Journal of Arboriculture 31(1): January 2005 31 a specific situation. Ultimately, the decision on how to compromise, or not, and best manage any one section of a ROW lies in the hands of the professional vegetation manager. An important aspect of communication with stakehold- ers revolves around the concept of “tolerance levels” (see Stern et al. 1959). Tolerance levels are specific descriptions of vegetation condition—individual plant and plant commu- nity size, abundance, and composition—that, if exceeded, trigger a need to intervene. Inventory and monitoring are a part of IVM (see Steps 5 and 6). Pests are not treated unless they exceed the critical threshold. Well-defined thresholds are an important element of IVM (McLoughlin 1997, 2002) that can be useful in communicating management needs to various stakeholders; for example, thresholds and tolerance levels can be used to demonstrate the cyclic nature of vegetation dynamics, which supports a need to control vegetation on a regular basis. Step 3: Compiling Treatment Options Singular use of any one treatment method across all sites and conditions is not an IVM approach. ROW vegetation managers can conduct IVM only if multiple treatment options are available for application to any one site and in any one setting. Different treatment options may be needed to match variable environmental and site conditions on a ROW (see Step 5) or to address other stakeholder concerns and interests (see Step 2). Vegetation treatments can be grouped into categories, such as mechanical, chemical, cultural, physical, biological, and ecological (McLoughlin 1997, 2002). It is most common to use two or more of these categories of treatment on any one site at any one time (e.g., the cut-stump method of killing trees combines mechanical and chemical treatments and leads to the biological/ecological control associated with removing individual trees on ROWs, as explained at the beginning of this paper). IVM does focus on integrating biological/ecological control into all treatment schemes. Such control prevents the buildup of pest populations, which is a critical element of the integrated control concept (Stern et al. 1959) and IPM (McLoughlin 1997, 2002). A primary objective of vegetation management in an IVM system on powerline corridors should be to create stable, low-growing plant communities, which leads to a reduction in pest (tree) populations (Niering and Goodwin 1974). This biological/ecological control produces a long-term reduc- tion in treatment efforts and a reduction in herbicide use (Nowak and Abrahamson 1993; Finch and Shupe 1997). Step 4: Accounting for Economic and Environmental Effects of Treatments Choice of treatment must be made with an understanding of potential socioeconomic and environmental impacts. Approaches to this can be unique to each person and company. A useful metric is cost effectiveness (see Nowak et al. [1992] and Abrahamson et al. [1995] for details on use and application, based on research and development studies). Cost effectiveness is a measure of the success of a treatment in terms of economics, plant community dynam- ics, and related environmental considerations. It can be defined by its two component parts: cost and effectiveness. Cost for ROW vegetation management can be viewed as including direct costs and indirect costs. Direct costs pertain to the actual outlay of money made to treat ROW vegeta- tion. Labor, equipment, and materials are commonly reported as direct costs. Indirect costs are the loss or nonproduction of values or service that can result from a treatment. These are often associated with water quality, wildlife habitat, and aesthetics, or other ways that the environment can be degraded. They are sometimes referred to as “environmental externalities,” though environmental externalities can be either positive or negative, depending on whether they are a benefit or a cost. Other indirect costs are associated with risk of treatment to human health, and related pollution of soil, air, and sound (noise). Actual dollar amounts are difficult to ascribe to indirect costs. Effectiveness pertains to production of desired vegetation conditions and associated benefits and values, including safe and reliable transmission of electricity, promotion of diverse plant and animal communities, protection of riparian areas and water quality, creation of visual attributes fashioned to minimize negative impacts to aesthetic appeal or quality, and enhancement of opportunities for recreational endeavors. Time frames for consideration of cost effectiveness can be short- or long-term. Because vegetation management and the IVM process is a long-term affair, efforts must be made to balance short-term savings with long-term costs. For example, it may be less costly, monetarily, to mow a ROW today than use herbicides. Mowing may produce higher costs over the long-term because of short-term control of vegetation conditions and shorter treatment cycles than can be achieved with other treatments (e.g., see Johnstone 1990; Nowak et al. 1995). Vegetation managers need to select the most cost- effective treatment for each ROW management scenario. Because no two situations are alike, different treatments are often needed to maximize cost effectiveness (see Step 5). In general, we expect that treatments will lead to a reduction in the pest organism (trees) and will minimize (prevent) further development of a problem, which will lead to a reduction in management inputs and a reduction in both direct and indirect costs. IVM equates to using treatments that are least costly in terms of dollars, produce minimal risks for human health and the environment, and create the desired vegeta- tion conditions and associated positive values or externali- ties associated with these conditions over the long-term. ©2005 International Society of Arboriculture
January 2005
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