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)
8th (CTLA 1992)
7th (Neely 1988)
6th (Neely 1983)
5th (Neely 1979)
4th (Neely 1975)
3rd (Lewis 1970)
2nd (Tilford 1965)
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 .
1The 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 Within months, the first printing was withdrawn to correct formatting, typography, and other errors (CTLA 2018b).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).
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).
2The 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).
Tree Appraisal: The Four Primary Factors continued
What Are Factors?
The 10th Edition does not define the term factor, even though a word search (n=3) finds it used 24 times. The Dictionary of Real Estate Appraisal (Appraisal Institute 2022) defines factor as “1. One of the elements that contributes to a given result.” Merriam-Webster (2025) defines factor as “one [ingredient] that actively contributes to the production of a result.”
As defined, factors are broadly any elements that contribute to an appraisal result, including both a) facts and b) appraiser judgments (e.g., adjustments, assessments, ratings, weightings).
What are results? The 10th Edition describes assignment result as the end product of the appraisal process, “the appraiser’s opinions and conclusions developed for a specific assignment” (p. 7).
Historical Perspective
As explained in the Introduction to this article, earlier editions of the Guide described four primary appraisal factors: Size, Species, Condition, and Location3. This section puts these factors in historical perspective.
As shown in Figure 1, the Guide emphasized the importance of these four factors. The 7th, 8th, and 9th Editions stressed them with a dedicated chapter or section. The 9th Edition stated “...these factors are essential considerations when appraising the value of a plant...” (p. 25).
Guide Dedicated
Edition * Chapter Page Descriptive Emphasis
Fourth 3 four basic factors
Fifth 10 four major factors
Sixth 18 four major factors
Seventh Chapter 3 10 four primary factors
Eighth Section II 13 four primary factors
Ninth Chapter 4 25 four primary factors
* The International Society of Arboriculture ISA recently made the Ninth Edition available digitally through its online store. With ISA permission Russ Carlson, RCA# 354, recently made the First through Eighth Editions available digitally to ASCA members through the ASCA Exchange.
Figure 1. Four appraisal factors emphasized in earlier Guide editions.
Cullen and McNeil (2015)—in a 9th Edition context—explained that the Size, Species, Condition, and Location factors were physical, observable tree or plant attributes considered in all appraisals; and were distinct from the factor ratings applied to Species, Condition, and Location for depreciation in the cost approach. Cullen (2022)—in a 10th Edition context—similarly explained that the four primary factors always had two roles: physical, observable tree or plant attributes, and depreciation ratings; and that the 10th Edition retains the four physical, observable attributes, but replaces Species, Condition, and Location depreciation rating categories with Physical4, Functional Limitations, and External Limitations.
3The 1st, 2nd, and 3rd Editions also described three basic factors to be considered in determining the monetary value of shade and ornamental trees: size, kind (species), and condition. The 4th Edition added location.
4The 10th Ed. adopts the depreciation categories used in “general appraisal practice” (p. 61), but uses the new Physical Deterioration label interchangeably with the traditional Condition label (p. 62).
Tree Appraisal: The Four Primary Factors continued
“…the four primary factors always had two roles: physical, observable tree or plant attributes, and depreciation ratings…”
Approaches to Value
The approaches are important in understanding this historical perspective. An appraisal approach is simply defined as a systematic process for developing an opinion of appraised value or assignment result (Appraisal Institute 2022). The three appraisal approaches rely on different types of data as shown in Figure 2.
Appraisal Approach
Cost
Sales Comparison (Market in 9th Ed.)
Income
Type of Data
Reproduction, Functional Replacement † , or Repair Costs
Sales Prices
Income and Expenses
† Reproduction and Functional Replacement costs are distinguished in the 10th Edition (p. 55 ).
Figure 2. Approaches to value rely on different types of data.
Stone’s (1916) foundational tree appraisal method used what we now understand to be a cost approach. He used the cost of available size nursery trees to develop a cost per sq. in. of trunk cross-sectional area which could be used to estimate the cost of a larger appraised tree. The Felt Formula (e.g. Felt 1929), Felt-Spicer Formula (e.g. Spicer 1953)5, and the 1st through 8th Editions of the Guide all similarly used what we now understand to be a cost approach. The 5th through 8th Editions briefly alluded to income appraisal of orchard crops and market value of timber, but did not describe different approaches to value.
