The eruption of Mount St Helens on 18 May 1980 transformed more than 600 km² of green coniferous forests and clear cold lakes and streams of the Cascade Mountains to a gray ash- and pumice-covered landscape. Although other volcanic eruptions have had more important ecological and human consequences, the 1980 eruption of Mount St Helens and the ensuing ecological responses are the most thoroughly studied in the world. This may be explained by the close proximity of the volcano to major metropolitan areas, allowing scientists to perform reconnaissance trips and establish permanent plots within a few days of the eruption.

This book synthesizes the ecological research that has been conducted in the 25 years since the eruption by hundreds of scientists, students, and technicians. The fields of research are very broad, ranging from geology to plant and animal ecology of both terrestrial and aquatic systems. The 20 chapters, in 5 sections, provide detailed results of experiments and observations of 25 years of evolution of the physical environment (Section 1, Chapters 1–3), plant communities (Section 2, Chapters 4–8), animal communities (Section 3, Chapters 9–14), and ecosystem processes (Section 4, Chapters 15–18). The last section (Chapters 18–20) highlights 11 important lessons learned from these 25 years of research experience.

Following an introduction, the first section provides information on the pre-eruption physical and ecological conditions and the main physical and environmental events from March 1980 to late 2004. The chapter on the pre-eruption conditions is very useful for non-specialists, although the information provided is certainly too general for specialists. In particular, the climatic presentation of the area is rather simple, with no emphasis on spatial variability and an increasing rain shadow to the east of the volcano. The following chapter precisely defines 6 zones of decreasing disturbance intensity with increasing distance from the volcano: (i) the Pyroclastic Flow Zone, (ii) the Debris Avalanche Zone, (iii) the Mudflow Zone, (iv) the Blowdown Zone, (v) the Scorched Zone, (vi) the Tephra Fall zone. These zones are used by all specialists as a basis for designing their experiments or observations.

Chapters 4 to 6 present the results of long-term experiments conducted on the survival and establishment of plant communities in the Tephra Fall, Debris-Avalanche and Mudflow zones, respectively. In the less impacted Tephra Fall Zone, the authors emphasize the roles of species traits and snow cover at the time of the eruption whereas, in the 2 latter highly disturbed zones, the authors underline the importance of the dispersal filter to understand community succession, as well as the occurrence of subsequent disturbances. In Chapter 7, focusing on early vegetation development in several highly disturbed zones, the authors recognize the importance of chance events and highlight the unpredictability of the course of succession at these early stages. The last chapter of this second section, a remote sensing approach to the whole area, emphasizes the importance of either environmental factors or of the distance to surviving individuals, depending on the severity of the disturbance.

Chapters 9 and 10 focus on arthropod communities, Chapter 11 on herbivory on prairie lupine (an important colonizer of the highly disturbed zones), Chapters 12 and 13 on aquatic animals (fish and amphibians, respectively) and Chapter 14 on small mammals. In general, the authors emphasize the importance of life-history traits for species survival and the surprisingly rapid colonization of animal communities—particularly aquatic organisms—as compared to plant communities. For example, 20 years after the eruption, fish assemblages were almost similar to those commonly occurring in other parts of the Cascades.

The fourth section deals with ecosystem processes and, in particular, mycorrhizae (Chapter 15), patterns of decomposition (Chapter 16), legume effects (Chapter 17), and response and recovery of lakes. Mycorrhizal responses in terrestrial ecosystems and microbial responses in lakes appeared to be extremely fast with a recovery of almost all ecosystem characteristics in most lakes by 1986, although geothermal activities impede a return to the initial conditions. A decomposition study of rodent carcasses elegantly demonstrates that decomposition was inversely correlated to disturbance intensity, although the authors emphasize that a confounding effect of elevation is likely, because the most disturbed sites occur at a much higher elevation than the least disturbed ones. In contrast to the conclusions of the other sections, chance and dispersal effects do not seem to affect ecosystem processes which are more directly driven by site quality and thus disturbance intensity.

In the last section, after a chapter focusing on ecological perspectives on management of the Mount St Helens landscape, the authors emphasize the difficulty of integrating all the information provided from these 25 years of research. They agree on the absence of a unified theory from which to evaluate the ecological responses to the 1980 eruption, preferring to summarize the story of the aftermath of the eruption of Mount St Helens in terms of 11 lessons provided by this research. Key among these are the importance of the biotic and abiotic legacies which acted as nuclei for species recolonization, the rapidity of some ecological responses, and their high variability and spatial heterogeneity. Another important conclusion of the authors concerns the unpredictability and complexity of successional processes: “All described processes of successional theory have been shown to occur on Mount St Helens and sometimes concomitantly at one location, which underscores the limits of any one existing mechanistic model to explain succession.” In summary, this book offers an unprecedented look at the complex interactions of biological and physical systems in response to a major volcanic disturbance.