Liz Perkin's Masters Thesis

Relationship of Soil Water Holding Capacity and Nitrogen Availability to Riparian Tree Growth on the Queets River, WA

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

Project Motivation

Large wood creates channel diversity and important habitat for salmonids fishes. 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 soil water holding capacity and nitrogen availability (influenced by soil texture and depth, and rates of mineralization) and tree growth in a riparian area of the Pacific Coastal Ecoregion.

Bank undercutting recruits large wood to rivers

Objectives and Methods

This study compared the growth rates of trees in permanent plots characterized by fine-textured soils and those characterized by coarse-textured soils. Plots of differing ages (20-400 yr) were used, as soil depth and particle size, and N mineralization rates vary with stand age.

The work took place on the Queets River, Olympic National Park, Washington, USA. Tree growth rates were 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 water holding capacity, 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.

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