The 9th Edition (p. 20) first recognized three distinct “approaches to value” in tree appraisal: Cost, Income, and Market. The 10th Edition (p. 25) reinforces and expands on the role of the three approaches to value or assignment result: Cost, Income, and Sales Comparison (Market in the 9th).
The Two Roles of the Four Primary Factors
Physical, observable plant attributes. The four primary appraisal factors described in earlier Guide editions (Size, Species, Condition, and Location) are physical attributes or characteristics of appraised trees or other plants. They are observable and factual. They are objective. Tate (1989) succinctly described these “objective variables:”
“There is only one correct tree circumference at 4.5 feet for each tree... The determination of tree species is a precise observation... it is a sugar maple or it is not... The tree is growing in a mall or it is not. It is growing on a street curbside extension or it’s growing in a front yard... the tree has insects or disease or it does not... does or does not have a trunk cavity... a split crotch and so on.”
These four primary appraisal factors were always a consideration in developing an opinion of value. Recall that the 9th Edition described them as essential. The factual and objective attributes and characteristics of the appraised plants accurately observed by the appraiser at the start of the appraisal would not ordinarily change over the course of that appraisal, regardless of the appraisal approach, the method, or the type of data used by the method; and regardless of factor ratings subsequently applied.
5For a more complete history see Cullen and McNeil (2020, Appendix IV).
Tree Appraisal: The Four Primary Factors continued
Factor ratings (depreciation). Stone’s (1916) foundational method adjusted for Species, Condition, and Location to reflect value. From the 4th Edition through the 9th Edition, cost estimates could be adjusted downward for Species, Condition, and Location6 . Based on the physical, observable, and factual Species, Condition, and Location factors, the appraiser could develop factor ratings from 0%–100% (e.g., 8th Ed. p. 34, 9th Ed. pp. 15, 25). The ratings were “relative to a high-quality specimen” (8th Ed. p. 13, 9th Ed. p. 25). The 9th Edition first recognized these adjustments as appraisal depreciation, in the cost approach (p. 21).
In contrast to the observable and factual plant attributes, Tate (1989) described these ratings as “subjective variables.” The 8th Edition (p. 13) and 9th Edition (p. 25) also described the factor ratings as subjective.
The Factors and Their Ratings Are Distinct
The Species, Condition, and Location factors are factual observations. They are data. The appraiser’s percentage ratings of those factors are conclusions. They are not the same thing. Tree and plant appraisers should understand that their factual observations and their conclusions or opinions about those observations are distinct.
The 10th Edition
The preceding Historical Perspective section describes the Guide’s traditional emphasis of four primary appraisal factors (Size, Species, Condition, and Location) which always had two roles.
10th Edition Physical, Observable Plant Attributes
The 10th Edition uses factor to describe an assortment of appraisal variables. As noted above, a word search (n=3) finds it used 24 times (in its broadest sense, as defined in the Introduction to this article). Cullen (2022) explained, however, that the 10th Edition retains the traditional four primary appraisal factors as physical, observable plant attributes in Chapter 4 – Data Collection, and in the Appraisal Field Data Sheet (p.155).7 See Figure 3. The 10th Edition describes these as quantitative data (p.31).
!"#A%CD"(A *D+DF,-((A.+/-0
7(D0+F1++%/"8+A ,SDO+A% 7D9A
!"#A
!)AT"A8
C5P;"*"5P
>(S(?A
c5T(*"5P
ed(TASAP*
1OO%D/#D(FP/A(4 *D+DF5SAA+
CD()*A+%I -I IL 011 2+AA%"P45+S(*"5P
CD()*A+%I -I 011 2+AA%9P45+S(*"5P :))AP;"<%0 0-1
CD()*A+%I I- I= 011 2+AA%9P45+S(*"5P
CD()*A+%I 1@ 10 01A >(S(?A%B%9PCa+E
CD()*A+%I -L 011 Cd"AP*%"P45+S(*"5P
CD()*A+%I IL% 011 01A ed(TASAP*
P/98%AF:;FF7S<#/.D(F!"#A%CD"(AF7(D0+F1++%/"8+A#F/0F+SAF !"#$ &'E#E)*;
10th Edition Depreciation
As explained in the Introduction to this article, the 10th Edition “presents three categories of depreciation: physical deterioration (condition), functional limitations, and external limitations” (p. 62). These replaced the Species, Condition, and Location depreciation factors used in earlier editions. As in earlier editions, in the 10th Edition appraisers can develop depreciation ratings from 0%–100% to be applied to basic cost estimates (p. 64). Detailed treatment of 10th Edition depreciation is beyond the scope of this article.8
6The 1st, 2nd, and 3rd Editions considered kind (species), and condition; the 4th Edition added location.
