This project began in 1980 following the eruption of Mt. St. Helens in Washington and will become one of the longest continuous study of vegetation recovery after a profound disturbance. The basic method is to repeat sampling of permanent plots on sites with different histories and geographic contexts. It seeks to develop an understanding of ecological community assembly (primary succession). Experimental removal of key species will test hypotheses and a study of wetland development will provide dramatic comparisons to documented succession in uplands. The role of the nitrogen-fixing lupines in redirecting, accelerating or retarding succession is a focus of the current study. This project will explore how competition, landscape factors, chance and local heterogeneity affect later stages of primary succession and under what conditions vegetation becomes more predictable. Understanding the constraints to vegetation development on volcanic substrates will permit more effective vegetation restoration on mine tailings and quarries. Understanding dispersal limits, establishment processes and the balance between competition and facilitation will all improve vegetation management. The project will train several graduate and undergraduate students. The data are being made available on the Andrews Long Term Ecological Research web site, and can be used to further education, as a basis for theoretical studies, and to compare other damaged systems.
The completion of this grant marked the termination of 31 years of research describing early recovery patterns of vegetation on Mount St. Helens. This project resulted in over 70 publications directly or indirectly related to this research. Permanent plots formed the basis of this study, large-scale landscape surveys were also fundamental to satisfying the questions posed. The data collected since 1980 are being mined to develop a general book on succession at Mount St. Helens. During this grant period, numerous accomplishments led to highlighting many lessons concerning primary succession. Chief among these are: 1. Succession rates are related to environmental stress, with infertile sites or those at high elevation developing more slowly than fertile or lower elevation sites. These rates are generally slowing down. 2. Deterministic control of vegetation development is weak. Species assembly is subject to several stochastic factors, so succession trajectories may proceed in several directions, even from within one habitat. 3. Due to priority effects, historical events and the vagaries of dispersal, initial species composition in similar sites may be different; because deterministic factors (e.g. competition) are weak, sites rarely converges to vegetation of similar composition. 4. Deterministic assembly rules have yet to be found. General, weak rules exist, but none can be used to predict species composition. 5. Small depressions (potholes) were studied since 1992, and latest studies demonstrated that deterministic factors (e.g. competition, moisture) are becoming more important. Vegetation converged to a limited degree, but individual potholes retain their individuality. 6. Other studies, at different scales, found increasing deterministic control of vegetation, but much variation remains unexplained by measured variables. There is a fundamental limit to the strength of links between vegetation and environment that allows alternative trajectories to develop from similar initial conditions.
