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Science 29 June 1979:
Vol. 204. no. 4400, pp. 1380 - 1386
DOI: 10.1126/science.204.4400.1380
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Articles

Evergreen Coniferous Forests of the Pacific Northwest

R. H. Waring 1 and J. F. Franklin 2

1 Professor of forest ecology in the School of Forestry, Oregon State University, Corvallis 97331
2 Chief plant ecologist at the Forestry Sciences Laboratory, U.S. Department of Agriculture Forest Service, Corvallis, Oregon 97331

The massive, evergreen coniferous forests in the Pacific Northwest are unique among temperate forest regions of the world. The region's forests escaped decimation during Pleistocene glaciation; they are now dominated by a few broadly distributed and well-adapted conifers that grow to large size and great age. Large trees with evergreen needle- or scale-like leaves have distinct advantages under the current climatic regime. Photosynthesis and nutrient uptake and storage are possible during the relatively warm, wet fall and winter months. High evaporative demand during the warm, dry summer reduces photosynthesis. Deciduous hardwoods are repeatedly at a disadvantage in competing with conifers in the regional climate. Their photosynthesis is predominantly limited to the growing season when evaporative demand is high and water is often limiting. Most nutrients needed are also less available at this time. The large size attained by conifers provides a buffer against environmental stress (especially for nutrients and moisture). The long duration between destructive fires and storms permits conifers to outgrow hardwoods with more limited stature and life spans.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)