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Title: Thinning shock and response to fertilizer less than expected in young Douglas-fir stand at Wind River Experimental Forest.

Author: DeBell, Dean S.; Harrington, Constance A.; Shumway, John.;

Date: 2002

Source: Res. Pap. PNW-RP-547. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 20 p

Publication Series: Research Paper (RP)

Description: Three thinning treatments (thinned to 3.7 by 3.7 m, thinned to 4.3 by 4.3 m, and an unthinned control treatment with nominal spacing averaging 2.6 by 2.6 m) were installed in a 10-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation growing on a low-quality site at the Wind River Experimental Forest in southwest Washington. Two years after thinning, two fertilizer treatments were superimposed on the design (0 and 224 kg per ha of nitrogen applied as ammonium nitrate). Diameter growth increased with increasing spacing throughout the 6-year study period, and it was also increased by fertilizer in both the thinned and unthinned (control) treatments. Thinning shock, a reduction in height growth after thinning, was expected at this study site because severe thinning shock had been documented in earlier nearby trials. Height growth was initially reduced slightly by thinning, but by the third 2-year period after thinning, height growth in thinned, unfertilized treatments was equal to or greater than height growth in the unthinned, unfertilized treatment. Fertilizer application increased height growth on average by 13 percent in the first 2 years after fertilization. In the third and fourth years after fertilization, however, fertilizer increased average height growth by 9 percent, but the increase was substantial (16 percent) only in the unthinned control treatment. The mild, ephemeral nature of thinning shock in our study was in contrast to the severe, long-lasting shock in earlier studies at Wind River. The milder shock in our study could be related to one or more of the following: (1) thinning was done at an early age, (2) impacts of fire (natural or prescribed) preceding planting were minor, and (3) seed source of the planted stock was appropriate for the location. Based on comparisons with other studies at Wind River and elsewhere, we suspect that use of nonlocal, maladapted seed sources in the earlier studies may have predisposed those trees to thinning shock. Furthermore, we suspect that the much higher responses to fertilizer application reported in the earlier studies may be associated with intense natural fires prior to planting, and the reduced nutritional status of those sites may have been further exacerbated by the use of maladapted seed sources.

Keywords: thinning, thinning shock, fertilization, nitrogen, seed source, fire, Wind River

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DeBell, Dean S.; Harrington, Constance A.; Shumway, John. 2002. Thinning shock and response to fertilizer less than expected in young Douglas-fir stand at Wind River Experimental Forest. Res. Pap. PNW-RP-547. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 20 p

 


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