Ecological Succession in Mount St Helens

by Jessica Liang

The word eruption cultivates mental images of catastrophic events, and perhaps more close to heart, and eruption of Mount St. Helens. But despite the enormous destruction and loss wreaked by this eruption, it also set forth an equal potential for creation. The eruption created a unique opportunity for scientists and researchers to study the changes the natural destruction wrought on the landscape. Most notably, scientists now had a unique opportunity to observe the process of succession first hand and reevaluate their theories based on their findings. By examining surviving population such as zooplankton, elk, and newly developing plant colonies such as Lepidus, researchers could gain great insight on biological change that can be used to ”make sensible suggestions for management” of natural disaster legacies (Nash 2010).  The eruption of Mount St. Helens is infamous for the destruction wrought on the surrounding areas; however it has also given rise to the development of a host of possible new ecological systems, reset the evolutionary clock, and allowed scientists to witness the actual process of ecological succession.

Sapling breaking through ash layer after the eruption of Mout St. Helen. Taken by Jerry Franklin, United States Forest Service 1980s.

The 1980 eruption transformed the once lush environment surrounding the mountain into a steaming refuse covered landscape, and yet organisms quickly sprung forth from this treacherous territory. Succession is the predictable and orderly change in composition and structure of an ecological community, and the eruption of Mount St. Helens allowed scientists to conveniently study succession and create new biological theories of this process. These theories could then become invaluable in the study and reconstruction of other disaster ridden ecosystems. One reporter, Rowe Findley writes in his article “Mount St. Helens,” “I still see the bleaching trunks of giant conifers laid down in a radial pattern by the expanding wave of the blast. But I also see many signs of resurgent life-extensive greening slopes in the far distance and major plant colonies closer at hand” (Findley 2000). This regeneration of species in an area so barren after the eruption is as the essence of succession. As a result scientists were able to witness events that often take place over thousands of years ago. Previously, the theory of succession was a fairly simple and predictable process. As Steve Nash writes in “Making Sense of Mount St. Helens”, “Logical rules had been laid out from these studies: Simple organisms arrive first, giving way to more complex ones”. Simple opportunistic species will first populate an area and changing the landscape so that it is more inhabitable by other species that compete to become the dominant stable species in a particular area (Nash 2010). However in reality this was not necessarily the case- often, Species arrived earlier or later than expected, and some appeared that had not been predicted at all. Scientists and ecologists at the sites had to learn and take into account complexity to more fully understand the situation, and accept that a set series of events does not have to take place for the same result to occur. While the research challenged many biological theories, it helped aid in understanding and dealing with disturbances such as mudslides and forest fires by showing what conditions encouraged growth and recovery and where money should be spent to aid the process.

Ash particle from Mount St. Helens. Taken by United States Geological Survey 23 Jan. 2008.

The eruption led to a wide variety of research studies investigating the area’s organisms, and had interesting effects on the post eruption conditions affecting these populations. In this first experiment Gaddy describes the effect of ash on zooplankton, small microorganisms that inhabit nearby lakes surrounding Mount St. Helens (Gaddy 1986). He does this by

recreating similar conditions of ash deposits on lakes to lab populations of a variety of zooplankton species and monitored their resulting filtration rates, ingestion rates, and assimilation efficiencies (Gaddy 1986). Although he did not find significant evidence that the ash radically changed any of these rates over time, he hypothesizes that perhaps the assimilation efficiencies would decrease due the higher percentage of ash resulting in a lower concentration of nutrients. In turn this may cause filtration rates to increase to compensate for the loss, immediately after ash was introduced to the system (Gaddy 1986).  Studies such as Gaddy’s help determine if the introduction of particle fraction to lake environments would negatively affect the inhabiting organisms and whether clean up of these areas is necessary to promote recovery.

Various species of Lupines. Taken by Olavfin.

