Research About blowdown zone

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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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The herpetofauna of Mount St. Helens: survival and colonization following the 1980 eruption.

This study documents the survival and colonization of reptiles and amphibians in areas impacted by the 1980 eruption of Mount St. Helens. Surveys were conducted at 15 locations, with representative sites in three distinct volcanic impact zones, 1) ashfall, 2) blowdown, and 3) blast, during spring and summer from 1980 through 1991. Twelve species of herptiles (9 amphibians, 3 reptiles) are considered to have survived volcanic influences ranging from the directed blast to the accumulation of ash in otherwise unaltered habitats. These survivors represent most of a hypothetical list of 16 species considered to have occurred in the area before the eruption. Generally, surviving species were characterized by being more aquatic than those not found and this was attributed to the thermal buffering capacity of cool ice and snow covered aquatic systems where individuals were protected from the hot volcanic gases.

 

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Recovery of riparian vegetation at Mount St. Helens

This study documents rates and patterns of vegetation recovery at lakes and streams in the blast zone of the May 1980 eruption. Recovery of streamside vegetation was dominated by plants that resprouted from below ground parts that survived the blast. Depending upon frequencies and intensity of secondary disturbances, revegetation from seeds has become increasingly important. Flooding, battering, and deposition of reworked tephra have extremely important effects on streamside revegetation. Recovery rates are more rapid at greater distances from the volcano where blast effects were less devastating.

 

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Stream channel adjustments in the Smith – Muddy River drainage after the 1980 Mount St. Helens eruptions

Stream channel response to the 1980 eruption of Mount St. Helens has varied widely. Stream channels that received only airfall deposits have shown no significant sedimentation following the eruption. In drainage basins that received both blast and airfall deposits, localized channel modification has been observed. However, as the blast/airfall deposits are predominately sand-sized, they have been quickly removed from the steep low-order channels surrounding the mountain with little net effect on pre-eruption channel morphology. Some subsequent channel modification has resulted in lowered gradient reaches downstream as sediment eroded from upstream hill slopes and stream channels has been redeposited in these reaches. Long-term effects in blast/airfall affected streams appear limited to channels subjected to debris torrents resulting from shallow-seated landsliding and breakup of in-channel debris jams.

 

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Recovery of stream ecosystems following catastrophic disturbances

This study was conducted in the Clearwater basin of Mount St. Helens. Three projects within the study investigate recovery of trout and sculpin populations, tailed frog populations, and invertebrate populations. Trout were studied in the main channel of Clearwater Creek, and the effects of large woody debris in the stream on fish populations were examined. Trout populations were still low as of 1990, being one-tenth to 20% of that in undisturbed stream systems; this appears largely due to interruption of spawning in years following the blast and to continuing lack of spawning habitat. Trout densities were found to be higher in areas with lots of woody debris. The condition of trout was high throughout the stream in years since 1984 presumably due to rapid recovery of high abundance of invertebrate prey. By 1985 sculpin densities were as high as or higher than in undisturbed streams.

 

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Distribution of plant detritus and recovery of plants in deposits of May, 1980 eruption of Mount St. Helens

This study seeks to identify types and sizes of plant material and distance and means of deposition in the May 1980 blast of Mount St. Helens. Types of plant material included pieces of moss, leaves, stems, roots, tree branches and trunks. Four types of transport were identified. The debris avalanche deposited plant material 23 km away. Mudflows (lahars) carried material 75 km to the Columbia River. The pressure blast removed vegetation in a 500 km2 area. Pyroclastic flows in conjunction with the plinian column spread plant debris for at least 75 km in a 110o arc to the north and east. These results are being compared with fossilized records of volcanic eruptions worldwide but especially those from Tertiary western United States.

 

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Animal use of dead and down timber

Snags and blowdown trees that were killed by the May 1980 eruption were marked for future study. Objectives were to document animal use of snags and down timber and to observe changes in decay stage and wood nutrient status. Sound trees with bark and branches intact were originally marked in several areas of blowdown and standing dead zones.

 

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Recovery of aquatic insect communities in streams near Mount St. Helens

We have monitored stream insect communities from 1980 to 1988 in Clearwater Creek, Elk Creek, and Ape Canyon. Quantitative and qualitative samples indicate rapid colonization in 1981-82, and then a gradual increase in richness and diversity. Over 200 taxa have now been collected from Ape or Clearwater Creeks.

 

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Effects of pocket gopher (Thomomys talpoides) mounds on plant reestablishment processes.

This studydocuments that pocket gophers in the blast zone did survive the May 1980 eruption of Mount St. Helens, and they did have an effect on early plant re-establishment within the blast zone. One study site is approximately 20 km northeast of the volcano. This site received a layer of pumice and ash to an average depth of 12 cm in 1980. Vegetation on gopher mounds was compared to that on surrounding un-mounded soil surface. Findings show that species composition is different; there are more residual species on mounds, and seedlings on mounds are more likely to survive and contribute to future local population growth.

 

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