Understanding Greenhouse Gases in Forestry
Greenhouse gases (noun) - Any gas that limits the escape of heat from the earth's atmosphere.
The three key greenhouse gases in forestry and agriculture are - carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). To understand how greenhouse gases play a role in forestry, it helps to understand how these different gases compare.
Each of the 3 gases has a different global warming potential (GWP), which is a measure of their ability to trap heat in the earth's atmosphere. As CO2 is the weakest of the greenhouse gases, the other gases are compared to CO2 as a factor of how much stronger they are. This is known as CO2 equivalents (ie, CO2e).
|Carbon Dioxide||Methane||Nitrous Oxide|
|CO2 = 1 CO2e||CH4 = 25 CO2e||N2O = 298 CO2e|
These gases are often associated with a variety of processes in agriculture and forestry.
CO2 is emitted whenever organic matter is burnt or decomposes, but is also absorbed by plants as they grow, converting it to carbon and using it to create plant tissues and energy. By virtue of their size and longevity, trees can absorb significant amounts of CO2.
CH4 is released as a part of organic decomposition and ruminant livestock production (beef & sheep).
N2O is produced when nitrogen fertiliser or urine are exposed to the atmosphere. N2O emissions are common in livestock or fertilised industries.
Comparing forestry and agricultural emissions
In contrast to other agricultural systems, forests often act as a greenhouse gas sink for two reasons.
Forests emit relatively few greenhouse gases
Under typical growing conditions, forests emit very little CO2 and CH4. Even when fertiliser is applied, N2O emissions are small considering the application usually takes place only once or twice over a forest's lifetime. Fire can result in a large loss of CO2 stored in a forest.
Forests absorb large amounts of greenhouse gases from the atmosphere
Any emissions from forests are often counteracted by a trees' ability to absorb CO2 as they grow. Absorption of CO2 will continue from establishment through to maturity. At maturity, net gain of CO2 in the trees will stop, and other CO2 accumulation may continue (eg, soils).
Because of the ability of forests to absorb CO2 and emit very few greenhouse gases, they can be a very effective at reducing emissions compared to other agricultural businesses.
Emissions of CO2e t/ha/yr (Indicative only)
Calculating a forest's emissions
Calculators are available for forest managers interested in estimating the greenhouse gas profile of their forests.
Developed to calculate the emissions profile of many forest types, factoring in location, species and management practice. Although it can be challenging for some users, a guide is available online and the calculator produces figures that are likely to be used in an official carbon trading scheme. Click on the link to order a CD copy.
This calculator is designed for mixed farming businesses, calculating emissions from animal and plant production systems in addition to environmental tree plantings on the farm. The calculator is downloadable.
For more information on measuring and reducing emissions in agriculture, go to DPI's Carbon Toolkits in Agriculture Network page.