Submitted to: Journal Of Arboriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/1996
Publication Date: N/A
Interpretive Summary: Tree appraisers, arborists and foresters have been using species values that were subjectively assigned by a group of experts in 1970. The problem with this system of species rating is that it gives a wide range of values to every species. This translates to very divergent appraisals by two or more arborists of a tree in question. Some places have recently developed their own species values but still showed a wide range of values for any given species. To eliminate this bias due to species, we developed a system that establishes a single value for a given species using tree characteristics that are quantifiable and inherent, such as, flood tolerance, pollution tolerance, specific gravity, longevity and others. The individual values of 63 tree species growing in Louisiana landscapes were derived, and these ranged from 47% for yellow poplar to 93% for live oak. With this new system, tree appraisers will have an easier time evaluating trees, and assessed values of a given tree by two or more appraisers will be very close if not consistent. This system of species values can also be very useful to anyone selecting a tree to plant in his or her own yard. More importantly, values of species in other parts of the country can be established using this procedure.
Technical Abstract: For many years, Louisiana arborists have been using the 1970 species rating developed by the Shade Tree Conference, Inc. for the southern region of the United States. This rating was subjectively derived and could potentially give 20% differentials in basic values within species, suggesting that an appraisal of the same tree by two or more arborists could differ by as much as 20%. Add to this the compounding effects of condition and location, and you have appraisal values that are outrageously different. This project was initiated to eliminate bias in tree appraisal due to species. The species ratings of 63 Louisiana trees (based on the ISA Arborist Certification Tree List for Louisiana) were derived using quantifiable and inherent characteristics of each species: pollution tolerance (ozone, landfill and sulfur dioxide), flood tolerance longevity, pest prevalence, specific gravity, and soil compaction tolerance. Some of the derived values were closely similar in magnitude to the 1970 values, but most of them were different. Derived values ranged from 47% for yellow poplar to 93% for live oak as opposed to 20% for shortleaf pine to 100% for red maple with the 1970 rating. We recommend the use of these derived specific values, rather than ranges, to eliminate appraisal bias due to species.