VALUE- ADDED GREENERY
Real estate agents will tell you a garden adds about 10 per cent to the value of a house. This is true; look at a house with a nice garden and one without. Equations have been around for a long time to ascribe a value to plants. In fact, there have been some great attempts at a method of valuing a tree.
In 1992 the American Forestry Association found a single tree provides $73 worth of airconditioning, $75 worth of erosion control, $75 worth of wildlife shelter and $50 worth of air pollution reduction. Compounding this total of $273 for 50 years at 5 per cent interest results in a tree value of $57,151.
The Australian Institute of Horticulture has had a system of assigning a monetary value to amenity trees for some years and it is often the method that is behind the evidence presented in courts by expert witnesses to demonstrate the monetary value of a tree.
This method takes a few elements into consideration such as how often the tree occurs in the landscape, if it has historical association (like the Tree of Knowledge at Barcaldine), its location, and its form and vigour. The live crown of the tree is also considered.
If you see a tree with lots of dead terminal sticks in its crown, there is something wrong. Other trees with a leafy and complete crown are healthier.
Each of these factors is given a score — a method that has been scientifically formulated to lead to a dollar value. The total of the scores is multiplied by the cost of the same juvenile tree purchased from a nursery to arrive at a value — in many cases between $50,000 and $100,000.
One of the famous tree value posters is on the internet and is produced by a Professor Das of the Michigan State University. The professor says a 50-yearold tree will produce $32,000 worth of oxygen, recycle $37,000 of water, provide a habitat for animals worth $31,200, and $62,500 worth of air pollution control, erosion management and soil fertility.
Taking these factors into consideration he provides a general value of $193,250. Presumably he has devised a method or formula to arrive at these figures. He mentions but does not provide any information on the value of fruit and other by-products (such as rubber, maple syrup, leaf litter and mulch, and other items).
We don’t need to see how the formulae work or what they may be; it is a fact of life that you can attach a dollar value to a tree as it exists at any stage of its life. The next exercise is working out its age!