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Abstract

Project Mentor(s): Mary Poulson, PhD

Water availability and coniferous tree species can cause acidification and a change in soil fertility. Previous research in European forests found that rainfall, soil acidity, and conifer prevalence influenced soil quality and biodiversity. However, not much is known about these effects in the Pacific Northwest’s forests. Three forests were chosen based on a gradient of annual precipitation. The Hoh Rain Forest, the Tiger Mountain State Forest, and the Okanogan-Wenatchee National Forest were used for wet, mesic, and dry conditions, respectively. Each location had a three-by-six grid spaced 50 meters between each plot. The location was marked, and a six-inch hole was dug at the base of the nearest tree to collect a soil sample. Collected soil samples were tested for pH, water content, and nutrient content. Soil pH ranged from 5.5 at Okanogan-Wenatchee National Forest, 6.0 at Tiger Mountain State Forest, and 6.5 at the Hoh Rain Forest. Douglas-fir, ponderosa pine, western red cedar, bigleaf maple, and red alder were grown in the CWU Biology Greenhouse. Trees were grown in simulated soil moisture regimes to those of the chosen sites. Results of this study indicate that the occurrence of coniferous tree species, particularly ponderosa pine, and increased soil water content will contribute to soil acidification. This study provides insight into the environmental interactions occurring in Washington’s forests and will allow for better forest management practices.

SOURCE Form ID

176

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