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Patterns of Biotic and Abiotic Factors of Succession Following Debris Flows at Mount Rainier National Park

The frequency of debris flows on Mount Rainier is increasing due to glacial retreat as a result of climate change. The intent of this investigation was to study biotic and abiotic factors of succession that are indicators of the age of debris flows in order to understand the history of debris flows that have occurred on Mount Rainier and better predict the effects of climate change. Factors were selected based on their low level of impact on the environment and being easily observable in the field. Data was collected from two debris flow prone valleys and a control section in Mount Rainier National Park during the months of October and July. Variations in O-Horizon depth, canopy coverage, soil color, soil pH level and lowest branch height were observed utilizing belt and line transects. Mathematical models were constructed for each factor to identify the factors that change over time that might be useful in predicting the age of debris flows. O-Horizon depth and canopy coverage were selected for further investigation because they are interconnected factors, display clear trends and have high R2 values (above 90%). Using the equations for the regression curves predictions were made for three previously untested sites of known ages based on the logarithmic curves. Additional data was then collected at these sites utilizing the same field methods. While canopy coverage was not found to be a reliable predictor of debris flow age, O-Horizon depth as a model was further validated. Introduction On November 6th and 7th, 2006 record rainfall and snow melt combined to form debris flows, flooding and erosion that devastated both natural and recreational areas within Mount Rainier National Park. As a result, the park was closed for six months, the longest period of time of closure since World War II. It took the combined efforts of 1,500 volunteers and approximately thirty million dollars to reopen the park; however some areas remain unoperational and inaccessible and surrounding businesses reliant on tourism have yet to fully recover1. Many aspects of this disaster are indicative of the degenerative effects of climate change that have been impacting mountainous regions in recent years. Although these heavy damages were devastating, they pale in comparison to what lies ahead as global climate change pervades and Mount Rainier’s massive glaciers continue to retreat, shedding their once frozen bodies, leading to destruction in the valleys below2. The purpose of this investigation is to study the stages of succession following debris flows in order to better determine the age of debris flows that have occurred in Mount Rainier National Park. By doing so, a historical record of Patterns of Biotic and Abiotic Factors of Succession Following Debris Flows at Mount Rainier National Park Laura Kostad1* and Denise Thompson2 Student1, Teacher2: Orting High School, Orting, Washington 98360 *Corresponding author: laurakostad@hotmail.com IN SCHOOL ARTICLE debris flows that have occurred in the area can be compiled to assist scientists and park personnel in planning for the protection of natural and historical resources as the park responds to the rapidly increasing effects of global climate change. Furthermore, by gaining this understanding they could more accurately address the matters of intervention, observation and estimation so as to know what to expect in the following years as the ecosystems regenerate3,4. A debris flow is a slurry of mud and rock mixed with water that resembles concrete tumbling downslope destroying all vegetation within its path either by knocking it down or burying it. Debris flows can result from volcanic activity or as glaciers warm and retreat, due to rising temperatures. These retreating glaciers uncover sediments that provide the solid materials for debris flows. When an excess of water from a major rain storm, melting glaciers, or snowmelt flows over these exposed sediments, it carries them destructively downstream picking up more and more debris from the valley floor. As the valley slope decreases, the debris flow slows down eventually depositing meters of sediment in the streambed. Because of global climate change, debris flows are increasing in frequency in many glacial occupied valleys on Mount Rainier2,3,5,6. The relationship existing between the amount of canopy coverage observed in a particular site and the age of a debris flow is in general that the greater the percentage of canopy coverage, the farther along the ecosystem is in terms of succession because, for example, in a climax community (the apex of succession), canopy coverage is nearly one hundred percent due to old growth coniferous trees which dominate the forest canopy and that are only present when an ecosystem has reached this point in succession. However, pioneer species such as Alder quickly colonize debris flow surfaces resulting in a narrow window of time (potentially 15-20 years) for which canopy cover would be useful as a predictor. Vegetative destruction caused by debris flows leads to forest succession. Debris flows are considered to be a form of high level disturbance because they decimate nearly all of the vegetation in an environment and bury the soil layer under meters of sediment. When this layer is absent, an ecosystem is considered to be in primary succession. Secondary succession is regrowth in an area that retains its soil layer. When a debris flow occurs, the affected ecosystem essentially has to start over from scratch and recolonize completely starting with making a new soil layer. This is dangerous for ecosystems because rather than encouraging biodiversity, ecosystems with frequent debris flows never reach the climax community stage. Furthermore, the more biodiversity in an ecosystem, the more stable the ecosystem will