VALUE- ADDED GREEN­ERY

The Weekend Post - Cairns Eye - - Front Page -

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!

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