7The appraiser can also record depreciation rating percentages in the 10th Edition Appraisal Field Data Sheet, but this remains a separate role.
8For simplicity, this article treats size only as an observable physical attribute. Discussion of size as an effective depreciation variable in the 10th Edition, Functional Replacement Method—or earlier Cost of Cure—is beyond the scope of this article.
Tree Appraisal: The Four Primary Factors continued
Summary
This article explains that the 4th through 9th Editions of the Guide described and emphasized four primary appraisal factors: Size, Species, Condition, and Location. Those four primary appraisal factors always had two roles: physical, observable tree or plant attributes (facts, objective variables); and depreciation ratings from 0%–100% (conclusions, subjective variables). Observations and conclusions are not the same thing; they are distinct.
The 10th Edition retains the four physical, observable, factual plant attributes (Size, Species, Condition. and Location); but replaces the three traditional categories of depreciation with Physical Deterioration (Condition), Functional Limitations, and External Limitations. In the 10th Edition, the four physical, observable, factual plant attributes are still essential considerations in every appraisal, even though the cost approach depreciation category labels have changed.
One purpose of this article is adding to the secondary literature that may inform development of the 11th Edition. The 10th Edition lost the traditional emphasis of Size, Species, Condition. and Location as four primary appraisal factors. The 11th Edition developers may consider whether that is merely historical curiosity; or whether restoring the traditional emphasis of four primary appraisal factors would add clarity to the 11th Edition and to appraisal education.
Literature Cited Appraisal Institute. 2022. The Dictionary of Real Estate Appraisal, 7th Ed. Appraisal Institute, Chicago. 394pp.
CTLA (Council of Tree and Landscape Appraisers). 1986. Manual for Plant Appraisers (Supplement to 6th Ed.). CTLA, Washington, DC. 57pp.
CTLA (Council of Tree and Landscape Appraisers). 1992. Guide for Plant Appraisal, 8th Ed. International Society of Arboriculture, Savoy, IL. 103pp.
CTLA (Council of Tree and Landscape Appraisers). 2000. Guide for Plant Appraisal, 9th Ed. International Society of Arboriculture, Champaign, IL. 143pp.
CTLA (Council of Tree & Landscape Appraisers). 2018a. Guide for Plant Appraisal, 10th Edition [first printing]. International Society of Arboriculture, Champaign, IL. 170 pp.
CTLA (Council of Tree & Landscape Appraisers). 2018b. Guide for Plant Appraisal, 10th Edition. Corrigendum, Nov. 27, 2018, International Society of Arboriculture, Champaign, IL.
CTLA (Council of Tree and Landscape Appraisers). 2019. Guide for Plant Appraisal, 10th Ed. (second printing). International Society of Arboriculture, Atlanta, GA. 181pp.
CTLA (Council of Tree & Landscape Appraisers). 2020. Guide for Plant Appraisal, 10th Edition Revised [third printing]. International Society of Arboriculture, Atlanta, GA. 181 pp. Cullen, Scott. 2019. 10th Edition worksheets that don't work. ASCA Exchange Post, Nov. 6, 2019. http://exchange. asca-consultants.org/viewdocument/10th-edition-worksheets-that-dont?CommunityKey=e64f95bf-940f-4ed2-be6f3abbca2b7c10&tab=librarydocuments (accessed September 28, 2023)
Cullen, Scott. 2022. Tree appraisal: Location legacy in the 10th Edition. Arboricultural Consultant 55(1):17-22. Cullen, Scott and Joseph D. McNeil. 2015. Tree appraisal: Would it be missed? Arboricultural Consultant 48(3):3-7. Cullen, Scott and Joe McNeil. 2020. Tree appraisal: Installed unit costs. Arboricultural Consultant 53(3):4-11. Felt, E.P. 1929. Tree appraisal formula. The Shade Tree (1948 reprint 21(12)).
ISA. 2020a. Guide for Plant Appraisal, 10th Edition: Revised Corrigenda. https://wwv.isa-arbor.com/store/productfiles/Gui deforPlantAppraisal10thEditionRevised-2178-GPA_Corrigenda.pdf (accessed Dec. 27, 2020)
ISA. 2020b. Guide for Plant Appraisal, 10th Edition: Revised Forms. ISA Today, Nov. 17, 2020.
