Research looks at native trees and carbon emissions

20 June 2007

Are our native trees adding to or reducing New Zealand’s carbon emissions? That’s the question Rotorua scientists are hoping to answer with one of their current research projects.

Two projects investigating native trees and carbon emissions are underway at Ensis, the unincorporated joint venture between Crown Research Institute Scion in Rotorua, and Australia’s CSIRO.

Dr Peter Beets, senior scientist at Ensis, is leading a research programme looking at developing tools to predict native tree carbon emissions.

“Our aim is to work out the amount of carbon that is being absorbed by living trees and the amount of carbon that is being released when trees die and decay.

“We hope to find out if native trees actually reduce the country’s overall emissions at all, or if the emissions the trees make just cancels any benefit,” Dr Beets says.

Estimates of carbon emissions for New Zealand’s indigenous and exotic forests must be reported to the United Nations because the country has signed on to the Kyoto Protocol.

Dr Beets’ government-funded research programme involves learning how quickly various species of native trees – including Matai, Rimu, Red Beech, Silver Beech, and Tawa – decay.

“It is difficult to work out decay rates because it can take decades to get data on trees that have only fallen down today. So instead we are going into areas where a known event has happened – for example Cyclone Bernie – and using those trees to come up with data from the last 20 or so years.

“Preferably we go to areas where historical data has been collected, so that we can build on that work. For example, one of our plots is at Whirinaki Forest where tree mortality was assessed in 1983 and 1997,” Dr Beets says.

Samples from live trees and  dead logs in Whirinaki Forest, Taranaki Region, Kaimanawa Forest and Mount Maungatautari are being dried, weighed and the volume and density measured. These samples are compared to understand the decay rate and produce a measurement of carbon that is released from the trees.

The team is also using ‘graveyard data’ – historical data gathered throughout New Zealand about the decay rates of many indigenous trees.

“The graveyard data and our own work is enabling us to rank species decay rates – some species such as red beech can take about 30 or more years to rot, while others take less than 10. That has a big impact on how long it takes for trees to release carbon into the atmosphere.”

Dr Beets says models for tree decay and carbon emissions have already been developed for forest plantations, and this research aims to do the same for indigenous forests.

“The idea is that we don’t want vast amounts of money spent on trying to measure forest sinks and emissions, so instead we are coming up with tools that make an accurate prediction,” Dr Beets says.  

Ian Hood, Forest Pathologist at Ensis, is working on a closely linked project looking at fungi that cause decay in native trees which leads to carbon release.

“Peter’s work is looking at the amount of carbon that is being absorbed by living trees and the amount that is released. My work is specifically looking into the fungi that grow on decaying native trees to see if this has any effect on the rate of decay.”

Mr Hood’s study looks at eight rimu and eight matai trees that fell during a storm in 1982 in the Whirinaki Forest. As the fungus decomposes the tree, carbon is released into the atmosphere. Mr Hood is investigating which are the main species of fungi that cause most of the decay.

The next step for Mr Hood’s project is to see if there are regional differences in decay which can be explained by the presence of other fungi or by other factors such as increased warmth or moisture in a region.

“Already a related study in a nearby beech forest is revealing a different population of fungal decomposers,” Mr Hood says.

The work by Ensis scientists is aimed at building up a better understanding of the role native forests play in carbon emissions.

“We know when these trees fell, so from that we can learn how long the decay takes and estimate the carbon release that is caused.

“New Zealand has a responsibility under the United Nations Framework Convention on Climate Change to report on carbon sources and sinks – and that includes from our native forests. There’s still a lot of work to be done, but the research by the Ensis team is bringing us closer to knowing what role our forests play,” Dr Beets says.