Charles M. Crisafulli

The forgotten stage of forest succession: early‐successional ecosystems on forest sites

Early-successional forest ecosystems that develop after stand-replacing or partial disturbances are diverse in species, processes, and structure. Post-disturbance ecosystems are also often rich in biological legacies, including surviving organisms and organically derived structures, such as woody debris. These legacies and post-disturbance plant communities provide resources that attract and sustain high species diversity, including numerous early-successional obligates, such as certain woodpeckers and arthropods. Early succession is the only period when tree canopies do not dominate the forest site, and so this stage can be characterized by high productivity of plant species (including herbs and shrubs), complex food webs, large nutrient fluxes, and high structural and spatial complexity. Different disturbances contrast markedly in terms of biological legacies, and this will influence the resultant physical and biological conditions, thus affecting successional pathways. Management activities, such as post-disturbance logging and dense tree planting, can reduce the richness within and the duration of early-successional ecosystems. Where maintenance of biodiversity is an objective, the importance and value of these natural early-successional ecosystems are underappreciated.

Ecological responses to the 1980 eruption of Mount St. Helens

Disturbance, Survival, and Succession: Understanding Ecological Responses to the 1980 Eruption of Mount St. Helens.- Geological and Ecological Settings of Mount St. Helens Before May 18, 1980.- Physical Events, Environments, and Geological-Ecological Interactions at Mount St. Helens: March 1980-2004.- Survival and Establishment of Plant Communities.- Plant Responses in Forests of the Tephra-Fall Zone.- Plant Succession on the Mount St. Helens Debris-Avalanche Deposit.- Geomorphic Change and Vegetation Development on the Muddy River Mudflow Deposit.- Proximity, Microsites, and Biotic Interactions During Early Succession.- Remote Sensing of Vegetation Responses During the First 20 Years Following the 1980 Eruption of Mount St. Helens: A Spatially and Temporally Stratified Analysis.- Survival and Establishment of Animal Communities.- Arthropods as Pioneers in the Regeneration of Life on the Pyroclastic-Flow Deposits of Mount St. Helens.- Posteruption Arthropod Succession on the Mount St. Helens Volcano: The Ground-Dwelling Beetle Fauna (Coleoptera).- Causes and Consequences of Herbivory on Prairie Lupine (Lupinus lepidus) in Early Primary Succession.- Responses of Fish to the 1980 Eruption of Mount St. Helens.- Amphibian Responses to the 1980 Eruption of Mount St. Helens.- Small-Mammal Survival and Colonization on the Mount St. Helens Volcano: 1980-2002.- Responses of Ecosystem Processes.- Mycorrhizae and Mount St. Helens:Story of a Symbiosis.- Patterns of Decomposition and Nutrient Cycling Across a Volcanic Disturbance Gradient: A Case Study Using Rodent Carcasses.- Lupine Effects on Soil Development and Function During Early Primary Succession at Mount St. Helens.- Response and Recovery of Lakes.- Lessons Learned.- Ecological Perspectives on Management of the Mount St. Helens Landscape.- Overview of Ecological Responses to the Eruption of Mount St. Helens: 1980-2005.

Causes and Consequences of Herbivory on Prairie Lupine (Lupinus lepidus) in Early Primary Succession

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 km2, primary successional surfaces at Mount St. Helens occupy a minor proportion of the blast zone, 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). Succession is a fundamentally multitrophic process. It involves not only plants but also herbivores, predators, and decomposers. Yet, the important effects of these other trophic levels are sometimes ignored. Study of trophic interactions (i.e., interactions between consumers and resources) in primary succession can provide new insights into mechanisms of primary succession and can inform the debates surrounding what controls the level of herbivory in terrestrial ecosystems. In this chapter, we describe often-devastating attacks by insect herbivores on the prairie lupine, Lupinus lepidus var. lobbii (Dougl.), and how they have affected the (spatial) spread of this little plant, generally considered the most important colonist during the first two decades of primary succession on the Mount St. Helens Pumice Plain. We also discuss a surprising spatial pattern in the intensity of lupine herbivory on the Pumice Plain and outline two hypotheses for this pattern. One hypothesis is based on gradients in plant quality; the other is based on gradients in the density and diversity of the herbivores’ natural enemies. Both hypotheses involve processes that are inherent to primary succession and that are likely relevant to systems beyond Mount St. Helens.

