The Effect of Certain Site and Soil Factors on the Establishment of Douglas-Fir on the Tillamook Burn
1955
Lowry, G. L. | Youngberg, C. T.
This paper presents a preliminary report of studies dealing with soil moisture-seedling survival relationships conducted on the Tillamook Burn in northwestern Oregon during 1953. Ten one-fifth acre plots were selected from the current years planting program. Survival was calculated on the basis of total trees planted. Factors investigated include: Percent slope, aspect, soil texture, structure, depth, organic matter content, and range of available moisture. Weather data were obtained from nearby lookouts. Soil moisture determinations were made weekly throughout the summer period. Although there were not sufficient plots to establish statistical significance, certain factors were found to be affecting survival. Among these were aspect, percent slope, and soil texture. Southerly aspects coupled with coarse textured soils and slopes greater than 40% showed the highest mortality. On the other hand, northerly aspects, loam and silt loam textures and slopes less than 40% had excellent survival. Between these two extremes various gradations existed. In all cases where high mortality occurred, soils had been depleted of available moisture (below 15 atm.) for periods approaching 30 days.
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