As far as I know, the first scientist to attempt estimating the monetary value of a tree was' Professor T M Das of the University of Calcutta. His paper was published in Indian Biologist, Vol XI, No. 1-2, 1979. He considered that the total weight, quality of timber, fruit or biomass amounted to about 0.3% of the real value of a tree.

Prof Das's system looked at a number of factors, one of which was oxygen production. The net accumulation of one gram of carbon in a tree was compared with the net production' of 2.66 g of oxygen. This oxygen production was related to the weight of a tree, using a correction factor for the amount of leaf shed every year and the age of the tree. The oxygen was valued at the prevailing Indian market rate.

Oxygen value

Prof Das subsequently reported that his work in the United States with infra-red gas analysis gave more or less the same result of the net oxygen production of a tree.

Using his figures, with an adjustment for inflation, and conversion to Australian dollars, I estimate-a medium size tree produces about $30,000 worth of oxygen over 'a period of 50 years.

Prof Das assessed that a tree in India could feed a pair of goats and he estimated that this conversion to animal protein would total' around $2000 over 50 years.

The other factors he costed out,: based on "repeated observations and ' comparisons with available data from the scientific literature" included controlling soil erosion and soil fertility $30,000; recycling of water and controlling humidity $36,000 sheltering birds, animals, other piants etc $30,000, and controlling air pollution $60,000. Theis gives a total for the 50 years of $188,000.

The US Council of Tree and Landscape Appraisers has created a formula for estimating tree worth. This system assigns a basic value according to the diameter of the tree trunk. Using this formula, a healthy tree in ' a park with a 100 cm diameter trunk could have a value of more than $120,000.

A tree planted in the wrong place, for example, under electricity wires, does not have the same value as a free-standing one, but even a dead,tree is assigned some value because it attracts certain birds and animals and without these 'hotels' you would soon notice the unhealthy silence of a bird-free city.

The Australian Institute of Horticulture Inc has published a pamphlet entitled A Sysfem of Assigning a Monetary Value to Amenity Trees. (E J McAlister, FAIH, 1990).

The formula considers' how rare or common the tree is, historical significance, location, form and vigour, live crown size and life expectation. I calculated that a mature Eucalyptus pilularis in my yard, which is about 50 years old, has a value of about $70.00.

Peter Thyer of Manly Municipal Council has devised another system which considers more factors. On my calculations, his formula also gives a value of less than $10,000 for that particular eucalypt.'

The US Forest Service estimates that market values for homes are increased by the presence of trees at rates ranging from seven to 20%. Apart from homes on the coastline, you will generally observe that the more expensive urban homes are in areas which have plenty of trees.

Of course, to a large extent all the tree valuation calculations are theoretical, they relate to the philosophy of the scientist and are largely based on the supposition that the tree species is appropriate to the locality.

Valuations from different countries are not really comparable, but it's interesting to ponder why the Australian systems assign a tree value of 'less than one-tenth of the Americans and about one-twentieth of the Indian scientist. It is a reflection of the relative population densitites? .

India'has 3,287,263 square kilometres' of land to support a population of over 850 million; US 9,372,614 to support 247 million and Australia 7,682,300 to support 17 million people. Perhaps it is a reflection of how Australian horticulturists rate the results of their work? If you can spread comprehensible information about the silent, uncomplaining, nonpolitical' work of trees and other plants, the public may eventually be prepared to pay more to get quality information and quality plants.

Trees and plants silently carry out their daily routines year after year, stabilising the soil, recycling nutrients, cooling the air, modifying wind turbulence, intercepting the rain, absorbing the toxins, reducing fuel costs, neutralising sewage, increasing property values, enhancing, social awareness, providing beauty, cutting noise, giving privacy, promoting tourism, encouraging recreation, reducing stress, and improving personal health as well as providing food, medicine and accommodation for other living things.

Trees: quiet achievers

Some trees are clever: they can communicate with each other, do arithmetic, tell time, display affection, align themselves according to magnetic influences, predict changes in the weather and even produce their own rain. Like humans, they can survive fire, drought, floods, storms, hunger and loss of limbs.

Trees are symbols of dignity, endurance and adaptation; they fight back rather than give in, they have an irresistible urge to exist, to reproduce and to develop. They usually overcome the excesses of civilisation and they want to live to maturity.

Trees were already forming in large forests 330 million years ago, and the first humans came into existence about 327 million years later. It is clear, we're parasites on them. In a natural environment, plants are producers while people and animals are consumers.

A linden tree in Germany is over 600-years old and a few cedars of Lebanon are estimated to be 2000 years of age.

The largest known tree in the world was estimates to have a height of 140 m and a girth of 50 m. Trees are the only living things with enough mass harmonise with the excesses of civilisation.

Prescribing trees may not fix all that's wrong with our towns and cities, but tree planting could be promoted as a contribution that individuals can make to clean up the environment and to reduce stress. It's unlikely that a tree valuation formula will ever be devised that is acceptable to everyone, but the principle is that our green assets are valuable in diverse and subtle ways.

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