Although the burning of fossil fuels has been responsible for the majority of humanity's carbon emissions, land use changes are thought to have been responsible for nearly 20 percent of the CO 2 that we've put in the atmosphere. Most of this has involved the clearing of forests and grasslands for agriculture, and many efforts to sequester carbon involve blocking or reversing these processes through the preservation of forests or planting of new trees.

But the fate of the material cleared during deforestation isn't a simple one. Some of it ends up being burned in the process of clearing. Other wood products wind up in relatively permanent structures, keeping their carbon out of the atmosphere for decades or more. A new study has looked at the fate of cleared woodlands on a country-by-country basis and found that the rates of sequestration can range from 62 percent down to essentially nothing.

The fate of forests varies widely across the globe. In many areas of the tropics, woodlands are burned to clear land for agricultural uses simply because it's the most convenient thing to do. In others, the wood is harvested and either burned directly or converted into charcoal, acting as a form of biomass energy.

In other cases, the harvested wood is converted into products with varying degrees of permanence. Some portion of the trees can't be used to produce products, and ends up dumped back into the carbon cycle immediately. Another fraction gets converted into things like paper, which, even after recycling, has a finite lifespan before it gets burned or put into a landfill. Finally, some of the tree is converted into lumber or other semi-permanent materials like fiberboard or plywood.

Depending on the precise use of the material, the harvesting of forest can either release carbon into the atmosphere immediately or sequester it for long enough that it could have implications for carbon management policies. The new study provides a potentially useful view of the impact of deforestation by examining the different fates of wood in different countries.

Although the analysis was undoubtedly complex, the take-home message is simple: the clearing of forests in Europe and North America means a very different thing from what it means just about anywhere else. In the tropics and the portions of Asia that aren't Russia (accounting for about three-quarters of the world's nations), the majority of wood is either used for fuel, converted into paper, or simply not used because it has no commercial value. In these cases, by thirty years after harvesting, less than 15 percent of the carbon is still sequestered in lumber or landfills. For most of them, that number is somewhere around zero.

In contrast, a lot of the timber in the US, Europe, and Russia appears to have commercial value, and a large fraction of that can be converted into lumber or wood panels. As a result, even 30 years in, somewhere between 15 percent and half of that carbon is still stored. Even out to 100 years, the fraction sequestered can be as high as 30 percent. Overall, this leads to a fairly radical imbalance: "The median carbon stored after 30 years is 2 percent for rest of world and 36 percent for Europe, the United States, and Canada."

The authors looked at a few countries to get a sense of what happens to trees in both of these types of nations. In Germany, a bit over a quarter of it is burned immediately, and another 17 percent is burned as fuel. Twenty-eight percent is made into paper, and ends up in a landfill. Because paper can be broken down relatively easily, this ends up putting carbon back into the atmosphere. Another quarter ends up either as lumber or processed wood products, both of which drive long-term storage of carbon. Germany was contrasted with Indonesia, where 92 percent of the forest cleared doesn't go into any sort of usable product.

The study has some limits that the authors highlight in their discussion. The biggest is that one of the primary outputs of landfilled biomaterials is methane, which has a much higher greenhouse potential than carbon dioxide (the fate of material that's burned). So, in the US and Europe, the positive impact of the higher sequestration might be partly offset by the fact that these nations landfill a lot of the other wood products. The other key issue is the fate of the land after deforestation. If it's immediately replanted with trees, then the harvesting should be relatively carbon neutral, even if all the wood is used as fuel (disruptions of the soil ecosystem being the largest complication here).

Although there's still some work to do, the paper makes a nice end-piece with our recent coverage of wood as a modern building material. Those wood products—treated, laminated, and heavily processed—might expand the number of forest products that are considered commercially viable. And, if we're to manage forestry for carbon sequestration, developing ways to get these processing techniques to be viable in the tropics could go a long way toward making their trends look closer to the ones seen in Germany.

Nature Climate Change, 2012. DOI: 10.1038/nclimate1535 (About DOIs).