Graduate Thesis Or Dissertation
 

A recent disturbance history of forest ecosystems at Mount Rainier National Park

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rr1721325

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  • An analysis was made of the recent catastrophic disturbance history of forests at Mount Rainier National Park. Basic data were tree ages from ring counts of increment cores taken from the early seral cohort, field mapping of age class boundaries and aerial photograph interpretation. Maps of present stand ages were constructed as a series of successive approximations after each field season. These maps illustrate the relationship among the major forest disturbers, fires, avalanches, and lahars (volcanic mudflows), and with topography. The forests are dominated by stands over 350 years old. Large stands (690 ha total) are over 1000 years old. South-facing slopes, especially high elevations, burn more frequently than protected north-facing slopes and streamside corridors. Fires are by far the most important major disturber, followed by snow avalanches and lahars. Fire frequency indices proposed by Heinselman (1973), Tande (1977) and Van Wagner (1978) were compared and found to poorly describe fire frequency at Mount Rainier, partly due to the natural regime of infrequent, catastrophic fire. Natural fire rotation was found to be 434 years and 306 years using Heinselman's and Van Wagner's index, respectively. Episodes of major fire also correspond well with major droughts reconstructed for locations east of the Cascade crest by Keen (1937) and Biasing and Fritts (1976). Only two major fires since 1300 AD do not correspond to a major drought reconstructed by either of these investigators. Of the eight major droughts from Keen (1937) only two lack a corresponding large fire at Mount Rainier. Modern man's impacts on the disturbance regime have been relatively slight, perhaps involving an increase in fire frequency during the 1850 to 1900 period followed by a decrease in fire frequency since 1900. No unnatural fire frequency or fuel build-up patterns have occurred, since fires are relatively infrequent and fuel build-ups high. Since fire plays an important natural role in maintaining the forest mosaics at Mount Rainier, it should be included as a basic natural agent in the Park's management. Both fires, especially during prolonged droughts, and lahars are potentially very destructive. Given the long natural interval between major fires, there is some lee-way in a time schedule for fire management.
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