Keystone Herbivores and Their Impact on Vegetation and Successional Dynamics within the Debris Avalanche Deposit at Mount St. Helens National Volcanic Monument

Abstract

The debris avalanche at Mount St. Helens National Volcanic Monument has provided researchers with an important template in which to study various geological and ecological processess. This thesis describes the impact of two keystone herbivores on vegetation and successional dynamics within a small portion of the debris avalanche ecosystem. Chapter 1 addresses important background information pertinent to herbivory, disturbance ecology, and successional dynamics. Chapter 2 describes the role of elk (Cervus elaphus roosevelti) herbivory within a plant community and the subsequent changes in assemblage composition from 1992 to 1999. Finally, Chapter 3 concerns the relationship between sitka willow (Salix sitchensis) morphology and infestation of the exotic weevil, the willow stem borer (Cryptorhynchus lapathi).