Research About pyroclastic flows

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Effect of herbivores on Sitka willow and associated plant and animal communities and soils.

The invasion of trees and shrubs in early succession is often transformative because of their potential to outcompete early pioneers, provide animal habitat, influence nutrient cycling, and occupy sites over long time spans. The extent to which insect herbivores influence such successional transitions is unknown. We are investigating whether herbivory by a pair of stem-boring insects may substantially impede the structural dominance of Salix sitchensis, the first abundant woody colonist on a large primary successional site at Mount St. Helens volcano, Washington, USA. We also quantify vegetation and soil development at these same sites. Our collaborator Charlie Crisafulli (USFS) quantifies bird use of these sites, eventually allowing us to link herbivore effects on vegetation to bird habitat.

 

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Dynamic Spatial Patterns During Succession: Resolving Patterns and Mechanisms using Grid-Based Spatial Automata Models

(Project Summary from NSF Research Grant). Our major objective is to investigate how the spatial relationships among individual plants contribute to successional dynamics and influences the spatial patterns that result. We propose to investigate the effects of spatial interactions at the individual level on population dynamics and ecosystem succession on the Pumice Plain near Mount St. Helens, Washington. Spatial analyses of annual field survey data will test the significance of number, size, and species of neighboring plants on growth, survival, and recruitment. Computer models using grid-based spatial automata will implement alternative life histories and individual-level interactions to simulate spatial dynamics during primary succession. The results of this study will provide insights into integration of spatial dynamics across three levels of ecological organization: at the individual level, spatially modified growth rates; at the population level, spatially modified recruitment and mortality; at the ecosystem level, dynamic spatial patterns during succession.

 

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Insect colonization and invasion in the recovering devastation zone of Mount St. Helens.

Vegetation patches at Mount St. Helens represent discrete islands that are a focus for interactions among plants and insects. Our continuing studies focus on the role of biotic interactions (plant-herbivore and predator-prey), dispersal, and disturbance in this highly fragmented landscape. In the 1997 field season, we aim to address two primary questions: 1) What factors have allowed exotic ladybird beetles to displace native ladybird species within the monument? and 2) How does the size of vegetation patches influence colonization by insect species?

 

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Development of vegetation on barren and high elevation sites.

This study is a continuation of work begun in 1980. Current studies include monitoring permanent plots, monitoring grids, studying relict plots, assessing vegetation in potholes, and describing vegetation along transects. The plots studied to date can be divided into those that are fully recovered, those undergoing secondary succession and those undergoing primary succession. The rate of recovery, measured by the number of species and their cover, is related to proximity to sources of colonists and to habitat stress. The species composition of sites undergoing primary succession is related to proximity to intact vegetation and is strongly affected by distance and by chance effects. Previous studies have demonstrated that environmental factors only weakly predict species composition.

 

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Patterns and mechanisms of early plant primary succession on the pumice plain.

Primary colonists and mechanisms of their arrival to the pumice plain have been monitored since 1986. Measurements of seed rain have shown that the most common wind dispersed species arriving on the pumice plain are Anaphalis margaritacea, Epilobium angustifolium, and E. watsonii. Of the early colonists A. margaritacea is the most wide spread species, but Lupinus lepidus is the most abundant species. In addition the L. lepidus population is increasing dramatically.

 

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Natural establishment of conifers at Mount St. Helens

This study tracks the establishment, survivorship, and growth rate of colonizing conifers on substrates deposited during the 1980 eruption of Mount St. Helens. Two 50 x 50 meter plots were installed at sites on the pyroclastic flow north of the crater and the upper portion of the Muddy River mudflow during 1989 and 1990. Two 50 x 50 meter plots were installed on the debris avalanche in 1993 and 1994. In each plot all individual trees are identified to species, measured (total height and stem diameter at ground level), and tagged.

 

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Demography of Lupinus lepidus on the pumice plain and its role in primary and secondary succession.

This study details the demography of two populations of Lupinus lepidus, a primary successional plant species growing on the Pumice Plain, and also investigates the role lupine plays in the recruitment of additional species through facilitation. Lupine and other plant species’ populations have been censused once or twice each growing season from 1982-1991. Prairie lupine was the first species to colonize the barren deposits of the Pumice Plain and attained extremely high densities in certain portions of our plots during the census years.

 

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Community reassembly following volcanic disturbance: the ground dwelling beetles (Coleoptera)

This study documents the recovery of beetles within the volcanically disturbed areas of Mount St. Helens and should provide an index to the rate and stage of ecosystem recovery at various points in time since the eruption. Beetles are ideal for monitoring ecological recovery following disturbance as they represent a broad trophic array. The ground dwelling beetle fauna of forests and clearcut habitats were sampled using pitfall traps (10 traps/site) that were open from the time of spring snow melt to early autumn from 1982-1984 and again in 1987 and 1990. Sites sampled include undisturbed “reference” areas and three post-eruption habitats (ashfall, blowdown, and pyroclastic/debris flow).

 

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Small mammal recolonization on the Mount St. Helens volcano

The purpose of this study was to systematically document the initial survival and the subsequent recolonization of small mammal species into disturbed regions of Mount St. Helens, and to ascertain differences in early successional patterns among various habitat types and levels of disturbance. Trapping efforts have documented the recolonization of small mammals {Rodentia, Insectivora, Lagomorpha and Carnivora (Mustelidae)} into representative sites of four broadly defined montane habitats (forests, clearcuts, subalpine meadows and riparian ravines) that were subjected to increasing degrees of volcanic disturbance (undisturbed, ashfall, mud flow, tree blowdown, and pyroclastic/debris flow).

 

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Contributions by lupines to volcanic soils.

The effects of colonization of Lupinus lepidus and L. latifolius on carbon, nitrogen, and microbial activity in volcanically disturbed soils was investigated in several studies. Examination of nitrogen fixation rates showed that both species have diurnal and seasonal fluctuations that appear to be associated with environmental factors. Nitrogen fixation rates are highest during daylight and early in the growing season, and the seasonal pattern is reflected in carbon and nitrogen levels; that is, as nitrogen fixation increases, carbon and nitrogen production increases. First year plants of both species fix similar amounts of nitrogen.

 

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