Sequestering Carbon in Native Forests Part IV

Here’s the next instalment of the Sequestering Carbon in Native Forests series. It’s fairly acedemic (I have to be serious sometimes), so get your acedemia on! If you haven’t read any of the previous posts in the series maybe check them out first; they are best read in order.

Pre-existing forests can be managed to sequester carbon through measures such as having a mix of species, managing fire regimes and keeping the forest at an ideal mix of age-classes. A mixture of species in a forest makes the system more resilient and overall better at storing carbon (Böttcher and Linder, 2010).

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This plantation looks really cool but in terms of sequestering carbon it’s not great as it doesn’t have a mix of species or age classes. PHOTO: wood report

 

As outlined above, different species react differently to factors such as water availability so in this way a resilient tree community would be made up of a variety of species so that whatever the rainfall pattern at least one species was still able to actively sequester carbon.

In the Australian bush the constant possibility of fire means that landholders with a large number of trees on their property need to have a fire management plan with efforts such as controlled burning to reduce fuel loads. (Böttcher and Linder, 2010).

Although this releases carbon dioxide, it can greatly reduce the risk of large, uncontrolled fires later and can actually help with the sequestration process if the ash goes back into the soil. For the purposes of sequestration the ideal age-class structure of a forest is fairly mixed (Böttcher, 2007).

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Controlled burns are important in Australian forest management. PHOTO: abc.net.au

If a system cannot self-regulate to achieve this, the forest should be managed; trees that are all relatively young and still growing sequester large amounts of carbon but there will be a lesser extent of the natural process that use dead roots, branches and twigs to lock up carbon in the soil as these processes take decades to fully establish.

However, if the forest comprises only of mature trees that have stopped growing the sequestering potential for that forest will largely have been reached.

Thus, once a forest has been established it should be managed (if it can’t self-regulate) so there is a mixed age-class with a mind to disturbing the ecosystem as little as possible. While it takes around 100 years for this point to be reached (possibly longer in low rainfall areas) the potential of forests to mitigate against climate change, even in those low rainfall areas, is good.

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Sequestering Carbon in Native Forests Part III

Using trees to sequester carbon in low-medium rainfall areas has high potential because those areas are not widely used for agriculture and often are in need of regeneration.

However, which species can be planted will depend on the amount of water available and how specific species react to factors such as long drought periods, sudden floods and random cycles of wet and dry periods.

The main species used for sequestration are eucalypts, most of which have various adaptations to Australia’s unpredictable weather patterns but a tree that is stressed due to lack of water will stop growing, thus stop sequestering carbon, and may even die.

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An eight year old planting of e. sideroxylon. PHOTO: NSW Department of Primary Industries.

A study done by Walsh et al (2008) found that E. globulus and E. botryoides are both highly suited to sequestering carbon, but while both species can sequester during short periods of little or no rainfall neither can handle extended drought, which is all too common in low rainfall areas during el Niňo years. This makes those species suitable but not ideal.

The same study found that while E. camaldulensis, E. sideroxylon and C. maculate are not as efficient in sequestering carbon they can handle long periods of drought far better than the above two and so are better suited to low-medium rainfall conditions. This shows that while it is not ideal to plant in such conditions compromises can be made.

Above all, it is important that these planted forests are not competing for land with agriculture or pre-existing forests.

Of course, unlike plantations, these forests need not be in one big clump; they can be spread along fence lines or creeks, they can be a patchwork across paddocks or public land, anything so long as they are large enough (≥0.2 ha) to qualify as a forest. Spacing plantings like this can also minimise water needed in any one place (Battaglia, 2011).

If you want to learn more about eucalyptus plantings, the NSW Department of Primary Industries has a lot to say on the issue.