Ecology of Mount St. Helen's National Monument
On May 18,1980, Mount St. Helens went from a dormant volcano with a vibrant surrounding ecosystem, to a site of destruction. The volcanic eruption decimated the landscape surrounding Mount St. Helens, mowing down entire forests and their habitats. The eruption was the deadliest and most economically destructive volcanic event in U.S. history.[1] First, heat and poisonous gas from the volcano sterilized the land surface and then the land was buried under many meters of ash, mud, and rock. Within a few miles of the collapsed Mount St. Helens, nearly every living creature perished.[2]
Though the eruption brought great destruction to the natural ecosystem surrounding Mount St. Helens, the aftermath shows the resilience of species and their ability to adapt to new environments. Traces of life including seeds, spores, gophers and fungi were able to survive beneath the debris of the volcano. Flora and fauna located at the edge of the destruction zone were also able to survive. And so, following the eruption and its resulting destruction, life has returned and flourished at Mount St. Helens.
Mount St. Helens Volcanic Monument was established in 1982 within the Gifford Pinchot National Forest, designating the 110,000 acres (445 km2) around Mount St Helens for research, recreation, and education.[3] The area inside the Monument has been left to naturally respond to the environmental factors resulting from the eruption of 1980 providing a scientifically significant demonstration of natural ecological recovery.
The 1980 volcanic eruption
The eruption of Mount St. Helens began with a series of small earthquakes in mid-March of 1980 followed by the peak eruption on May 18th which resulted in a flank collapse, avalanche, and explosion.[4] The eruption blasted away over a thousand feet of the mountain’s summit, destroyed forests, and claimed the lives of 57 people. Hot volcanic debris (comprised of gases and rocks) was blasted over 230 square miles (600 square kilometers) with hurricane-force winds that blew down the forests in its path.[5] The avalanche buried 14 miles (23 kilometers) of the North Fork Toutle River with rocks, dirt, and trees. Throughout the southern half of the mountain, volcanic mudflows (lahars) poured down the rivers and gullies.[6] The eruption and its aftermath impacted land as far as 17 miles (27 kilometers) from the summit. From the blown and burnt trees, about 4.7 billion board-feet of timber were lost with millions of board-feet still floating across Spirit Lake today.[7] Around the blow down, the ground was covered with tephra and ash. Further away, the trees that had not blown over were killed by the heat of the blast forming a “ghost forest”: a fringe of standing, dead, ash-covered trees.[8] The destruction resulting from the eruption gained worldwide attention, but it is the results of the eruption that keep Mount St. Helens such a relevant and exciting ecological topic today.
Post eruption
New appearance
While the mountain was once known for its conical symmetry, after the collapse of its northern slope, Mount St. Helens now has a gaping crater. Beyond changes in physical appearance, the ecology of the mountain was forever altered. What immediately was left from the volcanic event was a collage of disturbance zones ranging from areas with high survival rates to zones now devoid of all life. It is important to recognize that the ecology was not erased, with flora and fauna eventually able to achieve ecological recovery.
Story of survival
Beginning as a story of significant destruction, the aftermath of the immense disturbance demonstrates the resilience of life. Not all species survived, with organism survival depending on local site conditions, characteristics of disturbance processes and biological factors.[9] Despite larger species suffering greater mortality rates, species from all primary trophic levels survived (including herbivores, predators, scavengers, and decomposers). This allowed complex food webs to develop in the post-eruption emerging ecosystems.[10] Water, sunlight and time became the basic ingredients for vegetation to return to Mount St. Helens. Beginning with the surviving seeds, spores, gophers and fungi that were able to survive the volcanic eruption, mosses, grasses, shrubs, and trees were next to follow. The elk, fish and tourists have since returned to the region as well.
Patterns
Several patterns have emerged in the ecological response of the untouched Monument since the eruption. In general, aquatic systems rebounded much faster than terrestrial ones, with lakes responding quicker than streams and rivers. The volcanic and forest debris caused reduced productivity for lakes located in the blast zone. As the debris settled, organisms responded to the influx of nutrients and within a few years, water quality had returned to levels similar to those found in undisturbed lakes in the area[11]. Since the 1980 eruption, most lakes and streams have largely returned to the typical ecological conditions of the northwest region. While the eruption vastly changed the ecological response, secondary disturbances including small landslides and river channels shifting have created a complex landscape college in the years after the initial disturbance.[12]
Zones of environmental recovery
NASA’s Landsat satellite series captured imagery of the eruption blast zone between 1979 to 2016. These satellite images helped in identifying noticeable vegetation recovery sites. The first noticeable recovery occurred in the late 1980s in the northwestern quadrant of the blast zone. This is the land area furthest away from the volcano, so it is unsurprising that it was the first recovery location. During the late 1990s, the terrain east of Spirit Lake was considerably greener. By the end of NASA’s series in 2016, the only area beyond the slopes of the mountain itself that remained bare at the scale of the satellite videos was Pumice Plain. From ground surveys, it was discovered that even this area – that appeared barren –[ also had life returning to it. In the years following the explosion, the river has re-carved a shallow, braided path through the once buried valley[13] and several forests have come back so well that some sections are now being commercially thinned.
