How- ever, conditions prevalent in the built environment, such as com- pacted soils, underground infrastructure, chemical contamination, and excessive heat, create a unique and often unaccommodating environment that may impair root growth and development. In addition, practices associated with establishing and maintaining a landscape, such as transplanting large trees and employing ir- rigation systems, can alter tree root growth dynamics. In turn, tree roots alter the belowground environment through their influence on biological, physical, and chemical soil properties. This urban rhizosphere ecology has implications for both establishing trees in cities, and for assessing potential ecosystem services that trees, and their root systems in particular, provide to society. The scope of this review includes root responses to environmental elements typical of urban settings (for example, soil compaction) and root interactions with that environment through carbon deposition and other means. This paper avoids discussion of root architecture and specific root management practices (e.g., directing roots with barriers or planting space designs, root pruning, fertiliza- tion), and instead focuses on root ecological interactions with the environment. These interactions include growth periodicity; root response to physical constraints and soil chemical and biological properties; and root contributions to characteristics of the below- ground environment that relate to contemporary discussions of environmental sustainability, such as carbon sequestration, ero- sion control, and soil hydrological processes. The purpose of this paper is to provide a review of the literature in this emerging area of inquiry in the context of arboriculture and urban forestry that will help identify knowledge gaps and inform future research. ROOT GROWTH PERIODICITY—RESPONSES TO TRANSPLANTING, SOIL TEMPERATURE, AND SEASON Root growth, especially fine root production and mortality, is a dominant feature of the belowground ecosystem where trees are present. In arboriculture and urban forestry, the ques- tion “When do tree roots grow?” has been largely addressed in the context of transplanting (Harris et al. 2001; Harris et al. 2002; Richardson-Calfee et al. 2007; Richardson-Calfee et al. 2008), where tree establishment depends upon root explora- tion of the new site (Harris 2007) and can be influenced con- siderably by transplant time (Richardson-Calfee et al. 2004). Mathematical modeling of root growth periodicity has shown that resource limitation feedback between shoot and root growth results in a balance between the two processes that is favorable to tree growth in the particular environment where it is located (Thornley 1972; Thaler and Pagés 1998). Investigators have re- ported that many temperate woody plants exhibit pronounced pe- riods of root elongation in autumn and spring, although activity level will decline during shoot expansion as resources are allo- cated to aboveground parts (Stone and Schubert 1959; Stone et al. 1962; Cripps 1970 Roberts 1976; Deans 1979; Dell and Wal- lace 1983; Wargo 1983; Deans and Ford 1986; Harris et al. 1995; Harris and Fanelli 1999). Although root growth is clearly linked to shoot growth by endogenous signals (Richardson 1958; Lar- son and Whitmore 1970; Farmer 1975), climate, local weather, and soil conditions are key factors controlling these root growth periods. In particular, root growth is strongly influenced by soil temperature and moisture (Lyr and Hoffman 1967). Each species has a different amplitude, or “ideal” range, of soil temperature that is suitable for root growth. This range usually corresponds to the climate of the region where the species (or species ecotype) is native. The typical temperature range that permits root growth ©2010 International Society of Arboriculture
September 2010
| 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
