Graduate Thesis Or Dissertation
 

Interacting effects of stand density, site factors, and nutrients on productivity and productive efficiency of Douglas-fir plantations in the Oregon Cascades

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5138jh10r

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  • The objectives of this research were to study: a) the effect of thinning and treatments consisting of pruning and multinutrient fertilization on aboveground biolnass increment, growth efficiency (GE), and foliar nutrients; b) the influence of topoedaphic variables (soil nutrients, slope, aspect, and rock content) and foliar nutrients on both leaf area increment and GE; and c) the influence of topoedaphic variables on the rate of iiJneralizable N. Studies were conducted in young Douglas-fir plantations in the western Cascades of Oregon. Net aboveground biomass increment over a 6-year period averaged 14.5, 7.8, and 5.5 Mgha-1.yr-1 for unthinned, noderately thinned, and heavily thinned stands, respectively. Aboveground biornass increment and GE were analyzed in three 2-year periods. Density affected aboveground biomass increment in all periods, and there was an increasingly significant treatment effect in each period, but no significant interaction between stocking density and treatment. Stand density had the major effect on GE, but there was also a significant interaction between stocking density and treatment during the 1985-'87 period. Foliar analysis indicated that thinning improved N, K, and Mg nutrition, and resulted in increased translocation of K from one-year old to current year foliage. Multivariate and regression analyses suggest that relative leaf area increment is correlated most closely with one or another measure of Mg, K, and N availability, whereas GE correlates most strongly with leaf area index, mineralizable N, and foliar Mg content. Mineralizable N in two soil depths did not vary significantly by stocking density, treatment, or density-treatment interaction. The rate of mineralizable nitrogen expressed as concentration basis averaged 49 per cent lower at the 20-40 cm depth than at the 0-20 cm depth. Mineralizable N expressed on an area basis correlated positively with total soil N, exchangeable Ca, and adjusted aspect, and negatively with rock content and slope steepness.
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