Overview of Ecological Responses to the Eruption of Mount St. Helens: 1980–2005

The sensational 1980 eruption ofMount St.Helens and the subsequent ecological responses are the most thoroughly studied volcanic eruption in theworld. The posteruption landscapewas remarkable, and nearly a quarter century of study has provided awealth 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. Suddenly, and almost beyond comprehension, at 8:32 a.m. on May 18, 1980, and lasting for little more than 12 hours, the eruption of Mount St. Helens transformed more than 600 km2 of lush, green forest and meadows and clear, cold lakes and streams to a stark gray, ashand pumice-covered landscape (see Figure 1.1; Swanson et al., Chapter 2, this volume; Swanson and Major, Chapter 3, this volume). The area influenced by the eruptive events will respond to them for hundreds or even thousands of years. However, even within the 24 years since the eruption, substantial change took place as hill slopes gradually turned from gray to green, opaque lakes cleared, and streams flushed sediment from their channels. Some of the initial ecological responses are well advanced; others have been set back by secondary disturbances; and yet others, such as soil development, will respond to the eruption over millennia. The major 1980 eruption created distinctive disturbance zones that differed in the types and magnitudes of impacts on terrestrial and aquatic systems, including the types and amounts of surviving organisms and other legacies of the preeruption ecological systems (Figure 20.1). Thereafter, the natural system consisting of surviving and colonizing plants, fungi, animals, andmicrobes began responding to the new conditions. During the subsequent decades, species diversity, plant cover, and vegetation structure (the size and shape of plants) developed rapidly. Vegetation in 2005 ranged from herbs and scattered shrub cover in the severely disturbed pyroclastic-flow zone to the continuous canopy of young forest in tree plantations around the perimeter of the blast area. The story of this collective ecological response to the 1980 eruption of Mount St. Helens involves both successional change over time at individual sites and development of landscape patterns. The 1980 eruption provided a special opportunity for scientists from a variety of disciplines to study ecological survival and establishment after a large disturbance, but several caveats challenge efforts to integrate this information. Developing a synthesis of ecological responses to the eruption is complicated by three factors:

Geological and Ecological Settings of Mount St. Helens Before May 18, 1980

Volcanoes and volcanic eruptions are dramatic players on the global stage. They are prominent landscape features and powerful forces of landform, ecological, and social change. Vesuvius, Krakatau, Pompeii, and, in recent decades, Mount St. Helens hold an important place in our perceptions of how the Earth works and the incredible, destructive effects of violent eruptions. Perhaps less appreciated is the great diversity of interactions between volcanoes and the ecological systems in their proximity. Volcanic activity and ecological change at Mount St. Helens have been particularly dynamic and instructive. Frequent eruptions of diverse types have interacted with terrestrial and aquatic ecological systems to display a broad range of responses (Franklin and Dyrness 1973; Mullineaux and Crandell 1981; Foxworthy and Hill 1982). Leading up to the 1980 eruption of Mount St. Helens, Cascade Range volcanoes of the Pacific Northwest of the United States were the subject of a good deal of study for objectives that were both academic and applied, such as assessing volcanic hazards and prospecting for geothermal resources. The fauna and flora of forests, meadows, lakes, and streams of the region were generally well known and described. The 1980 eruption put a spotlight on Mount St. Helens, as the world watched volcanic and ecological events unfold in real time. These events also stimulated an interest to better understand the volcanic and ecological conditions that existed before 1980. The geological, ecological, and historical settings provide context for interpreting the physical and ecological responses following the 1980 eruption. [Here we use the term history in the broad sense to include geological time as well as recorded human history.] Study of any ecological system should start with consideration of its context in space and time and in geographical, geological, and ecological dimensions. From a geographical perspective, the position of Mount St. Helens in a north–south chain of volcanoes along a continental margin sets up strong east–west geophysical and biotic gradients between the sea and mountain top and along a north–south climate gradient (Figure 2.1). Understanding of these broad gradients is useful in interpreting similarities and differences among different parts of a region. These gradients also organize fluxes of materials, organisms, and energy across broad areas. Marine air masses, for example, deliver water to the continental edge, and this abundant moisture flows back to the sea, forming a regional hydrologic cycling system. A well-connected marine– freshwater system fostered development of numerous stocks of anadromous fish. Similarly, the north–south climatic gradient and topographic features of mountain ranges and chains of coastal and inland wetlands form travel corridors for migratory birds. Movement of such wide-ranging terrestrial and aquatic species results in a flow of nutrients, propagules, genes, and organisms in and out of local landscapes within the region and even more widely. Past activity of a volcano influences its surroundings and affects biophysical responses to new disturbance events. Legacies of earlier eruptive activity may be expressed in landforms, soils, lakes, streams, animal communities, and vegetation patterns. This pattern is especially true at Mount St. Helens, which has erupted about 20 times in the past 4000 years (Table 2.1 on page 16). Vestiges of both the preeruption ecological systems and recent eruptive activity can strongly influence the posteruption landscape and patterns of change in ecological systems. Across the region and over evolutionary time scales, climate and biota interact with disturbance regimes of fire, wind, floods, volcanism, and other agents. Thus, the ecological history of the local area and its regional context determine the pool of species available to colonize a disturbed area, the capabilities of those species to respond to disturbance, and the array of types and configurations of habitats available for postdisturbance ecological development. Given the importance of spatial and temporal context, this chapter begins the analysis of ecological responses to the 1980 eruption of Mount St. Helens by describing the area before 1980. Our objective in this chapter is to set the stage for subsequent chapters, which detail the geological events and ecological responses unfolding on May 18, 1980, and during the subsequent quarter century. We characterize the Mount