Studies also show evidence the complexity and multiplicity inherent in paths of succession. In del Moral’s study on “Long-Term Effects of Lupinus lepidus on Vegetation Dynamics at Mount St. Helens” studies the how

the Pacific Lupine, a plant whose roots help fix nitrogen and improve the fertility of the soil, influences the growth of new species (del Moral 2005). This was done by sampling different colonies of Lupinus lepidus near the blast site of the eruption (del Moral 2005).  Del Moral found that Lepidus caused either a potential increase or decrease in the rate of succession, and further goes on to say that while Lepidus improved fertility of the area; it also had varying affects of other plant species due to the interactions between other plants and animals in the surrounding area (del Moral 2005).  His results also can be explained through complexity that had before this had not been attributed to ecological succession. Even more notably, it created the idea that succession does not just occur in one way, but many depending on the conditions, suggesting that attempts to influence succession may or may not create positive results.

Elk grazing. Taken by Jonathunder 22 May 2010.

The indications of the two previous cases do not simply apply small or simple organisms but other more complex specie populations. Merill’s study on “Elk Dietary Composition and Quality in the Mount St. Helens Blast Zone” further explores the effects of the eruption by discussing the repercussions of a changed plant population on the diets of Elk by comparing the nutrient consumption of Elk in the blast zone with other Elk populations in the west coast (Merrill 1995). She concluded that landscapes of primarily early succession stages provide high energy intake while old–growth landscapes provide low energy food sources that have adequate protein (Merrill 1995). These results, like the previous studies show the complexity of the situation- that one event does not have an overall good or bad effect on the surrounding areas. Through these studies ecologists have been able to gather data on succession and posit that stresses, such as removal of debris or sowing of seed, have a variety of consequences, ranging from a decrease in the rate of succession or an explosion of the rat population, on a given area, and many different factors must be taken into account before and effect can make sense (Nash 2010).

While the eruption of Mount St. Helens may have seemed wholly a destructive event for most, it created a unique glimpse into the complex process of succession. Scientists have learned much about the many factors and unexpected cases that commonly crop up and not have gained valuable insight in how to deal with future natural disturbances. The insight will further help them intelligently deal with many different situations that nature creates and allow them to help speed the recovery of an area after such disturbance. Even if many feel that the eruption of Mount St. Helens created and end of an ecological system, it is in fact a fresh start and a resetting a of a biological clock that allowed for great changes to occur in the area.

Wildflowers recover Pumice Plain, an area covered by volcanic ash. Taken from P. Frenzen, US Forest Service 2004.

Work Cited

Findley R. 2000. Mount St. Helens. National Geographic [Internet]. [cited 2010 Nov 2] 197(5): 106. Available from: http://ehis.ebscohost.com/ehost/detail?vid=1&hid=23&sid=3ed6fe16-213f-4fbd-9f49 045701f08f89%40sessionmgr11&bdata= JnNpdGU9ZWhvc3QtbGl2ZSZzY29wZT1zaXRl#db=sch&AN=3139682

Gaddy AJ. Parker RA. 1986. Zooplankton grazing activity and assimilation in the presence of Mount St. Helen’s ash. Northwest Sci [Internet]. [cited 2010 Nov 3]; 60(1): 47-51. Available from: Freely Accessible Science Journals: http://www.vetmed.wsu.edu/org_NWS/NWSci%20journal%20articles/1986%20 files/Issue%201/v60%20p47%20Gaddy%20and%20Parker.PDF

Merrill EH. Callahan-Olson A. Raedeke KJ. Taber RD. Anderson RJ. 1995. Elk (Cervus elaphus roosevelti) dietary composition and quality in the Mount St. Helens blast zone. Northwest Sci [Internet]. [cited 2010 Nov 2]; 69(1): 9-18. Available from: CSA Illumina: http://www.vetmed.wsu.edu/org_NWS/NWSci%20journal%20articles/ 1995%20files/Issue%201/v69%20p9%20Merrill%20et%20al.PDF

del Moral R. Rozzell LR. 2005. Long-Term Effects of Lupinus lepidus on Vegetation Dynamics at Mount St. Helens. Plant Ecology [Internt]. [cited 2010 Nov 2];181(2): 203-215 Available from: JSTOR: http://www.jstor.org/stable/20146835

Nash, S. 2010. Making Sense of Mount St. Helens. Bioscience [Internet], [cited 2010 Nov 3] 60(8), 571. Availiable from: Science Reference Center database: https://auth.lib.unc.edu/ezproxy_auth.php?url=http://search.ebscohost.com/login.aspx?direct=true&db=sch&AN=53450410&site=ehost-live&scope=site