Journal of Arboriculture 31(4): July 2005 159 Table 2. Chronology of industry consensus guidance on tree and plant appraisal. Title Shade Tree Evaluation Shade Tree Evaluation, Revision I Shade Tree Evaluation, Revision II Guide to the Professional Evaluation of Landscape Trees, Specimen Shrubs and Evergreens, Revision III Guide for Establishing Values of Trees and Other Plants, Revision IV Guide for Establishing Values of Trees and Other Plants (6th ed.) Valuation of Landscape Trees, Shrubs, and Other Plants: A Guide to the Methods and Procedures for Appraising Amenity Plants (7th ed.) Guide for Plant Appraisal (8th ed.) Guide for Plant Appraisal (9th ed.) Author/year (NSTC/NAA 1957) (Tilford 1965) (Lewis 1970) (Neely 1975) (Neely 1979) (Neely 1983) (Neely 1988) (CTLA 1992) (CTLA 2000a) Table 3. Chronology of supplemental industry guidance on tree and plant appraisal.z Title Manual for Plant Appraisers (1st ed.)y Workbook—Guide for Plant Appraisal (8th ed.) Field Report Guide for Trunk Formula (8th ed.) Field Report Guide for Cost of Cure (8th ed.) Field Report Guide for Trunk Formula and Replacement Cost Methods (9th ed.) Workbook—Guide for Plant Appraisal (9th ed.) Author/year (CTLA 1986) (CTLA 1993) (CTLA 1995) (CTLA 1997) (CTLA 2000b) (CTLA 2000c) zTable 3 is limited to industry-wide or national, supplemental guidance. Regional supplemental guidance is beyond the scope of this paper. y Note that the 1986 manual was intended as a companion handbook and was not an edition or revision of the consensus guidance listed in Table 2. This additional material was incorporated into a single publication from the 1992 8th edition onward (CTLA 1992, p. vi). organizations, or by broader consensus. Guidance may gain authority by force of law or agreement or by general acceptance. Even with such authority, guidance may allow more discretion or latitude than standards. Standards Standards are statements of requirements for behavior or performance or for design. They may also include methods and additional guidance. Standards are seldom if ever developed by individuals. They may be developed by single organizations (e.g., ASCA 1996; RICS 2003) or government (NIST 2005) but more often by broader consensus. “Con- sensus bodies” include representatives from “materi- ally affected and interested parties” (ANSI 2005) or “stakeholders” (CEN 2005; ISO 2005; Standards Council of Canada 2005) including businesses, industry, trade, government, academia, the scientific community, consumers (BSI 2005; DIN 2005), or “others with relevant knowledge” (ISO 2005). Readers may be most familiar with national, consensus perfor- mance standards for tree care (e.g., BSI 1989; ANSI 1994; Standards Australia 1996; ANSI 2001) or related fields (e.g., ANSI 2004). Standards are often stated as binding but may be limited to guidance (e.g., Standards Australia 1999). Barrell (1995), as another example, notes that the British Standard 5837 (BSI 1991) “is more of a guidance reference than an absolute set of rules.” Standards gain their actual authority by force of law or agreement, by voluntary compliance, or by general acceptance. When guidance, advice, or clarification are included in standards, they may be as binding as the standards themselves (e.g., Ap- praisal Standards Board 2005, Statements; IVSC 2005, Guidance Notes) or may be supplemental (e.g., Appraisal Institute of Canada 2005, Practice Notes; Appraisal Standards Board 2005, Advisory Opinions). Even when not strictly binding (e.g., RICS 2003, Guidance Notes), supplemental guidance may be considered to be “best practice” or to define a “standard of care.” DISCUSSION As already noted, North American industry consensus guidance on tree and plant appraisal has not been promulgated as standard. Particular laws, regulations, or agreements may, however, require its use. Other- wise, other local or national methods may properly be used (ASCA 1996, §4.1(C)). Increasing international awareness, for example, may lead North American plant appraisers to other useful methods such as those described by Watson (2002). When consensus guidance is used, however, it is usually appropriate to rely on the most current version. There are situations when it is not strictly necessary to use the most current methods or guidance. In retrospective cases, for example, it is often appropriate to use the meth- ods or guidance that would have been current at some earlier date. Appraisers may intentionally use older meth- ods, techniques, or guidance, in whole or in part, if more suitable for a particular appraisal problem. There may be transition periods when either the most current version or its immediate predecessor is appropriate. Exceptions or departures from the most current methods or guidance generally should be disclosed in any appraisal report. ©2005 International Society of Arboriculture
July 2005
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