Volcano Ecology: Disturbance Characteristics and Assembly of Biological Communities

Volcanic eruptions are major agents of change to earths ecological systems. Lava flows, tephra deposition, lahars, and other volcanic processes function as ecological disturbance agents that vary in their intensity, spatial extent, and impacts to ecosystems. Typically, in the aftermath of volcanic disturbance legacies of organisms and other organic matter survive from the pre-disturbance ecosystem and these can profoundly influence post-eruption ecosystem assembly. In cases such as volcanoes emerging from beneath the sea or where there are thick pumice deposits or lava flows, primary ecological succession occurs on entirely new substrates. The course of ecosystem response is regulated by nutrient limitations, available colonists, climate, biotic interactions, and other factors. Of the 404 volcanoes with reported eruptions since the famous 1883 eruption of Krakatau, only 11% have published ecological studies, and of those only three iconic volcanoes – Krakatau, Surtsey and Mount St. Helens – have been subjects of long-term, multi-taxa ecological studies.

Ecological Perspectives on Management of the Mount St. Helens Landscape

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 landand water-management issues. The sequence of management issues at Mount St. Helens forms a framework for considering the perspectives and roles of environmental scientists in management of the area. Before March 20, 1980, 123 years had elapsed since the previous eruption of Mount St. Helens, and management of the area focused on recreation and forestry for wood production. Between March 20 and May 18, 1980, the mountain underwent a period of mild volcanic activity, and concern focused on the hazards it posed to people and property. Immediately after the massive eruption, search and rescue efforts became all consuming. Thereafter, concerns gradually shifted to long-term management of the hazards and the commercial, educational, recreational, and research opportunities of the area. During this period, environmental scientists became strongly engaged. During the first few years after the initial eruption, their engagement was highly energetic. The pace of their engagement decreased to quite modest in the mid-1980s and to very little in the 1990s and 2000s. These shifting roles were influenced by changes in the eruptive behavior of the volcano; the progress of construction projects to minimize hazards; and the rate of geomorphic and ecological change in uplands, rivers, and lakes. In this chapter, we present a brief synopsis of the roles of environmental scientists in management issues related to the 1980 eruption of Mount St. Helens. First, the chapter describes the geographic and temporal contexts of the eruption and surrounding landscape. Then, it reviews selected examples of hazardand land-management issues involving environmental sciences and scientists. Finally, it summarizes the advisory role of environmental scientists in protecting natural processes and features, human life, property, and commercial development. The discussion focuses on the posteruption period when environmental scientists were most active and when the ecological changes considered in this book were taking place.

Posteruption Arthropod Succession on the Mount St. Helens Volcano: The Ground-Dwelling Beetle Fauna (Coleoptera)

