Liz Perkin's Masters Thesis

Relationship of Soil Nitrogen Availability to Riparian Tree Growth on the Queets River

Trees in riparian forests of the Pacific Northwest attain very large diameters

Project Summary

Large wood creates channel diversity and important habitat for salmonids (Oncorhynchus spp.). Generally, trees must be greater than 1 m in length and 0.1 m in diameter before they can play an effective geomorphic role. However, attaining a large diameter in a riparian zone altered by frequent channel movement requires rapid growth rates. The purpose of this study is to better understand the relationship between nitrogen availability (influenced by soil texture and depth, and rates of mineralization) and tree growth.

Bank undercutting recruits large wood to rivers

Objectives and Methods

This study will compare the growth rates of trees in permanent plots characterized by fine-textured soils and those characterized by coarse-textured soils. A second objective is to compare species composition of similar aged plots with fine- or coarse-textured soils. One of the subsidiary goals of this study is to determine if certain tree species are associated with soils with higher or lower levels of N mineralization. Plots of differing ages (20-400 yr) will be used, as soil depth and particle size, and N mineralization rates vary with stand age.

The work will take place on the Queets River, Olympic National Park, Washington, USA. Tree growth rates will be estimated by taking cores from the dominant trees in each plot, and analyzing the width of annual rings. Growth rates will be correlated with soil particle size and depth, and N mineralization.

Root wads add stability to log jams

Intellectual Merit

This study will contribute to the synthesis of biological and geomorphic knowledge of the Queets River assembled by Dr. Robert Naiman's lab group over the last 17 years. Although there were a few settlements in the Queets from 1890 to the 1950s, the Queets is still a very natural system. Protection of the Queets River has increased since the formation of Olympic National Park in 1938. Currently, approximately 98% of all rivers in the United States have had their flow modified in some way. The Queets is unique for a river its size in that it has never had its flow altered. As such, the Queets presents an often sought but rarely found entity in that it provides restoration teams and river managers with baseline data with which other, disturbed systems may be compared. A thorough understanding of a mostly undisturbed system will contribute greatly to the body of riparian knowledge. As one of the more natural rivers in the region, increased knowledge about soils and tree production in the Queets can inform management and restoration practices in coastal watersheds throughout the Pacific Northwest.

Broader Impact

This research will add critical information to a long-term ecological study of a relatively pristine area. The information gathered from this study will be combined with data collected over the past 17 yr on the Queets River to produce a broad document assessing the relationship linking riparian soils and vegetation, river processes, and fish habitat. The resultant document will not only aid in general scientific knowledge, but will be actively used by managers of undeveloped areas to determine proper riparian buffers and by city planners to improve degraded riparian areas for improved water quality and fish and wildlife habitat. This research will aid the expansion and improvement of the health of people in the Pacific Northwest, as well as improve their opportunties for recreation.

Photo credit: All photos by J.J. Latterell 2005