The Giving Trees

For some people forests are measured in board-feet of lumber. For others they're a source of spiritual renewal. But scientists are finding that protecting ancient trees could also be an important new strategy in the fight against global warming.

I climb a long series of ladders that lead to nothing but sky. Wind hums in the struts of the metal tower around me, causing it to vibrate like a giant guitar string and carrying the scent of warm pinesap, which saturates the air of Oregon's East Cascades in late summer. As I move higher, I pass arrays of high-tech gear that swallow samples of air, then analyze the amount of carbon dioxide in each gulp.

Just behind me, her long, gray-shot hair whipping in the wind, Beverly Law steps onto the tower's topmost platform, 120 feet aboveground. Law, a professor of global forest science at Oregon State University, uses towers like this one, with their whirring gizmos, to track the forest's vital signs and reveal the complex relationship between trees and atmospheric carbon. She is the director of the AmeriFlux Network, an international collaborative project founded in 1996 that tracks the exchange of CO2, water vapor, and energy in all sorts of biomes throughout the Americas, from the Alaskan tundra to the Amazon rainforest. Her work, and that of the network, challenges conventional wisdom about how forests help to mitigate global warming.

In an era of climate crisis -- perfectly symbolized in the dwindling snowpack on the peaks of the Three Sisters, off to our southwest -- a clearer understanding of the role forests play in absorbing carbon is becoming crucial. Mass deforestation, particularly in tropical countries such as Brazil and Indonesia, accounts for more than 20 percent of annual greenhouse gas emissions. Meanwhile, recent studies show that Northern Hemisphere forests, now beginning to bulk up as they recover from centuries of logging, capture large amounts of CO2 from the atmosphere. Finding ways to preserve forests-wherever they may be-can buy us precious time to wean ourselves from fossil fuels.

I've spent much of my life surrounded by argument and anger over the fate of forests. For more than a decade I walked the woods as a wildlife biologist, learning to see them through the eyes of spotted owls, salamanders, tree voles-and landowners. My husband, a professional forester for the California Department of Forestry, spent several difficult years working to enforce state environmental regulations governing commercial timberland, taking flak from both loggers and eco-protestors. The people I've met along the way have always valued forests intensely, though often for very different reasons: as a renewable source of lumber and jobs, a haven for endangered wildlife, a source of clean water, a place of spiritual renewal. Now we all need to take a fresh look at how we judge the worth of our forests. The capture of CO2, an invisible gas, may be just as vital as an owl or a marten moving through the trees, as necessary as the shelters we build out of solid wood.

Plants take in CO2 and harness the energy of the sun to drive the chemical reaction that melds carbon with water, producing the substance of stem and leaf and releasing oxygen. When darkness or drought bring this process of photosynthesis to a halt, plants respire, just as humans do. That is, plants breathe in oxygen and exhale CO2. But over the long life span of trees in an undisturbed forest, huge reservoirs of carbon are stored for great stretches of time in the organic matter in soil as well as in living wood.

People who cut down trees for a living tend to measure their value in dollars and cents. Traditionally, the timber industry has seen mature forests, with massive trees left standing and big logs rotting on the ground, as examples of waste; replanted clear-cuts, by contrast, represent an ideal of economic productivity. Now global warming has forced foresters to address the impact of logging on the flow of carbon between forests and the atmosphere, and many in the industry have insisted that stands of young, fast-growing trees capture carbon more efficiently than do older forests. Using a recently developed technology called the eddy covariance method-more commonly known as eddy flux measurement-Bev Law and her colleagues are showing that those assumptions are wrong.

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