DECOMPOSITION OF DEADWOOD DEBRIS LEFT OVER FROM TROPICAL RAINFOREST LOGGING OPERATIONS

Lead Research Organisation: Imperial College London
Department Name: Life Sciences

Abstract

The widespread and rapid logging of tropical forests may mean their global carbon emissions have been underestimated because they do not fully account for the dead wood left behind.

Living trees take in carbon dioxide whereas dead and decaying ones release it. It is the balance between these two processes that determines whether a large area of forest is a source of carbon dioxide, or a 'sink' that helps to absorb carbon dioxide from the atmosphere. Partially-logged tropical rainforests are probably emitting more carbon than assumed because they contain a high proportion of dead wood. Loggers will typically leave around one quarter of all the trees they cut, or that get damaged during logging operations, to rot in the forest. This dead wood can make up almost two third of the biomass, the biological material found above ground, in logged forests. Compare that proportion to untouched forests, where dead wood is created through natural processes, and where it makes up around 20 per cent of the total aboveground biomass.

Around one third of all tropical forests have been logged and that proportion is increasing rapidly, meaning tropical forests contain much larger amounts of dead wood than previously thought. Learning how rapidly that dead wood will decompose is a key ingredient for calculating the carbon balance of tropical forests. And the carbon balance of forest could, in turn, hold the key to combating climate change.

We don't know if dead wood in a logged forest will take longer to decompose than dead wood in an untouched forest, and getting that answer is a complicated business. Not only do we need to know how fast the dead wood left behind by the loggers will decompose, we also need to know how fast new pieces of dead wood are created. And logged forest creates a lot because the trees left behind in logged forests live and die faster than the trees the loggers take away, and when they die they turn into dead wood. One of the reasons these trees live and die so fast is that they have low wood density - their wood is relatively soft meaning it is fast to grow - and soft wood decomposes faster than hard wood so at first glance we would expect the dead wood in logged forests to decompose rapidly.

But it's not so clear cut. One of the most important animal groups in tropical rainforests are termites, many of which are specialist dead wood eaters, and the amount of wood these millions of small animals munch their way through is one of the key reasons why decomposition happens so fast. Termites have very soft bodies and don't respond well to logging. Logging removes a lot of the forest canopy, opening it up to the sun and making the forest floor a hotter and drier place. Because of that, logged forests only have about one third the number of termites that you find in untouched forest and that, in turn, means dead wood might decompose much slower.

This new research sets out to discover whether the high speed life and death of trees in logged forests counterbalances the loss of termites, or if one of these forces is stronger and outweighs the other. The answer is important. Protecting tropical forests is one of the most cost-effective ways for taking carbon dioxide out of the atmosphere. But by leaving behind large piles of dead wood, and potentially slowing the rate at which that dead wood decomposes, logging of those forests has the potential to render this key mechanism for combating climate change ineffective.

Planned Impact

The beneficiaries of this research fall into four broad groupings, the first three of which are interrelated and stand to gain similar benefits.

1. Public sector organisations, particularly the Sabah Forestry Department (SFD): SFD is responsible for the sustainable management of Sabah's extensive forest estate, issuing all logging concessions and permits for conversion of logged forest estates into plantation. PI Ewers works closely with SFD on the SAFE Project and SAFE has been strongly supported by Datuk Sam Mannan, the SFD Director. Ewers will be able to feed results and management recommendations to Datuk Mannan and the relevant management committees with the potential to directly influence SFD policies and requirements for new logging and land use clearance operations.

2. Private sector, specifically oil palm and forestry companies: This study is based at the SAFE Project, a collaboration between academia (led by PI Ewers) and the oil palm industry (particularly Sime Darby, the primary funder of SAFE). This research will help quantify the carbon balance of remnant forest patches that are retained within oil palm plantations - which have almost inevitably been logged - and has considerable relevance to the design of new plantations in which retaining High Carbon Stock forests is rapidly becoming an important consideration. Data collected in this project will also have relevance to designing best-practice Reduced Impact Logging techniques, and will be of interest to companies such as Usahawan Borneo, the logging company contracted to work at the SAFE Project. PI Ewers will be able to feed results to the Board of Sime Darby and to the CEO of Usahawan Borneo, along with any recommendations about best practice.

3. Third sector organisations, particularly conservation NGOs and industry groupings such as the Round Table for Sustainable Palm Oil (RSPO) and the High Carbon Stock (HCS) consortium: We will work closely with the South East Asia Rainforest Research Partnership (SEARRP) that supports scientific research in Sabah, including the SAFE Project, and that has two dedicated Impact Managers whose role is to translate science into policy. SEARRP holds a seat on the RSPO Biodiversity Committee and is well placed to feed results from this proposal into this high-level grouping of industry and conservation NGOs. Our results will have important implications for the definition of 'sustainable' landscapes and plantations that form a central component of oil palm certification schemes operated by RSPO and the scheme currently in development by HCS. PI Ewers is on the Science Advisory Committee for HCS and will be able to feed results directly into their decision making processes.

4. Academic community: The researcher community will benefit from the new knowledge and extensive datasets generated by the project and the scientific advancement on a topic of global importance. All data generated in our research will be made available via the NERC Environmental Information Data Centre and the SAFE Project online database. Our research is developing, calibrating and validating a new model of deadwood decomposition that will provide the academic community with a robust new tool that can be modified and used in other systems to simulate long-term dynamics of deadwood in response to climate and land use changes. Algorithms and code for the model will be made available as supplemental information in published papers.

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