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Abstract: Studies were made in 25 Douglas fir stands in Washington and Oregon and in 16
western hemlock stands in Washington. Site index, total and mineralizable soil N were the only
variables correlated with growth response to N fertilizer by Douglas fir. Growth response of
hemlock was correlated with extractable P/total N in the soil. Total N and mineralizable S in
mineral soil were highly correlated and showed moderate negative correlations with growth
response of hemlock, but site index was not correlated with response. Results suggest that site
index and soil N seem promising indicators of the response of Douglas fir to N fertilizer, while
extractable P and the P/N ratio may indicate the response of hemlock. Soil N appears to be more
important than soil P in predicting the response of Douglas fir on the sites studied. Soil S did not
appear to limit the response of either species to N fertilizer and does not seem promising for
estimating the response to N.
488. Radwan, M.A., J.S. Shumway, D.S. DeBell and J.M. Kraft. 1991. Variance in response of polesize
trees and seedlings of Douglas-fir and western hemlock to nitrogen and phosphorus
fertilizers. Canadian-Journal-of-Forest-Research 21(10): 1431-1438.
Keywords: nursery operations
nursery fertilization
fertilization
tree physiology
growth
Abstract: A study was made of the effects of N, P and NP fertilizer treatments on plant
nutrients and growth of Douglas fir (Pseudotsuga menziesii) and western hemlock (Tsuga
heterophylla). Three trials were conducted, (1) and (2) on pole-size trees at two different sites in
Washington and (3) on potted seedlings in a lathhouse; only T. heterophylla was studied in (2).
Soil series were Bunker for Douglas fir and Klone for western hemlock in trials 1 and 3, and
Vesta in trial 2. Nitrogen fertilizers used were urea in trial 1 and ammonium nitrate in the other
two trials; P was applied as triple superphosphate in all three trials. For each species in trial (1), P
was applied at 0, 100, 300 and 500 kg P/ha and N was applied at 0 and 224 kg N/ha in a factorial
design. In trial (2), P was applied at 0, 100 and 300 kg P/ha and N was applied at 0 and 112 kg
N/ha in a factorial design. In trial (3), N and P were applied individually to seedlings at a rate of
100 kg N/ha and 226 kg P/ha. In general, fertilizer treatments changed the levels of some planttissue
nutrients of the pole-size trees and potted seedlings. Neither height nor basal area growth of
the trees were significantly affected by any of the treatments in the first two trials. Seedling
growth of both Douglas fir and western hemlock was improved by P fertilizer, but was negatively
affected by N fertilizer. The results clearly show differences between pole-size trees and
seedlings in response to N and P fertilizers. It is concluded that N should not be applied where
soils are high in N and low in P, and that P applications should be confined to sites with low-P
soils, when trees are young, before canopy closure.
489. Ralston, R., J. Buongiorno and J.S. Fried. 2004. Potential yield, return, and tree diversity of
managed, uneven-aged Douglas-fir stands. Silva-Fennica 38(1): 55-70.
Keywords: thinning
commercial thinning
economics
yield
Abstract: The effects of different management regimes on uneven-aged Douglas-fir stands
in the Pacific Northwest of the United States were predicted with a simulation model.