Tree Appraisal: The Four Primary Factors By Scott Cullen, RCA #348
Introduction This article is about four traditional primary appraisal factors (Size, Species, Condition, and Location), which have always had two roles. It builds on two earlier articles (Cullen and McNeil 2015, Cullen 2022). The Guide for Plant Appraisal, 10th Edition1 (CTLA 2020) notes that “...depreciation is the combination three factors” (p. 61), and that “previous editions of the Guide described three depreciation factors: species, condition, and location... [while] this edition presents three categories of depreciation: physical deterioration (condition), functional limitations, and external limitations...” (p. 62). Purcell (2019, 2020) similarly described depreciation factors in the 10th Edition. This article also refers to earlier editions of the Guide. 9th
(CTLA 2000)
6th
(Neely 1983)
3rd
(Lewis 1970)
8th
(CTLA 1992)
5th
(Neely 1979)
2nd
(Tilford 1965)
7th
(Neely 1988)
4th
(Neely 1975)
1st
(NSTC/NAA 1957)
In fact, the 4th through 9th Editions of the Guide described four—not just three—primary appraisal factors: Size, Species, Condition, and Location. The Manual for Plant Appraisers (CTLA 1986) described the same four “factors in the determination of value” (p. 16). Purpose One of the main purposes of this article is to explain that those four primary appraisal factors always had two roles: physical, observable, factual tree or plant attributes; and depreciation ratings. This article also explains that the 10th Edition retains the four physical observable attributes, even though the depreciation category labels have changed. This article is about the four factors generally, it is not about depreciation. An additional purpose of this article is adding to the secondary literature that may inform development of the 11th Edition2.
The 10th Edition was released in August 2018 (CTLA 2018a, dark green cover). Within months, the first printing was withdrawn to correct formatting, typography, and other errors (CTLA 2018b). A second printing, released in July 2019 (CTLA 2019, light green cover), still contained errors and significant conceptual flaws. In November 2019, some of the 10th Edition worksheets were revealed to be unworkable (Cullen 2019). Revised worksheets (ISA 2020a, 2020b) attempted to correct errors and are included in the 10th Edition Revised (CTLA 2020, light green cover). The Quebec Chapter of the International Society of Arboriculture released a French translation and adaptation, of the 2020 Revised Edition, for the Canadian province of Quebec (SIAQ 2023, advertised with blue cover).
1
References in this article are to the 10th Edition Revised (2020); however, pagination is generally consistent in the three printings. Anecdotally, in 2025 some tree appraisers continue to use the 9th Edition (CTLA 2000). The 4th–10th Editions of the Guide were published by the International Society of Arboriculture—ISA. The 5th–10th Editions were authored by the Council of Tree and Landscape Appraisers— CTLA. In December 2023 ISA, with support from the other CTLA organizations, announced that public comments on the 10th Edition would be accepted throughout 2024, followed by a five year drafting and review process leading to publication of the 11th Edition by 2030 (ISA 2024a, ISA 2024b, Vidich 2024). In May 2025 ISA announced a) the appointment of 13 CTLA comment and content reviewers, and b) an updated schedule (ISA 2025). 2
American Society of Consulting Arborists®
10
Arboricultural Consultant volume 58 issue 3 2025