Soil Influence on Forest Vegetation Productivity and Patterns in the Eastern Cascades of Southern Oregon

Thesis (Master's)--University of Washington, 2016-06

Soils influence vegetation and can critically affect forest restoration results. Areas with similar parent materials can have changes in soil and vegetation across a slope, aspect, slope position, microtopography, and elevation. The objective of this project was to assess what soil characteristics influence vegetation productivity, patterns, and species. The study area for this project is located in the dry forests of the eastern slopes of the Cascade Mountains in the Fremont Winema National Forest of South Central Oregon and overlaps with a Forest Service NEPA project planning area called the Lobert Restoration project. Five major soil series, previously mapped by a collaborative effort between the USFS and NRCS, in the restoration study area were chosen to represent the variety of soil types in the NEPA project planning area. Within mapped areas of each of the soil series, four replicated sites were characterized for soil, vegetation, and landforms. Moisture loggers were placed to monitor soil water content. Soil moisture content throughout the year is a key factor of the productivity and patterns of the plant communities throughout the restoration area. Soil nitrogen and carbon in soil had little correlation with productivity or understory vegetation. Texture, rockiness of profile, buried horizons and slope position influenced vegetation by influencing soil moisture. Resource managers are challenged with the need to develop ecologically based treatment prescriptions that address all the various resource issues across large landscapes. Soil quality can be used as a tool to improve understanding and assessments for both land-use decisions and the sustainability of different land management practices