Species Ratings & Appraisal Factors for Illinois

For use by qualified professionals in conjunction with the Nineth Edition of the Guide for Plant Appraisal published by the International Society of Arboriculture

The Illinois Arborist Association Tree Appraisal Committee that worked very hard to develop the information in this booklet consisted of:

• Bill Bolt (Chair), Consulting Arborist

• Stan Holat, Autumn Tree Care Experts

• Terry Cichocki, Village of Northbrook

• John Kirchner, City of Chicago

Special thanks also to Galen Gates at the Chicago Botanic Garden and George Ware at the Morton Arboretum for their assistance in updating the species ratings, and to our colleagues in adjacent states who form a regional committee, which assures continuity across state lines.

NOTE: The information given in this booklet will be reviewed and updated at appropriate intervals. If a change is made, it will be published by the Illinois Arborist Association, a Chapter of the ISA, in a method determined by the Board of Directors. If you are not sure of the latest information, call the Chapter office at (877) 617-8887.

INTRODUCTION

The Guide for Plant Appraisal (9th Edition) specifies that "for these appraisal methods to be effective, relatively easy to use, and widely accepted in a region, a group of horticultural professionals should be the ones to determine, keep updated and publish"

• Species ratings

• Largest commonly available transplantable tree

• Average cost of tree replacement, and

• Cost per unit trunk area.

Species ratings are based only on species characteristics, without regard to condition or location. Factors considered were environmental adaptability, biological traits (i.e. growth rate, pest resistance), maintenance requirement and aesthetic characteristics. Condition and location factors related to these species characteristics must be considered carefully. For example, pin oak has limited environmental adaptability with regard to soil type, and this contributes to its 70 percent rating. However, when planted in alkaline soil, the site component of the location factor would have to be rated low. Condition of the tree might be poor as well.

The information on this website should be accurate for most situations. However, individual situations may be unusual. Occasionally, characteristics of an individual tree or cultivars may be superior. Microclimate variation can occur. The professionals using this booklet in conjunction with the Guide for Plant Appraisal may occasionally find that their own judgment calls for alteration of this generalized information.

Illinois is nearly 400 miles long from north to south. The climate for growing trees varies considerably within the state. The USDA Plant Hardiness Zone Map was used to divide the state into three regions, corresponding to hardiness zones 5a (north), 5b (central), and 6a (south). See USDA Miscellaneous Publication Number 1475 for more details on hardiness zones.

There are essentially two categories of information in the Species Ratings Guide & Appraisal Factors for Illinois and this sometimes leads to confusion.  Since the initial publication in 1994 there have been two updates to the Appraisal Factors; in 2001 and 2005.  The methods for determining these factors are set forth in the Guide for Plant Appraisal and are the factors are updated periodically to reflect current market conditions.  The original Species Rating Percentages for Illinois have not changed.

A survey of Illinois Green Industries is used to gather the data for the Appraisal Factors which include the largest commonly available transplantable sized tree, the installed and guaranteed cost of the largest commonly available transplantable tree, and the basic cost or unit tree cost per unit of trunk area ($ per square inch).  These values are used along with the Species Rating Percentages in the Trunk Formula Method of plant appraisal.  The Appraisal factors (except the unit tree cost) and the Species Rating Percentages are also used in the Replacement Cost Method outlined in the 9^th Edition of the Guide for Plant Appraisal.

It is important to understand that the published Appraisal Factors and Species Rating Percentages are generally agreed upon values that can be used to calculate appraised values for landscape plants.  Appraisers can and often do calculate the Appraisal Factors based on their own research which may be more precise in specific cases.  The Guide for Plant Appraisal incorporates some flexibility in how the Appraisal Factors are determined and the decisions made by the committee may not reflect local conditions.  It is also legitimate for an appraiser to substitute his or her own Species Rating Percentage(s) based on local conditions and expertise of the appraiser.  If substitute values are used by an appraiser, he or she should expect to be called upon to explain how they were determined and to justify them if the appraisal is challenged.

  Click here for a map of the regions