Carbon Cycle

Well this is a fuzzy subject, but the forest is far more important than understood by the public in general. This post includes a recent editorial on the issue. Although much of what we do is a temporary altering of the human influence, it is beneficial to keep thinking about all of it. There is no question that using less fossil fuel to harvest timber or grow food is carbon positive, compared to conventional methods. That seems pretty simple. The values provided for the public good by proper forest management are yet to be quantified in a dollars and cents way. This understanding will further justify the cost of superior services, such as animal powered, low production, yet highly sensitive methods of man to age the forest. Look forward to the exchange.

SCIENCE: Old-growth forests found to be potent carbon storers (09/11/2008)
Christa Marshall, ClimateWire reporter

Old forests store more carbon than previously thought and should be considered in calculations of a country’s overall greenhouse gas output, according to a new study.

The finding challenges the long-held assumption that trees older than 150 years are “carbon-neutral” entities that neither spew nor absorb carbon dioxide into the air on average. After examining 519 old-growth forest plots worldwide, researchers found that they usually are “carbon sinks,” or natural storage containers with the potential to release large amounts of greenhouse gas back into the atmosphere if disturbed or burned.

“Many scientists today assume in their carbon models that old forests are carbon neutral. That needs to change,” said Beverly Law, a forest science professor at Oregon State University and one of eight co-authors of the research, published today in the journal Nature.

To reach their conclusions, the scientists measured carbon dioxide fluctuations at hundreds of spots, using chambers that measure gas output from soil. In some areas, they also took advantage of large towers operated by networks such as AmeriFlux that analyze carbon dioxide movements between land and the atmosphere.

The carbon-absorbing power of mature forests has been a hot topic of debate, with some arguing that climate change mitigation strategies should focus more on planting new trees, which can sap the greenhouse gas at high rates before they reach 100 years of age. Law noted, however, that it can take five to 20 years for immature forests to reach the point at which they absorb more carbon dioxide than they release.
A 1960s-era study is rejected

“In fact, young forests, rather than old-growth forests, are very often conspicuous sources of carbon dioxide,” the study’s authors wrote.

This is because decaying debris and soil that release greenhouse gases at a site often outweigh the carbon-vacuuming potential of very young trees, particularly if old trees have been cut down at the site or have been ravaged by fire or other natural phenomena, Law noted.

The study spotlights one of the flaws with the Kyoto Protocol, which assesses forestry threats to the climate based on whether widespread deforestation is imminent, said Laurie Wayburn, president of the Pacific Forest Trust. It also holds relevance, she said, for a potential cap-and-trade system in the United States and for the Western Climate Initiative, a multi-state collaboration which has been debating how to incorporate forests into a global warming strategy.

“We need to be giving credits for maintaining standing forests rather than just trying to protect the last stands,” she said. “That is a very different approach from current policy.”

Many mature forests also are not protected by international treaties, the study says, because of the false conclusion that they stop absorbing carbon after a certain period in their lifespan. That myth was derived from a 1960s-era analysis based on 10 years of data at one location, the study said.

Most old-growth trees sit on 30 percent of the world’s forest land mass, with half of that in the Northern Hemisphere.

Soil organic matter is a medium term carbon sink, that becomes long term if the soil is not disturbed causing the release of that carbon back into the atmosphere.

As a farmer, not a forester, I’m reminded of the theory of managed pulsed grazing, which has been shown to significantly increase soil organic matter. By harvesting top growth, causing root die back and decomposition without soil disturbance, soil microorganisms can effectively sequester significant amounts of the carbon in the roots into humus. By managing a pasture for maximum active growth, the maximum amount of atmostpheric co2 is absorbed and put into the soil.

Similarly, it seems that actively managing a forest stand for maximum active growth of the trees without disturbing the soil would have a similar impact. The report Jason posted indicated that young forest stands give off co2, because of the disturbed soil implicit in an even-aged young stand. In an uneven aged stand, managed to minimize soil disturbance, the ability to absorb carbon ought to be significant. Up until the management changes, that soil gets disturbed, and all that soil organic matter goes up into the atmosphere.

But no, not significant enough to offset the widespread burning of fossil fuels. There is no real way to do that.
-Tevis

@mstacy 2677 wrote:

… an old growth forest cannot sequester any net carbon. If vast quantities of carbon were somehow being pumped into the soil then old growth forest would be on some of the deepest and richest soils in the world. The reality is that these soils tend to be rather shallow. The rain forest is a great example. There’s a reason why swidden (slash and burn) agriculturists had to move so often. A few short years of cropping rapidly deplete the forest soils.

Ah, but take those old growth forests that are still left standing today for us to look at in context: they are still standing today. All of the forests on nice soil were cut down centuries ago, and a few times since. The base soil in the rainforests in light and prone to leaching, and the climate increases the leaching tendancy. Most old growth stands in north america are in mountainous, rocky or otherwise unfavorable terrain. Terrain that cropping would, as you say, deplete rapidly.
There is also a difference between old growth forest (in which growth has slowed due to the average age of the stand) and a managed, harvested, mature stand (with a higher percentage of young, actively growing trees).