Planting trees continues to be an effective greenhouse tactic

A multidisciplinary team from the Cooperative Research Centre (CRC) for Greenhouse Accounting, the Australian National University, CSIRO, Ensis and the University of New South Wales has reaffirmed the value of tree planting to mitigate greenhouse gas emissions.

In the paper, A Comment On The Quantitative Significance Of Aerobic Methane Release By Plants, published in the journal Functional Plant Biology the research team questions some findings of a recent study published in the journal Nature which demonstrated that living and dead plant tissues emit methane " a major greenhouse gas. The Nature article led various commentators to question the value of planting trees as a greenhouse mitigation option.

"While the experimental work of Keppler et al. appears to be largely sound, we found some serious flaws in the method used for extrapolating results to a global scale," says the CRC's Dr Miko Kirschbaum.

"Our alternative calculations concluded that much smaller amounts of methane from plants would be emitted globally if the methane production mechanism were confirmed. These estimates make much more sense, given our understanding and the remaining uncertainties in the established sources and sinks in the global methane budget."

The benefit from carbon sequestration is 100 times greater than any offset from the proposed methane emissions.

CSIRO Plant Industry Research Scientist Dr Roger Gifford says the team also assessed its findings in terms of their possible relevance for planting trees as a greenhouse mitigation option.

"Our work concluded that methane emissions from plants by the newly described mechanism would reduce the benefit of planting trees by between zero to 4.4% if it occurs in the field," Dr Gifford says. "The benefit from carbon sequestration is 100 times greater than any offset from the proposed methane emissions."

The paper notes that there is much critical information still lacking, including: knowledge of the underlying mechanism for aerobic methane emission; how methane emissions change with light, temperature and the physiological state of leaves; whether emissions change over time under constant conditions; whether they are related to photosynthesis; and, how they relate to the chemical composition of biomass.

"The present calculations must be seen as a preliminary attempt to assess the potential global significance of the results found by Keppler et al. on a basis of limited information," Kirschbaum says. "They are likely to be revised as further information becomes available. One thing, however, is known: planting trees is not a waste of time. It is an effective way of slowing climate change."