Species
The species that were able to survive the eruption and subsequent disturbances had similarities including size, biological factors and migration patterns. In the blast area, survivors were mostly plants with underground buds, animals who were small below-ground dwellers, and organisms protected by snow. Smaller organisms were favored, even smaller individuals within a species as large overstory trees perished while smaller saplings of the same species were able to survive in numerous locations.[14] A large number of below-ground dwellers (including pocket gophers and deer mice) as well as ground dwelling insects and spiders were able to survive the explosion. These organisms played a vital role in ecological recovery, with species such as prairie lupines (on the Pumice Plain) and pocket gophers (in the blown-down forests) facilitating colonization of other species and slowly repopulating Mount St. Helens National Volcanic Monument[15].
Pumice Plain, one of the slowest zones to recover, has gradually had vegetation reintroduced, beginning with the prairie lupine. Prairie lupines are small wildflowers that have a special adaption which allows the plant to take nitrogen (a critical nutrient for plants) straight from the air (while most plants get nitrogen from soil). Prairie lupines were able to catch blowing leaves and other organic matter from the air (including dead plants and insects). Through this process, Prairie lupines created small pockets of soil on the old volcanic deposits. Slowly, the process of ecological recovery is underway in Pumice Plain.[16]
Lessons learned from Mount St. Helens 1980 eruption
While aspects of the Mount St. Helens eruption were tragic, scientists view this natural disturbance as crucial to ecological processes. This was the first eruption in the continental US during modern scientific observation to create a unique and significant opportunity for study[17]. The eruption (as a natural disturbance) plays an important role in maintaining biological diversity and as one ecologist put it, “disturbance drives forest ecosystems”.[18]
Factors determining survival and recovery
The 1980 Mount St. Helens eruption was a significant educational moment for scientists regarding species’ survival. The eruption occurring in the early morning protected nocturnal animals in their subterranean retreats. The spring timing meant there was snow and ice to protect species.[19] Additionally, certain life history attributes favored survival such as some anadromous fish and migratory bird populations not being present for the eruption.
The area has since become a natural observatory as scientists study how plants and animals are able to rise from the ashes, re-colonize and flourish again. The diversity and techniques for survival by the organisms was remarkable. For example, a mudflow carrying a log provided opportunity for the rapid transportation of nutrients, fungi, microbes and even small animals to new zones of Mount St. Helens devoid of life. Whole plants were able to regenerate from root fragments carried downstream and these small groups of surviving species began to create islands of life.[20] While scientists at the time of the eruption believed plants and animals from the edges of the less disturbed areas would eventually repopulate the landscape, what actually occurred was recolonization by species who survived the blast and formed the new pockets of life. Over time, the protected oases they created formed into larger patches and created a complex pattern of plant and animal communities.[21]
The eruption demonstrated the importance of “biological legacies” or the remnants of the old landscape that were able to survive and play a significant role in creating new islands of life. These biological legacies are being incorporated into forest management. Ecological succession is very complex; it occurs on many different time scales and along diverse paths, and is dependent on many chance factors.[22]
Unique example of natural recovery
While Mount St. Helens Volcanic Monument was protected from human influence, areas immediately outside this protected area were still impacted by the eruption but open to human involvement. Scientists were able to study and learn from the differences between natural and human involved ecological recovery.[23] Many scientific assumptions following the eruption regarding the ecological restoration without human interaction have proven to be incorrect.[24] Some people wanted rapid salvage logging due to fears about fire and insect outbreaks in the thousands of acres of dead trees in the Monument; however, scientists have learned the volcanic ash that coated the dead trees reduced flammability and acted as an insecticide.[25] Scientists could never create this type of ecological restoration, and rely on natural examples to teach them.
Mount St. Helens remains an active volcano today.[26] Ecologists continue to use the site to learn about recovery patterns for trees that can be used for future ecological restoration of logged-over forests throughout the Pacific Northwest.[27] Living and dead biological legacies (such as dead trees and rotten logs) are significant for the ecological response after major disturbances like the 1980 eruption.[28] Natural disasters create new habitats and initiate forest succession therefore controlling and driving forest ecosystems. This shows the vital role events such as the volcanic eruption of Mount St. Helens play in maintain forest biological diversity.
