IntensIve sIlvIculture - Forest Science Labs - Research Network ...

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areas, but were not significantly different from the untreated control 3 yr after treatment. Slashing
of sclerophyll brush to release long-suppressed Douglas fir is not recommended because of rapid
brush recovery by sprouting.
272. Homann, P.S., B.A. Caldwell, H.N. Chappell, P. Sollins and C.W. Swanston. 2001. Douglas-fir
soil C and N properties a decade after termination of urea fertilization. Canadian-Journal-of-
Forest-Research 31(12): 2225-2236.
Keywords: fertilization
soil properties
Abstract: Chemical and microbial soil properties were assessed in paired unfertilized and
urea fertilized (>89 g N/m-2) plots in 13 second-growth Douglas fir (Pseudotsuga menziesii)
stands distributed throughout western Washington and Oregon, USA. A decade following the
termination of fertilizer application, fertilized plots averaged 28% higher total N in the O layer
than unfertilized plots, 24% higher total N in surface (0-5 cm) mineral soil, and up to four times
the amount of extractable ammonium and nitrate. Decreased pH (0.2 pH units) caused by
fertilizer application may have been due to nitrification or enhanced cation uptake. In some soil
layers, fertilizer application decreased cellulase activity and soil respiration but increased wood
decomposition. There was no effect of fertilizer application on concentrations of light and heavy
fractions, labile carbohydrates, and phosphatase [phosphoric monoester hydrolases] and xylanase
activities. No increase in soil organic C was detected, although variability precluded observing an
increase of less than ~15%. Lack of a regionwide fertilizer application influence on soil organic C
contrasts with several site-specific forest and agricultural studies that have shown C increases
resulting from fertilizer application. Overall, the results indicate a substantial residual influence
on soil N a decade after urea fertilizer application but much more limited influence on soil C
processes and pools.
273. Hong, S. and J.J. Morrell. 1997. Treatability of Douglas-fir heartwood with ACZA or CCA:
effect on site, silvicultural practice, and wood properties. Forest-Products-Journal 47(10): 51-55.
Keywords: planting operations
fertilization
thinning
wood quality
Abstract: The effects of site, silvicultural treatments, and wood properties on treatability of
Douglas-fir (Pseudotsuga menziesii) heartwood, from Washington and Oregon, with chromated
copper arsenate (CCA) or ammoniacal copper zinc arsenate (ACZA) were studied. Thinning
appeared to be associated with slight improvements in treatability (penetration and retention of
preservative), but combinations of thinning and fertilization had no significant effect on this
property. Other factors such as site, height from which the sample was removed, and percentage
of juvenile wood had inconsistent effects on treatability. Although the results indicate that
silvicultural practices have minimal effects on treatability of Douglas-fir, further studies are
required to clarify these effects.
274. Hopmans, P. and H.N. Chappell. 1994. Growth response of young, thinned Douglas-fir stands to
nitrogen fertilizer in relation to soil properties and tree nutrition. Canadian-Journal-of-Forest-
Research 24(8): 1684-1688.
Keywords: fertilization