Abstract
A program is presented that computes tree valuation by the basic formula method. This program is designed to support portable, hand held, battery operated programmable calculators which are suitable for use in the field. Use of this program eliminates computational error that can jeopardize the validity and practical usefuleness of tree valuation by the basic formula method.
Accurate determination of the monetary value of trees is an important yet complex facet of practical arboriculture. Formal procedures have been published to determine tree value using the replacement method and the basic formula method (2, 3). A recent critique (4) illustrated some of the strengths of the procedures and made valuable suggestions for improvement, including some that could require major reorientation of the methodology of valuation by the basic formula method. An additional area where improvements could be made, but that would not require any significant restructuring of procedures, would be to increase the accuracy and precision of the computational aspects of tree valuation.
We have noted occasional serious errors in tree valuations by the basic formula method performed by our undergraduate students in the course Landscape Practices and Arboriculture (ORH 4235). Students are required to perform tree valuations as part of the laboratory component of this course. Valuations are evaluated by comparing those made by different students on the same trees and by comparing the student valuations with those made by a Certified Landscape Appraiser. As Tate (4) points out, some aspects of tree valuation are more subjective than others, and a great deal of the variation we have observed in valuation is attributable to disagreement over subjective aspects, such as the location factor. An additional, and sometimes very serious, source of error is in the computation itself. In some cases valuations were distorted more by computational errors than by disagreement over subjective factors. To help minimize computational error in tree valuation by the basic formula method, we have developed a program for use on an inexpensive (retail cost less than $50), hand held, battery operated electronic programmable calculator. It can be used in the field and will enable the arborist to quickly and accurately complete the computational phase of valuation.
The Program
This program is written in Reverse Polish Notation (1,5) and calculates tree valuation using the basic formula method. It requires that the user key in tree diameter, species factor, condition factor and location factor. The program internally computes basal area, basic value (the current rate of $27.00 per square inch can be adjusted by changing the entries in program lines 008 and 009), and the net value of the tree. The program presented here was written for use on the Hewlett-Packard HP-11C calculator, but with minor transcriptional changes will work on calculators made by other manufacturers (versions of this program transcribed for the Texas Instruments TI-60, TI-66 and Hewlett-Packard HP-20S and HP-32S are available by contacting the authors).
The probability and ease of use of programmable calculators allow the quick and accurate determination of tree valuation in the field.
A Sample Run
The following example takes the data presented by Neely (3): A tree with a circumference of 47 inches (diameter of 14.96 inches) at height of 4.5 feet, a species factor of 85%, condition factor of 75%, and a location factor of 80%.
Load the program into the calculator according to instructions on Tables 1 and 2.
Key in diameter breast height in inches (14.96 inches), then press the STO key, then press the 1 key.
Key in the species factor as a decimal fraction (0.85), then press the STO key, then press the 2 key.
Key in the condition factor as a decimal fraction (0.75), then press the STO key, then press the 3 key.
Key in the location factor as a decimal fraction (0.80), then press the STO key, then press the 4 key.
Press the f key, then press the A key. The word “running” will flash on the screen for a few seconds, then the net value of the tree as determined by the basic formula method will appear on the display ($2,420).
Operating directions and program listing for computing the monetary value of trees using the basic formula method, for use on a Hewlett-Packard HP-11C programmable calculator.
Program listing to determine tree valuation by the basic formula method using the Hewlett-Packard HP-11C programmable calculatorz
The data entered in the above example will be stored in the calculator for later retrival even if it is turned off. To compute additional tree valuations, new data can be entered and as these data are entered, they override and erase the previous data. If only one tree valuation is conducted, the program can be used for storage of the input values of diameter, species factor, condition factor and location factor. These values can be recalled by using the RCL key. Pressing RCL 1 will cause the display to indicate the diameter, RCL 2 the species factor, RCL 3 the condition factor, and RCL 4 the location factor.
Applications and Use
This program can be used in the field, during the tree’s evaluation, eliminating the need to transport field data back to an office for computation. This allows more rapid evaluation and this can be very important, especially in situations where large numbers of trees are being evaluated. Moreover, use of this program allows more accurate and precise determinations than would otherwise be possible. Not only is the possibility of computational error minimized, but the computational precision is greatly increased. In the illustration given above, for example, the value is $2,437, when using the basic formula method in the traditional manner (3). This is due to the rounding off of numbers during the intermediate steps in the traditional manner of computation. When this program is used, the intermediate figures are not rounded off, and this results in greater measured precision in determination of tree value, since the only point at which numbers are rounded off is at the final stage in calculation.
Footnotes
↵1 Florida Agricultural Experiment Stations Journal Series No. R-00762. Mention of any trade names is for identification purposes only and does not constitute an endorsement.
- © 1990, International Society of Arboriculture. All rights reserved.
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