Forest loss a climate threat

When people think about global warming and climate change, we usually think about emissions from cars, factories, and power plants. But the changes that we have wrought on the forested landscape have also had a major effect on our climate.

In California since 1700 we have converted approximately 40% of our native forestland to other uses through urbanization and agricultural conversion. This is hardly surprising, when you think of all the cities, towns and agriculture located in formerly forested areas. Even now, however, while we understand the impacts to climate change (not to mention habitat loss), California continues to lose forest land at an alarming rate.

According to the California Department of Forestry and Fire Protection (CDF), each year between 1989 and 2000, nearly 70,000 acres received some level of development. Of that total, nearly 28,000 acres per year was divided into relatively small lots, with at least one house per 20 acres. CDF estimates that between 2000 and 2020 California will lose nearly 5% of its forested area to other non-forest uses.

The reason for these conversions is primarily economic these forestlands are oftentimes more valuable financially as real estate than for timber production, and landowners are predictably seeking to maximize economic return. Estate taxes provide another perverse incentive to sell off forestland for development.

The issue of how to preserve our remaining forestland, and increase our capacity for carbon sequestration in trees, has moved to the forefront because the state anticipates achieving 20% of the carbon reductions required by AB 32 through forest activities. Although the details are very much still under development, four general approaches have been identified: reforestation, improved forest management, fuels reduction, and urban forestry.

To meet the goals established by the Global Warming Solutions Act, the state Air Resources Board wants forests to capture an additional 16 million tons of carbon dioxide annually by 2020. Since trees planted this year will still be young saplings in 2020, the carbon ultimately sequestered by reforestation efforts will increase more substantially in the future assuming that the trees are left to grow. This is important because although reforestation efforts may seem like a relatively expensive way to capture carbon when viewed over the next 10 - 15 years, it becomes much more cost-effective over the course of the next century.

Trees are a very efficient way to capture and store carbon approximately half of the weight of a tree is carbon. A large portion of this carbon, however, is lost and released during logging. In a typical California forest, approximately 2/3 of the carbon is above ground, with the remainder in roots and soil. Roughly 60% of the volume of the forest makes it to the mill (branches and slash are generally left in the forest). Then there is some level of inefficiency at the mill when the trees are turned into lumber. All told, only 25 - 50% of the carbon in a forest ends up in lumber, probably closer to 1/3. The destiny of that lumber then becomes critical if it is used to build a house it will stay sequestered for some time, whereas other uses such as pallets would have a much shorter lifespan before the carbon is re-released into the atmosphere.

There are a whole host of issues to address as the focus on forests turns toward their contribution to carbon sequestration. It will be important to remember that forests have many other values such as habitat and water quality. And we'll need to be realistic and proactive in how we manage forests to make sure that the hotter, drier California of the future continues to have amazing forests.

Paul Mason, legislative rep, Sierra Club California