The Value of a Tree
How much do YOU think a tree is worth?? And how does one measure the value
and then convert the result to monetary terms? Here's one way.....
When Sue Rostas, Communications Officer for the Kooragang Wetland Rehabilitation
Project, received a letter from Carrington Public school student, Michael Wilson, it set
her thinking.
Michael asked what was the economic value of a tree. He suggested we assume a value
of $1 a day for the amount of oxygen that a tree produces. A tree thus produces $365
worth of oxygen per year or a total of $36,500 over 100 years (and that's not allowing for
inflation!)
Sue wondered how close to the mark was this assumed dollar value. A few phone calls to
Assoc. Prof. Tlna Offler, University of Newcastle, and Bill Nethery, State Forests of
NSW, plus some library work revealed some startling but often overlooked facts about
the true value of trees.
Michael's assumption had in fact greatly underestimated the value of trees. The true value
(considering only oxygen output) of a tree such as a Red Cedar would be about $120,000
each year (see box below). If the tree lived 50 years, it would have produced about $6
million worth of oxygen!!
The world would indeed be in deep economic trouble if we had to pay for the oxygen a
tree produces.
This calculation of the value of a tree has been based solely on its net oxygen output. But
trees also have economic value in a number of other ways:
• They reduce the water table level and hence reduce soil salinity, which in turn
improves the soil's ability to grow plants.
• They act as a carbon sink, using up considerable quantities of carbon dioxide, thus
reducing the level of greenhouse gases in the atmosphere.
• Oh, and by the way, they produce a valuable building material - timber.
A 50-year-old Red Cedar would yield about $5000 worth of timber - this is the only
factor usually considered when determining the economic value of a tree. As you can see,
this pales into insignificance compared to the value of the oxygen the tree gives us free of
charge !
Commercial cost of oxygen
7.9 litres (9.0 kg) of oxygen costs $54.
From this we can calculate that 5 mole oxygen costs $1.
Value of net oxygen output of a tree such as red cedar
• Trees produce approx 5 mole (a measure of the number of
molecules) oxygen per square metre leaf area per day.
• Trees use about half this oxygen for their own respiration.
Therefore, the net oxygen output of a tree is approx 2.5 mole
per square metre leaf area per day.
• For tropical rainforest the average total leaf surface area is
about 8 times the area of the canopy.
• A 5 year old red cedar has a canopy of about 7 square metres
and hence a net oxygen output of 2.5 x 8 x 7 = 140 moles worth
$28 per day (about $10,000 per year).
• A 20 year old red cedar has a canopy of about 80 square metres
and hence a net oxygen output of 2.5 x 8 x 80 = 1600 moles
worth $320 per day (about $120,000 per year).
• By the time the tree is 50 years old it would have produced
oxygen worth about $6 million!
NB The above calculation is a rough estimate assuming 10 hours of
sunlight per day and "typical" levels of water, light, temperature and
nutrients.
Media Release of 24 July 1998 by the Kooragang Wetland Rehabilitation Project, Newcastle, New South
Wales.
and then convert the result to monetary terms? Here's one way.....
When Sue Rostas, Communications Officer for the Kooragang Wetland Rehabilitation
Project, received a letter from Carrington Public school student, Michael Wilson, it set
her thinking.
Michael asked what was the economic value of a tree. He suggested we assume a value
of $1 a day for the amount of oxygen that a tree produces. A tree thus produces $365
worth of oxygen per year or a total of $36,500 over 100 years (and that's not allowing for
inflation!)
Sue wondered how close to the mark was this assumed dollar value. A few phone calls to
Assoc. Prof. Tlna Offler, University of Newcastle, and Bill Nethery, State Forests of
NSW, plus some library work revealed some startling but often overlooked facts about
the true value of trees.
Michael's assumption had in fact greatly underestimated the value of trees. The true value
(considering only oxygen output) of a tree such as a Red Cedar would be about $120,000
each year (see box below). If the tree lived 50 years, it would have produced about $6
million worth of oxygen!!
The world would indeed be in deep economic trouble if we had to pay for the oxygen a
tree produces.
This calculation of the value of a tree has been based solely on its net oxygen output. But
trees also have economic value in a number of other ways:
• They reduce the water table level and hence reduce soil salinity, which in turn
improves the soil's ability to grow plants.
• They act as a carbon sink, using up considerable quantities of carbon dioxide, thus
reducing the level of greenhouse gases in the atmosphere.
• Oh, and by the way, they produce a valuable building material - timber.
A 50-year-old Red Cedar would yield about $5000 worth of timber - this is the only
factor usually considered when determining the economic value of a tree. As you can see,
this pales into insignificance compared to the value of the oxygen the tree gives us free of
charge !
Commercial cost of oxygen
7.9 litres (9.0 kg) of oxygen costs $54.
From this we can calculate that 5 mole oxygen costs $1.
Value of net oxygen output of a tree such as red cedar
• Trees produce approx 5 mole (a measure of the number of
molecules) oxygen per square metre leaf area per day.
• Trees use about half this oxygen for their own respiration.
Therefore, the net oxygen output of a tree is approx 2.5 mole
per square metre leaf area per day.
• For tropical rainforest the average total leaf surface area is
about 8 times the area of the canopy.
• A 5 year old red cedar has a canopy of about 7 square metres
and hence a net oxygen output of 2.5 x 8 x 7 = 140 moles worth
$28 per day (about $10,000 per year).
• A 20 year old red cedar has a canopy of about 80 square metres
and hence a net oxygen output of 2.5 x 8 x 80 = 1600 moles
worth $320 per day (about $120,000 per year).
• By the time the tree is 50 years old it would have produced
oxygen worth about $6 million!
NB The above calculation is a rough estimate assuming 10 hours of
sunlight per day and "typical" levels of water, light, temperature and
nutrients.
Media Release of 24 July 1998 by the Kooragang Wetland Rehabilitation Project, Newcastle, New South
Wales.
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