Research About blowdown zone

Posted On: Filed Under: Biological Research

Ecology of the tadpoles of the tailed frog (Ascaphus truei)

Data on the microhabitat parameters, especially pertaining to flow rate and substrate characteristics, of the stream-inhabiting tadpoles of the tailed frog (Ascaphus truei) were collected at two tributaries of Clearwater Creek at Mount St. Helens, Washington and at Parker Creek on Mary’s Peak, Benton County, Oregon. This is the only tadpole in North America that is highly specialized for maintaining position and feeding from algae while attached to rocks via an enlarged oral disc with many rows of labial teeth. Positions of tadpoles in the streams were correlated with oral morphology and associated anatomy. Because of the length of the larval period of Ascaphus, there are usually 2 to 3 yearly cohorts in the streams at one time. We hypothesized that the interaction of the abilities of the tadpoles to adhere to rocky substrates and the size of the tadpole would result in microhabitat segregation. Whether small or large tadpoles occupied fast versus slow water would depend on the growth pattern of the tadpole (drag) versus the changes of the adhesive abilities with size.

 

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Recovery of mycorrhizal associations on Mount St. Helens.

This work has studied the recovery of mycorrhizal associations on Mount St. Helens since the eruption in 1980. Mycorrhizal associations are symbioses between plants and fungi localized on the roots of plants. The fungi provide much of the nutrients utilized by the plants and the plants provide carbohydrates to the fungi. The associations on Mount St. Helens range from those plants that form facultative mycorrhizal associations, many herbaceous species including Lupinus lepidus, L., latifolius, and Epilobium angustifolium, to the coniferous trees that are obligately dependent on mycorrhizae.

 

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Disturbance and recovery of soil, microbial, and plant processes.

Our work has focused on disturbance and recovery of soil, microbial, and plant processes following volcanic disturbance. Particular emphasis was placed on spatial relationships involving the carbon and nitrogen cycles. Comparative studies have been conducted at six sites that were disturbed to varying degrees by the May 1980 eruption of Mount St. Helens. These sites include Butte Camp, Upper Pine Creek, the Lahar on the Muddy River, the former Timberline parking Area, and Meta Lake.

 

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Natural revegetation of debris avalanche and lahar (mudflow) deposits

Natural revegetation was studied on debris avalanche and mudflow deposits primarily northwest and southeast of Mount St. Helens on Forest Service land. Objectives were: 1) examine patterns of revegetation in response to large and small scale surface changes as deposits are modified by geomorphic processes; 2) characterize revegetation on different types of sites in the devastated area (North Fork Toutle River debris avalanche and Muddy River mudflow) and 3) establish a system of documented permanent plots to track ecosystem recovery and describe important processes through time.

 

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Natural revegetation of upland portions of the blast zone

Natural revegetation was studied within the northeast sector of the blast zone on Forest Service land. Objectives were: 1) compare revegetation on major disturbance types (pyroclastic flow, debris avalanche, blown down and standing dead forest); 2) examine the effects of pre-eruption plant communities and the presence/absence of snowpack on current vegetation; 3) establish a system of permanent plots to track ecosystem recovery and describe important processes through time.

 

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Arthropod recolonization of Mount St. Helens.

Ashfall and blast zone sites have been sampled in order to monitor the recovery of insect and spider populations reduced by the May 1980 eruption. There were many survivors of the eruption in ashfall sites, especially of sedentary species and others that were protected in micro-refugia. Mortality in arthropod populations was correlated with the depth of the ashfall. Using ant colonies as an index, areas with 15 cm or less of ash deposited had species numbers similar to sites outside the devastated area. However in all areas arthropod populations have remained low compared to arthropod population recovery following clearcutting.

 

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Effects of hillslope erosion on revegetation and sediment influx to the Toutle River

The 1980 eruption of Mount St. Helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km2 area. After the eruption, rates of erosion and plant cover were measured on tephra-covered hill slopes north of the volcano, some of which had been subject to one of three land-management practices. Rill erosion was initially greater than sheetwash, but its importance decreased comparatively quickly. On hill slopes left undisturbed since the eruption, rill erosion and sheetwash underwent a rapid and early decline due to the development of a stable rill network and the exposure and creation of more permeable and less erodible substrates. This decline was independent of plant recovery. Logging of trees downed by the eruption and scarification of the surface in preparation for reforestation slowed erosion, although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented. An experimental grass seeding program gave rise to a plant cover only after erosion had slowed, and then only in a limited range of environments.

 

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