Arthropods are important components of ecosystems because of the roles they play in pollination, herbivory, granivory, predator–prey interactions, decomposition and nutrient cycling, and soil disturbances. Many species are critical to the structure and functioning of their ecosystem, although some (particularly insects) are considered pests in farmlands and forests because of their detrimental effects from feeding on foliage and transferring pathogens to trees and crops. Arthropods also constitute a high-protein prey resource for vertebrate wildlife (especially small mammals, birds, reptiles, and amphibians), thus contributing to the existence and stability of thesewildlife species. As such, studies of arthropod population dynamics and changes in species assemblages following natural disturbances are important for understanding ecosystem responses. In the case of the Mount St. Helens volcanic eruption, studies of arthropods not only can provide information on natural history and ecology of many different species but also are relevant for evaluating theories of disturbance ecology and postdisturbance successional processes. The 1980 eruption ofMount St. Helens provided researchers with an opportunity to test a wide range of theories concerning the structure and functioning of ecosystems. In particular, the existence of a continuum of disturbance intensity across a large landscape made possible a suite of comparative studies that evaluated the influence of different levels of volcanic disturbance on the survival and initial recolonization patterns of plants and animals. For example, researchers to date have documented the survival and reestablishment of a number of plant species and described the patterns and rates of vegetation successional processes of the disturbed ecosystems (see Lawrence, Chapter 8, this volume;Antos andZobel, Chapter 4, this volume; Dale et al., Chapter 5, this volume; del Moral et al., Chapter 7, this volume; and references therein). In addition, numerous faunal studies havequantified the eruption’s impacts on survival and subsequent short-term responses of small mammals (Andersen 1982;Andersen andMacMahon 1985a,b; Adams et al. 1986a; Johnson 1986; MacMahon et al. 1989; Crisafulli et al., Chapter 14, this volume), birds (Andersen andMacMahon 1986), amphibians (Karlstrom 1986; Hawkins et al. 1988; Crisafulli and Hawkins 1998; Crisafulli et al., Chapter 13, this volume), and arthropods (Edwards et al. 1986; Sugg 1989; Edwards and Sugg 1993; Crawford et al. 1995; Sugg and Edwards 1998; Edwards and Sugg, Chapter 9, this volume). Information collected on the fauna and flora of Mount St. Helens during the past 20 years facilitates the analysis of recolonization patterns in the context of two ecological theories: relay successional processes (MacMahon 1981) and the intermediate-disturbance hypothesis (Connell 1978). The term relay succession refers to the sequential replacement of species (plant and animal) in an ecosystem recovering from some form of disturbance. This process typically begins with species that either survived the disturbance or immigrated to the site shortly thereafter. Some of these species are well adapted to the disturbed conditions of the site and can greatly increase in abundance, whereas others are poorly adapted and become locally extinct. Biotic interactions (competition, predation, herbivory, and parasitic and disease infections), coupled with abiotic factors (extremes of temperature or moisture), often determine the success or failure of each species survival. Through time, as different species colonize the site, they alter the environment’s characteristics (e.g., plant regrowth provides shade, cools soil surface temperatures, increases soil moisture and organic matter, and provides substrate for fungi and vegetation for herbivores). As the environmental conditions change, new opportunities are created for additional species to colonize and dominate, eventually replacing established species that have become competitively inferior in the altered environment; hence, the “relay” of species during postdisturbance succession. This process applies to both plant and animal species assemblages and inherently involves complex interactions among plants and animals (MacMahon 1981). The second theory, the intermediate-disturbance hypothesis (Connell 1978), addresses the patterns of species richness

Posteruption Response of Phytoplankton and Zooplankton Communities in Spirit Lake, Mount St. Helens, Washington

Abstract Spirit Lake, Washington was radically altered limnologically by the May 1980 eruption of Mount St. Helens. The eruption provided a rare opportunity to study lake response and recovery in the wake of volcanic disturbance. During the eruption, and for several months thereafter, phytoplankton and zooplankton populations were subjected to extremely deleterious conditions. Consequently, these populations were virtually eliminated except for remnant organisms that somehow survived. During the next two years, the phytoplankton community and presumably the zooplankton community were comprised of only a few opportunistic species whose combined abundance was low. By 1983, however, phytoplankton abundance and species diversity had greatly increased due to increased lake-water transparency and increased availability of inorganic nitrogen. The reestablishment of the zooplankton community was also well underway by 1983, as indicated by the abundance of some species and the presence of most taxa that existed prior to the May 1980 eruption. By 1986, the phytoplankton and zooplankton communities were beginning to resemble those found in subalpine, oligotrophic/mesotrophic lakes in the Washington-Oregon Cascades. The rapid recovery of Spirit Lake demonstrated the vigor and resiliency of lake ecosystems and particularly plankton communities.

Soil Carbon and Nitrogen and Evidence for Formation of Glomalin, a Recalcitrant Pool of Soil Organic Matter, in Developing Mount St. Helens Pyroclastic Substrates

Formation of stable soil organic matter is typically the result of a relatively slow series of decomposition processes that can be constrained in early successional sites. Alternatively, compounds such as glomalin, a glycoprotein produced by arbuscular mycorrhizal fungi, may form relatively early during soil development and improve aggregate stabilization, water infiltration, and carbon and nitrogen storage. After 31 years of development, significant amounts of soil C, N, and BRSP, an indicator of glomalin, had accrued in pyroclastic deposits, in patterns affected by both plant community type and soil depth. Mycorrhizal fungi are important, but incompletely understood, drivers of pedogenic processes during primary succession and may exert disproportionate effects on soil processes and plant development prior to the accumulation of humified soil organic matter.