Catálogo de publicaciones - libros

Primary succession, the formation and change of ecological communities in locations initially lacking organisms or other biological materials, has been an important research focus for at least a century (Cowles 1899; Griggs 1933; Eggler 1941; Crocker and Major 1955; Eggler 1959; Miles and Walton 1993; Walker and del Moral 2003). At approximately 60 km, primary successional surfaces at Mount St. Helens occupy a minor proportion of the blast area, yet they are arguably the most compelling. The cataclysmic genesis of this landscape, its utter sterilization, and the drama of its reclamation by living organisms stimulate the imagination of scientists and nonscientists alike. These primary successional surfaces are the most intensively monitored areas at Mount St. Helens because of what they may teach us about the fundamental mechanisms governing the formation and function of biological communities. At a practical level, understanding successional processes provides a conceptual basis for the restoration of devastated landscapes (Bradshaw 1993; Franklin and MacMahon 2000; Walker and del Moral 2003).

Fish are important components of the Mount St. Helens aquatic system. Historically, no other region of Washington State supported as many native freshwater and anadromous species (anadromous fish mature in the ocean but spawn in freshwater) as did the region near Mount St. Helens (Table 12.1; McPhail 1967; McPhail and Lindsey 1986). Many of the anadromous species, including Pacific salmon ( spp.) and eulachon (), are keystone species that provide an important trophic link between aquatic and terrestrial ecological systems and are the foci of food webs that depend on marine-derived nutrients (Willson and Halupka 1995; Bilby et al. 1996; Levy 1997; Cederholm et al. 2001). In addition, fish are important consumers within rivers and lakes and can influence the species composition and structure of biological communities of these aquatic systems through herbivory, predation, and competition (Power 1990).

Volcanism is a major agent of natural disturbance in the Pacific Northwest and other regions of the world. Volcanic eruptions alter surrounding landscapes and ecosystems and strongly influence the distribution and abundance of species. Although ecologists documented responses of vegetation (del Moral and Grishin 1999; see Chapters 4 to 8, this volume), mammals (MacMahon et al. 1989; Crisafulli et al., Chapter 14, this volume), and arthropods (Edwards and Sugg, Chapter 9, this volume; Parmenter et al., Chapter 10, this volume) to volcanic disturbance, no equivalent work exists for amphibians. The 1980 eruption of Mount St. Helens created an opportunity to examine the initial responses of an amphibian assemblage to a diverse array of volcanic disturbances and to describe patterns of species colonization in areas that were influenced by the eruption. In addition, amphibian responses to the 1980 eruption may provide insights into how amphibians respond to major environmental changes over large spatial scales. This information is important because of the apparent declines of amphibian species during the past two to three decades (Blaustein and Wake 1990, 1995; Pechmann et al. 1991; Pechmann and Wilbur 1994; Sarkar 1996; Green 1997; Corn 2000).

The eruption of Mount St. Helens on May 18, 1980, and the subsequent activity of the volcano dramatically and significantly influenced the flora and fauna of the mountain and the surrounding area in a variety ofways.Many observers expected that no organism would survive the event anywhere close to the mountain and that it would take several decades for plants and animals to reestablish.

Mycorrhizae are symbioses between plants and fungi localized in the roots. These mutualisms represent important components in the recovery of vegetation because most plants depend on their fungal symbiont for a large portion of their soil resources, such as water, nutrients, and sometimes carbon. Although these organisms are generally rather cryptic and often unnoticed, they regulate many processes in ecosystems. The fungal hyphae, consisting of microscopic threads 2 to 10 μm in diameter, form the body of the fungus and ramify through the roots, forming a large surface area for exchanging nutrients and carbon. The hyphae then extend outward into the soil to provide nutrients and water to the host, become a sink for carbon, bind soil particles into soil aggregates, and produce sporocarps that are food for animals (Allen 1991; Smith and Read 1997; van der Heijden and Sanders 2002). External hyphae can be several meters to more than a kilometer per gram of soil. Thus, hyphae magnify the surface area of soil available for nutrient uptake and for soil-particle binding manifold compared with the roots alone.

The processes of decomposition and nutrient cycling of organic substances (plant leaf litter, woody stems, roots, and animal carcasses) are critical to the functioning of ecosystems (Swift et al. 1979; Cadisch and Giller 1997). The breakdown of dead plants and animals by scavenging animals, fungi, and bacteria is the first step in the recycling of important nutrients and is necessary for maintaining the productivity potential of soil (Lal et al. 1998; Stevenson and Cole 1999). In the case of the extremely disturbed forest ecosystem of Mount St. Helens, decomposition processes, acting on the plants and animals killed in the eruption, contributed to the early stages of soil building in landscapes covered in tephra. As plant and animal populations became reestablished after the eruption, individuals of these surviving and colonizing populations eventually died and decomposed, thereby contributing additional organic and nutrient resources to the soils. The development of soil organic fractions through decomposition in an otherwise mineral substrate (pumice and tephra) has undoubtedly facilitated the continued successional development of floral and faunal communities in the disturbed zones of the volcano and will certainly continue to do so in the future.

The pyroclastic flows of Mount St. Helens remain important to scientists seeking to understand the mechanisms of early succession. As in other primary-succession systems, biotic and abiotic development on these sites has been strongly influenced by legume colonists. Legumes are postulated to be critical contributors to nutrient pools during early succession, especially in infertile volcanic substrates, and are thought to facilitate colonization and growth of subsequent species that are limited by soil organic matter and by availability of critical nutrients such as nitrogen (Chapin et al. 1986; Franz 1986; Mooney et al. 1987; Vitousek et al. 1987; Chapin et al. 1994; Ritchie and Tilman 1995).

The 1980 eruption of Mount St. Helens devastated vast forestlands, triggered massive landslides and mudflows, and emplaced timber and volcanic debris in nearby lakes. Tephra and pyrolyzed forest debris rained down on dozens of subalpine, oligotrophic lakes scattered across a fan-shaped area affected by the lateral blast of the May eruption. This blast area, which encompasses the debris-avalanche, pyroclastic-flow, blowdown, and scorch zones, covers roughly 570 km north of the volcano. An additional, extensive zone northeast of the blast area received tephra fall.

The dramatic change and dynamic nature of recently disturbed landscapes often create major challenges for management of public safety and natural resources. This was certainly the case at Mount St. Helens following the 1980 eruption. The eruption triggered an immediate response that entailed search and rescue of missing people and protection of human health and property. Monitoring geological hazards and further volcanic activity was a key tool for providing warnings to the public and aided the State of Washington, USDA Forest Service, and other agencies in decisions regarding access, pending and current dangers, and area closures. As volcanic activity quieted and biotic and geomorphic change commenced, the perspectives of environmental scientists became pertinent to land- and water-management issues.

The sensational 1980 eruption of Mount St. Helens and the subsequent ecological responses are the most thoroughly studied volcanic eruption in theworld. The posteruption landscape was remarkable, and nearly a quarter century of study has provided a wealth of information and insight on a broad spectrum of ecological and physical responses to disturbance. The eruption and its effects on ecological and geophysical systems have many dimensions: a complex eruption affected an intricate landscape containing forests, meadows, lakes, and streams populated by diverse fauna and flora. This complexity created a rich environment and an exemplary living laboratory for study. Because the volcano is in close proximity to major metropolitan areas, scientists were able to perform reconnaissance trips and establish a network of permanent plots within days to months of the eruption. These early observations enabled scientists to assess the initial impacts of the eruption, which was important in understanding the subsequent quarter century of invasion and succession.