Effect of seedbeds on germination and survival of Douglas-fir Public Deposited
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Germination and survival of Douglas-fir on seedbeds of unburned, lightly burned, and severely burned soil, charcoal, litter, and sawdust, exposed to 100, 75, and 25 percent of full light, were studied on a south-facing clearcutting in the Coast range of Oregon. Irrespective of exposure to light, germination was best on charcoal and on severely burned soil, which was attributed to prolonged preservation of moisture at the surfaces of these materials. Differences in germination among these two and other seedbeds were statistically significant. The initial advantage of high germination on charcoal and severely burned soil was still apparent after six growing seasons. Stocking of trees remained highest on these seedbeds in spite of considerable mortality in the first growing season. Loss of seedlings was severe during, and shortly after, the period of germination. Then mortality decreased and became insignificant in following years. Rodents, heat, and damping-off, in this order, were the major causes of mortality. Heat was the predominant cause of mortality in the open, but rodents and damping-off fungi took the heaviest toll in shade. A preference of rodents for particular seedbeds was not apparent. To what extent mortality by heat and by damping off reflected influence of seedbeds could not be determined because of the confounding effect of rodents. Almost daily, temperatures of 1400 F (600 C) were maintained for 2-5 hours at the surface of seedbeds in the second half of the first growing season. Perhaps because of hardening of seedlings, mortality by heat decreased steadily in spite of increase in temperatures in the latter half of the season. Pronounced differences were not found in rate of depletion of moisture in the soil underneath various seedbeds. The supply of moisture became critically low only for a short period at the end of summer, apparently a consequence of absence of herbaceous vegetation. Growth in height of seedlings and development of their roots in the first year seemed to be unrelated to characteristics of seedbeds. Results of the present study are considered to be representative of initial development of Douglas-fir seedlings on south-facing clearcut areas in the Coast range of Oregon, provided germination occurs early and competing vegetation is absent.
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