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Oxygen: Grass vs Trees
Name: Mike
Grade: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Given the replacement of some native forested areas (East
Texas) by intensively farmed facilities (year round farming) is
grass going to produce more oxygen per unit area of land than the
trees removed?
Replies:
The following may be helpful.
http://www.newton.dep.anl.gov/askasci/bot00/bot00775.htm
Anthony Brach Ph.D.
Hi,
and thanks for the question.
Does grass produce more oxygen than trees? I think yes and no.
A field of grass might generate more mass of grass in a year than the equivalent
addition of mass in a similar area of forest. It would depend a geat deal on the
specific species of grass and forest plants you are trying to compare.
What is more important in the long run is the NETT production of oxygen. Oxygen is
being produced and used up at the same time. What we need to consider is the
overall change. Do we produce more than we use up ( a NETT GAIN) , or do we use up
more than we produce? (A NETT LOSS)
In order to see a NETT production of oxygen, we must also see a NETT production of
carbon products - noticibly wood. Wood represents the locking up of the Carbon
extracted from CO2 in order to release oxygen. So forests produce lots of wood,
they must also produce lots of oxygen - which is true.
Grass on the other hand produces no wood. Its carbon is turned into carbon products
such as sugars, starches and cellulose. These are all good carbon products, and
represent a production of oxygen, and they are all produced by the forest plants as
well.
The problem is in the next step - what happens to the grass?
If it is left on the ground it rots, and uses up oxygen as the sugars and starches
and cellulose rot and release CO2 again. By equivalence, the forest may lose all
its leaves in fall.
If the grass is eaten by a cow, then the cow uses oxygen to 'burn' the grass as
fuel, and produces CO2. Similarly, parts of the forest plants are eaten - fruits
berries leaves etc.
Either way, the NETT production of oxygen in a field of grass is very small,
because the carbon products are not as long lasting as wood is.
This locking up of carbon is a hot topic at the moment, with terms like carbon
banks and carbon sequestering and carbon trading. By locking carbon up, either in
living forests or as underground reserves of CO2, we are helping to reduce CO2 in
the atmosphere, and hopefully reducing the greenhouse effect which is helping to
drive global warming. Industries which produce a lot of CO2 by burning coal and
oil etc, can offset their emissions by investing in the planting of carbon bank
forests. The effectiveness of this strategy is debated though. To offset the
emissions resulting from the production and burning of 1 gallon of ethanol
(biofuel) you would have to grow approximately 10 pounds of timber - (not including
leaves etc.) To make the offset effective, you have to grow 10 pounds of WOOD for
EVERY gallon of ethanol. That's a 5000 lb tree for every car every year. If you
keep using petrol or gasoline, the tree has to be even bigger!
Nigel Skelton
Tennant Creek
AUSTRALIA
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Update: June 2012
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