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Strategies to boost water yield must focus on the long term |  |
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| By: MIKE DOMBECK, Denver Post - 29 December 2002 | |||||||||
| Water has emerged as one of the most vexing environmental, social and political issues of the century. This observation became ever clearer to me in September at the World Summit on Sustainable Development in Johannesburg, South Africa, where water was a top issue. According to the United Nations, up to two-thirds of the world's people will face significant water shortages in the next 25 years, and major water conflicts will surely erupt. Here in the United States, water restrictions have become the norm, even in parts of the East where supplies once seemed inexhaustible. In the arid Southwest, tensions between the states and Mexico over the badly depleted Colorado River will worsen with time. Solutions are badly needed. Enter logging-for-water in Colorado's Rocky Mountains. Advocates tell us that clear-cutting 25-40 percent of high-country forests will increase water yields and ease regional water shortages. The idea is that cleared mountain slopes generate more runoff than intact forests, largely because less water escapes to the atmosphere and less soaks into the ground. In simple terms, it is a bit like the difference between a woodlot and a parking lot. While the idea sounds good at first, upon careful inspection it loses its appeal for several reasons. First, although research has shown that clear-cutting mountain slopes leads to higher water yields, it has also shown that intact, mature forests are most reliable at providing water over the long haul. How can science paint two very different pictures? The answer has to do, in large part, with the age of the forests being studied and the time periods over which water yields are measured. Young forests absorb more water for growth in the summer. That water then evaporates from the leaves. Young forests lose more snow directly to the atmosphere in the winter. When young forests are cut, water yields increase greatly. But as vegetation regenerates, the increases quickly disappear. Thus, to maintain high water yields through logging, forests must be cut and re-cut in a never-ending cycle. When stream flows over many years are compared, mature forests display relatively steady and high yields, whereas clear-cut forests display extreme highs and lows, with an overall lower long-term average than mature forests. Second, forests are partly responsible for the precipitation that falls on them - and on the land downwind. If we take away forests, nearby precipitation declines. The Fertile Crescent of ancient times, now the heart of arid Iraq, was once more humid and agriculturally productive than it is today. Now, it is anything but fertile or humid, due, in part, to centuries of environmental mismanagement that included the loss of the natural plant cover. Mature forests are an important link in the hydrologic cycle. It is no surprise then that two-thirds of the runoff in the United States flows from forests, which cover only a third of the land. The vegetation-precipitation feedback mechanism is real - and it should be maintained. Third, healthy forests not only produce the most water, but also the best water. The vegetation and plant litter on the soil surface keep water on the land longer, allowing more time for aquifer recharge versus surface runoff. As water percolates through soils, it is naturally filtered. Clear-cutting forests, regardless of how carefully it is done, results in higher peak flows following spring thaws and heavy rains. These higher flows lead to more erosion and higher sediment loads in streams. Healthy forests also are better at maintaining water chemistry and temperature. Clear-cuts lead to more nutrients in streams and higher summer water temperatures, not to mention chemical pollution associated with the herbicides that may be needed to keep deforested slopes clear. |
Wildlife, especially sensitive species like trout, suffers in these degraded habitats. Fourth, clear-cuts and the roads needed to access them impact geology and soils. Intact forests reduce mass movements of rock, soil and snow by stabilizing slopes. Although planners target areas with less risk, the chance of mass movement occurring is always higher where roads are built and the forest cover is removed. Landslides, avalanches and rockfalls can devastate surrounding landscapes. Even if mass movements do not occur, soils are adversely affected. The community of topsoil-building organisms is altered, nutrients become depleted, soil moisture drops, soil is compacted and erosion accelerates. Fifth, the direct costs of logging for water are high. The never-ending cycle of cutting, clearing and perhaps applying chemicals - again and again - is capital- and labor-intensive. The reservoirs needed to store the water from high-flow periods to augment the more extended low-flow periods are expensive to build and dredge. Dredging would also be needed in navigable streams and behind downstream hydro-electrical dams. Water purification costs would rise due to increased sedimentation. And costly cleanups would follow the floods and mass movements that would periodically arise. Finally, the historical mission of the national forests asks us to identify "the greatest good for the greatest number for the long run." A century ago, when the national forests were first designated, the idea was to provide a sustainable supply of timber and secure favorable conditions for water flows. This was in response to the "cut-and-run" era of timber harvests that left the United States with 80 million acres of denuded "cutovers," mostly in the East and Midwest. Huge post-logging slash fires, raging flash floods and soil erosion devastated the forests. Forest policy shifted to science-based forest restoration and management. If policies are shaped around forest health and watershed function, land managers will be able to arrive at the most equitable and sustainable management strategies. Given the growing demand for water, forest policy must consider long-term water quality and supply as an ever-increasing priority - perhaps a top priority in the spirit of "the greatest good." History tells us that when we try to manipulate nature for narrowly focused outcomes, we are often surprised by the unintended consequences. Our efforts to manipulate the Florida Everglades and to dam rivers in the Pacific Northwest serve as poignant examples. Few would have predicted the high social, economic and environmental costs that we struggle with today because we built canals, levees and dams in the name of development. With these realities in mind, forest management should be geared to the long haul. Yes, fuel reduction to protect communities in high-risk, fire-prone areas should be done, and yes, the wood harvested should be used to meet our ever-growing needs. But this does not mean that we should clear-cut millions of acres - and we certainly should not do so under the guise of water production. We continually seek more from the land than it can sustainably provide. I would hope that as the Bush administration takes up new forest-planning regulations and Colorado policymakers consider the fate of the Rocky Mountain forests, water quality and long-term supply become the foremost performance measures. The seductively simple logging-for-water concept should be abandoned. |
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