Graduate Thesis Or Dissertation

 

Spatial and developmental patterns of the vegetation of Black Butte, Oregon Pubblico Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6h440w16g

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  • Black Butte presents a unique natural laboratory for ecological study. It is a volcanic cone of uniform configuration located in the rain shadow on the east flank of the Oregon Cascades. Soils are of very recent origin with no obvious development of horizons. Physical and chemical analysis revealed little dissimilarity within the study area. However, fire has played an important ecological role. Dendrochronological analysis of cross sections of mature Pinus ponderosa revealed repeated widespread burning at an average interval of 12.3 years for the years 1830 to 1903. The Forest Service has practiced fire exclusion since that time. The vegetation of the lower :slopes is dominated by mature Pinus ponderosa. Libocedrus decurrens, Pseudotsuga menziesii, Abies grandis, Pinus albicaujis, and Abies lasiocarpa become successively more abundant at progressively higher elevations. Tree, shrub and herb data were gathered via the point centered quarter method at 1000 foot elevation intervals along eight transects radiating from the summit. In subsequent analysis, designed along the lines of a continuum analysis, it was possible to demonstrate via relative importance values that some species gradually give way to other species along environmental gradients. However, considerations of the age class patterns of mixed stands revealed that they are not stable and therefore with freedom from disturbance by fire or other catastrophe will come to be less heterogeneous in overstory composition. In most instances, this will be at the expense of Pinus ponderosa which, due to its superior resistance to fire, has been able to occupy and thrive in habitats considerably more mesic than its true habitat type. After 60 years of fire exclusion, species of greater shade tolerance and with generally higher moisture requirements are now responding with relatively greater reproduction than Pinus ponderosa on these mesic sites. These patterns of reproduction allow one to project to six climax associations which will come to occupy six different habitat types. Due to the uniformity of soil and topography within climatic climax zones, these may be interpreted theoretically as encompassing single habitat types with variation in seres being due to rate of succession following fire. These distributional patterns are very similar to those described by other workers for the east slope of the Cascades. However, due to the relatively xeric conditions of Black Butte, equivalent types occur at approximately 500 feet higher elevation.
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