The Union of Concerned Scientists on CLEARCUTTING and C02 Sequestering

The world’s forests provide many important benefits: Home to more than half of all species living on land, forests also help slow global warming by storing and sequestering carbon. Forests are sources of wood products. They help regulate local and regional rainfall. And forests are crucial sources of food, medicine, clean drinking water, and immense recreational, aesthetic, and spiritual benefits for millions of people.

As globally important storehouses of carbon, forests play a critical role in influencing the Earth’s climate. Forest plants and soils drive the global carbon cycle by sequestering carbon dioxide through photosynthesis and releasing it through respiration. Although carbon uptake by photosynthesis eventually declines as trees age, many mature forests continue to sequester carbon in their soils.

Yet, in many parts of the world, forests are being rapidly cleared for agriculture or pasture, destructively logged and mined, and degraded by human-set fires. When forests are degraded or cleared, their stored carbon is released back to the atmosphere during harvest and through respiration, thus these forests are net contributors of carbon to the atmosphere.

When forests are burned, cleared, or otherwise degraded, their stored carbon is released into the atmosphere. The forests of the Pacific Northwest and Southeast could double their storage of carbon if timber managers lengthened the time between harvests and allowed older trees to remain standing.

Tree Plantations
Clearing mature forests and replacing them with fast-growing younger trees is not a solution. To be sure, younger trees draw carbon out of the atmosphere more quickly. But cutting down mature forests releases large quantities of CO2. And replacing natural forests with tree plantations destroys biodiversity—the web of life that supports and nourishes all plants and animals.

Forest-based mitigation of global warming can occur by three strategies:
• Conservation of existing forests - to avoid emissions associated with forest degradation or clearing.
• Sequestration by increasing forest carbon absorption capacity - occurring primarily by planting trees or facilitating the natural regeneration of forests, especially on marginal land and by making changes in forest management to increase biomass.
• Substitution of sustainably produced biological products - substituting wood products for materials requiring energy-intensive production, such as aluminum or concrete, and sub- stituting woody biomass for fossil fuels as an energy source.

UCS generally supports the use of market-based approaches to promote forest-based climate mitigation options, provided that they achieve the following:

1. Ensure real, verifiable, and lasting greenhouse gas reductions by designing policies that account for the potential reversibility of forest-based emissions reductions. For example, a change in land management or a natural disturbance can re-release carbon stored under a forest-based program to the atmosphere.

2. Create incentives for activities that are environmentally and socially beneficial. Natural forests must not be cleared in preference for plantations, for example, nor should historical fire regimes be altered to promote biomass accumulation. Policies to conserve or enhance forests for carbon storage must also consider other benefits that forests provide. In general, managing forests for carbon conservation by increasing forest area, forest age, and tree size can have beneficial effects on biodiversity and forest ecosystem function.

CLEARING FORESTS and PLANTATIONS
There is a widespread and misguided belief that logging or clearing mature forests and replacing them with fast-growing younger trees will benefit the climate by sequestering atmospheric CO2. While younger trees grow and sequester carbon quickly, the fate of stored carbon when mature forests are logged must also be considered. When a forest is logged, some of its carbon may be stored for years or decades in wood products. But large quantities of CO2 are also released to the atmosphere - immediately through the disturbance of forest soils, and over time through the decomposition of leaves, branches, and other detritus of timber production. One study found that even when storage of carbon in timber products is considered, the conversion of 5 million hectares of mature forest to plantations in the Pacific Northwest over the last 100 years resulted in a net increase of over 1.5 billion tons of carbon to the atmosphere.