Graduate Thesis Or Dissertation
 

Amount and chemical composition of understory vegetation in Alsea basin forest communities

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bn9999139

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  • The understory vegetation was sampled in eight plant communities of a Douglas-fir ecosystem to determine the organic matter production and mineral composition. Four sample sites were selected in each plant community and the understory vegetation sampled using the method of quadrats of successively increasing size. All herbaceous plants were separated by species while shrubs were first separated by species and then, for each species, by leaves or needles and woody parts. The samples were immediately weighed to obtain the green weight and then were taken to the laboratory, dried, and re-weighed to obtain the dry weight of organic matter produced. After suitable preparation the samples were analyzed chemically to determine their nitrogen, phosphorus, potassium, calcium, magnesium, and manganese concentrations. Using the amount of dry organic matter produced (in kg. /ha.) and the mineral concentrations (in %), the percentage concentrations of these nutrients were converted to the kilogram per hectare basis. It appeared that the organic matter production and mineral content of understory vegetation varied significantly between plant communities. In other words, organic matter production and mineral content tended to be characteristic of each plant community. It was found, however, that unstable, immature communities showed a greater variation in total organic matter production than did climax communities. It was further found that, considering a limited area, the organic matter production of different sample sites within a community was similar. One of the limiting factors for organic matter production, as well as for total mineral content, of understory vegetation was light intensity at ground level as indicated by the percentage crown cover. The mineral concentration of the shrub layer was found to be lower than that of the herb layer with the exception of manganese, for which the shrubs had a higher concentration than did the herbs. It was also noted that certain plant species appeared to be selective for certain minerals. The results of this investigation seem to indicate that the understory plays a very important role in the nutrient cycle. Although it contributes a smaller amount of organic matter than does the overstory, the under story has a much higher mineral concentration and its annual turnover appears to be a very important factor in determining the fertility level of the forest floor.
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