climate change

By John A. Helms. Ph.D. -

THE REPORT released recently by I California Governor Arnold Schwarzenegger's Climate Action Team identifies the forest resource sector as one of the most significant strategies to reduce emissions. That's good news. It's high time California encouraged the judicious use and management of its forestlands.

While burning fossil fuels spervs carbon and other greenhouse gases into the atmosphere. forest management can reduce carbon pollution. It can also buy us time to develop more efficient technologies that ultimately minimize human contributions to global warming.

In particular, it's the young trees and forests that are most efficient in taking up carbon. Not that old forests don't help-they do. But when their capacity to remove carbon is measured against young forests, old forests come up short.

First, a little Biology l0l: Trees take up carbon dioxide from the air and release oxygen in the process of photosynthesis. The carbon is stored in leaves, branches, stems, roots and soil. Trees also respire some carbon dioxide back to the atmosphere. In young forests. the uptake of carbon dioxide greatly exceeds the loss due to respiration. The reverse can be true for very old forests.

This prompts two questions: Can rve enhance a forest's capacity to store. or sequester, carbon? And if so. rvhat's the best rvay to do it?

The first answer is fairly straightforrvard. Increasing carbon storage in forests goes hand-in-hand rvith other forest management _qoals. such as providing essential tvood products. enhancing rvatershed health. and maintaining biodiversity across the landscape. What's -eood for forest health is good for carbon sequestration. Forest management can certainly increase carbon sequestration. especially rvhen the carbon forests capture is stored long-term in rvood products like lumber for building construction and furniture.

So horv do rve enhance carbon sequestration by forests? By improving grorving conditions. controllin-s stand density. increasin_e tree vigor. examining rotation lengths. and encouraging the development of urban forests. The more rapidly leaves are produced, the more carbon is taken out of the atmosphere. The faster a tree grows. the more effective it is at removing carbon from the air. Creating ideal conditions for growing trees also creates ideal opportunities for carbon sequestration.

As forests become older the rate at rvhich they take up carbon slows and the rate at rvhich they lose carbon to the atmosphere through respiration and decomposition accelerates. Though older forests rvith many large trees may store more carbon than young forests. there is a trade off in that young forests are better at sequestering carbon.

The climate-helping characrer of young forests should be a boon to society because rvhether you're interested in rvood production or carbon sequestration, the forest-management approaches are similar: you want to increase leaf area. maintain forest health. and accelerate grorvth. That means thinning forests to remove the less vigorous trees. leaving the rapidly grorving trees.

Replanting the land rvirh fast-grorving trees quickly restores the forest canopy and continues the process of sequestering carbon.

The same forest-management techniques that maintain healthy foresrs and sequester carbon offer another climate-change benefit: they reduce the threat of high-intensity rvildfires that release tremendous amounts of carbon into the air in a single. catastrophic event.

Although there's currently no market incentive in place to manage forestland to store carbon. California established the Climate Action Registry in 2001 and is refining prorocols that may eventually rervard forest management activities that increase carbon sequestration. Without financial incentives it is unlikely that forests rvill reach their full carbon sequestration potential.

But this much is certain: rapidly -erorving trees sequester carbon more quickly and efficiently than old ones. That fact should stay front and center in policy discussions. If rve rvant to maximize carbon sequestration and stora_se. rve need forest management that results in healthy forests of all ages on the landscape. That means sustainable forestry. and plenty of young forests.