ISA. 2024a. Council of Tree and Landscape Appraisers Outlines Path for New Edition of Guide for Plant Appraisal. https:// www.isa-arbor.com/Newsroom/council-of-tree-and-landscape-appraisers-outlines-path-for-new-edition-of-guide-forplant-appraisa l (accessed March 11, 2024)
ISA. 2024b. Public review of the Guide for Plant Appraisal, 10th Edition. Arboricultural Consultant 57(1):11.
ISA. 2025. ISA Today May. Guide for Plant Appraisal Update. https://www.isa-arbor.com/Publications/ISA-Today/Issue/ Article/category/may-2025/guide-for-plant-appraisal-update
Lewis, Clarence E. (Ed.). 1970 Shade Tree Evaluation, Revision II [3rd Edition]. International Shade Tree Conference, Urbana, IL. 44 pp.
Merriam-Webster. 2025. https://www.merriam-webster.com/dictionary/factor
NSTC/NAA (National Shade Tree Conference/National Arborist Association). 1957. Shade Tree Evaluation [1st Edition]. National Shade Tree Conference, Columbus, OH, and National Arborist Association, Wooster, OH. Published at Wooster, OH. 14 pp.
Neely, Dan (Ed.). 1975. A Guide to the Professional Evaluation of Landscape Trees, Specimen Shrubs, and Evergreens, Revision III [4th Edition]. International Society of Arboriculture, Champaign, IL. 18 pp.
Neely, Dan (Ed.). 1979. Guide for Establishing Values of Trees and Other Plants, Revision IV [5th Edition]. International Society of Arboriculture, Champaign, IL. 42pp.
Neely, Dan (Ed.). 1983. Guide for Establishing Values of Trees and Other Plants, 6th Edition [Revision V]. International Society of Arboriculture, Champaign, IL. 48 pp.
Neely, Dan (Ed.). 1988. Valuation of Landscape Trees, Shrubs, and Other Plants. A Guide to the Methods and Procedures for Appraising Amenity Plants. , 7th Edition. International Society of Arboriculture, Urbana, IL. 50pp.
Purcell, Lindsey. 2019. Tree Appraisal and the Value of Trees [10th Edition]. Purdue Extension FNR-573-W. 7pp.
Purcell, Lindsey. 2020. An introduction to tree appraisal. Tree Care Industry XXXI(11):82-85 (November).
SIAQ (La Société internationale d'arboriculture Québec inc.). 2023. Guide pour l'évaluation monétaire des végétaux 2023. Traduction en français et adaptation de 10e édition américaine 2020. SIAQ, Laval, QC, Canada.
Spicer Orville W. 1953. Tree values and income tax deductions. Trees Magazine 13(5):8-9.
Stone, George E. 1916. Valuation of shade trees, pp. 255–258. In Shade Trees: Characteristics, Adaptation, Diseases and Care. Bulletin No. 170, Massachusetts Agricultural Experiment Station, Amherst, MA.
Tate, Robert. 1989. ISA tree valuation guide: A critical examination. Journal of Arboriculture 15(6):145-149.
Tilford, Paul E. (Ed.). 1965. Shade Tree Evaluation, Revision I [2nd Edition]. International Shade Tree Conference, Columbus, OH. 29 pp.
Vidich, Jamie. 2024. Council of Tree and Landscape Appraisers outlines path for revision of Guide for Plant Appraisal (press release). Arboricultural Consultant 57(1):10.
Backmatter
Acknowledgments: Thanks to Joe McNeil, RCA# 299—co-author of the cited earlier articles—for his insightful review of a draft of this article.
Scott Cullen, RCA #348, has been involved in various aspects of arboriculture since 1971. He is a full-time consultant in the tri-state metropolitan New York area. He is an ISA Certified Arborist, a CT Licensed Arborist, a NJ Licensed Tree Expert, a RI Licensed Arborist, and also holds the TRAQ credential. Scott is a CT Licensed Real Estate Broker, and earned a master’s degree in real estate development and investment from New York University. He was a member of ISA’s Plant Appraisal and Valuation Committee from its founding circa 2004 through its sunset in 2024, and was ISA’s representative to CTLA from 2011–2014.
