Tree Appraisal of McKeldin Mall Oaks
Trees Have a Value
Tree Appraisal of McKeldin Mall Oaks
How 129 Oak Trees can be worth $3.53 Million
The Trunk Formula Method can be used to appraise the monetary value of trees when they are considered too large to be replaced with nursery or field grown stock (Bloch, 2000). This size consideration applies to the trees forming the double allee surrounding McKeldin Mall. The input variables for this estimation method include: Location, Species Rating, Condition, Size, and Installed Tree Cost.
Location Percent The mean of Site Percent, Contribution Percent, and Placement Percent. A Site Rating of 90% was used due to the significance of McKeldin Mall and the surrounding trees. A Contribution Rating of 85% was used because the trees play a major part in forming the image of the space known as McKeldin Mall. A Placement Percent of 80% was used since the trees do receive regular pedestrian traffic in the critical root zone, which causes compaction, and there is a significant amount of concrete sidewalks which may limit root growth. McKeldin Mall is used by many in the UMD community as a sanctuary from summer heat, as a place to study and gather thoughts, and as a place of transit to get to the next class or appointment. The mean of these factors yields a Location Percent of 85%.
Size This is based on a measurement of the diameter of the tree at breast height (DBH) or 4.5’ off the ground. DBH was collected in March 2011. This diameter is used to calculate trunk area (TA) in inches squared. A quadratic equation supplied by The Guide for Plant Appraisal is used on any tree with a diameter over 30” to calculate an adjusted trunk area (ATA). Diameters range from 4” to 49.7” at breast height for these trees.
Condition Percent The Condition Rating is based on the Appraiser's experience and takes into account the history of the trees and site along with the overall health of the specimen. These oaks were given a conservative Condition Rating of 80% based on the fact that all of these trees were crown cleaned to remove deadwood, crossing branches, water sprouts, diseased branches and the soil was injected in the summer of 2010 with fertilizer and mycorrhizal inoculums. Note that these trees are ~90 old so regular maintenance becomes a factor, overall the trees are in good health.
Species Rating Quercus phellos (Willow Oak) and Quercus nigra (Water Oak) have an established species rating of 60% -90% within the Mid-Atlantic Region. This rating is set by the Mid-Atlantic Tree Species Rating Guide published by The International Society of Arboriculture. 85% was used as the input for the Species Rating for this appraisal. McKeldin Mall boasts 128 Quercus phellos and 1 Quercus nigra. Quercus phellos is the most common tree on campus, and has performed exceptionally well in our urban forest.
Installed Tree Cost This rating is based on the Mid-Atlantic Tree Species Rating Guide. This guide uses the largest commonly transplanted tree in the Maryland and Virginia area (5 inches in caliper). Other input figures are as follows: Cross-Sectional Area is 20 square inches, Replacement Tree Cost is $500, and Installed Tree Cost is $1500 which gives a Unit Tree Cost of $75 per inch. For this exercise, the ratings of Location, Species and Condition are the same for all 129 Oaks. However, Size was calculated on a tree by tree basis. Based on the variable inputs and the data of tree DBH’s collected, the overall value of the 129 oaks is estimated at $3.53 Million.
Bloch, L. 2000. Guide for Plant Appraisal 9th Edition. Champaign, IL.
International Society of Arboriculture. 2007. Mid-Atlantic Tree Species Rating Guide. Earlysville, VA.