Mountain Ash Forests as Carbon Sinks
Old growth Mountain Ash tree
Photographer - Ross Field
The Mountain Ash forests of the Victorian Central Highlands contain the world’s highest known biomass carbon density, or stored carbon. This is particularly so for 'old growth' stands containing Mountain Ash trees between 100 and 500 years of age.
These forests have high carbon stocks for a number of reasons:
- Characteristics of individual trees
Mountain Ash are evergreen, with some growth occurring throughout the year. Mountain Ash wood is extremely dense, enabling storage of large amounts of carbon, and the trees grow to over 100m tall and 6m in diameter.
- Characteristics of the forest environment
Mountain Ash trees have a thin canopy which allows a luxuriant evergreen understorey to flourish. Typically they grow where there is high rainfall (1670mm, O’Shannassy catchment) and deep fertile soils that encourage rapid growth. Mountain Ash trees usually grow on a southerly aspect with a cool mean annual temperature (9.4 degrees C, O’Shannassy catchment). These cooler wetter conditions contribute to long intervals between wildfires, with fires that do occur being relatively less intense.
- Land Use
Human activity has had little impact on those old growth Mountain Ash forests remaining intact today. They have not been subjected to timber harvesting, or land management practices like the Indigenous firestick farming undertaken in many other forest types in the past.
This means the loss of carbon through decomposition and respiration is lower than the rate at which it is gained through plant growth. In old growth forests this ‘net gain’ of carbon has been occurring for hundreds of years.
Reference: Keith, H., Mackey, B.G. & Lindenmayer, D.B., 2009, Re-evaluation of forest biomass carbon stocks and lessons from the world’s most carbon-dense forests, PNAS (http://www.pnas.org/content/early/2009/06/24/0901970106.abstract)