The procedure of forest level harvest scheduling
incorporates many inputs of an uncertain nature. Forest
management planners must be aware of the possible effects of
the use of erroneous input information on the results of
their planning. With that knowledge they can better plan a
risk management strategy and make appropriate adjustments in
assumptions or recommendations.
Two of the most important uncertain input elements are
future yield predictions and initial inventory information.
The objective of this study was to identify the size of
effects on harvest schedules of using uncertain yield and
inventory data, specifically for Douglas-fir of the Pacific
Northwest. To do this sensitivity analysis, harvest
schedules were developed using the sequential even-flow
option of the TREES simulation model (Tedder et al. 1980)
with a ceteris paribus format where all was held constant except the yield predictions or the initial inventory data.
Several different yield models have been developed for
predicting future yields of Douglas-fir. For extensive
management, this study compares four plus an arbitrary
adjustment of one of the four in a harvest scheduling
context; hypothesizing that there should not be any
meaningful differences in harvest schedules developed when
using the different yields. The tested yields included
Bulletin 201 (McArdle et al. 1930) , DFIT (Bruce et al. 1977,
Reukema, Bruce 1977), DNR Empirical Yields (Chambers, Wilson
1972), Hoyer's Natural Stand Yields (Hoyer 1975), and
Bulletin 201 less 15 percent. Bulletin 201 as modified by
Beuter et al. (1976) , DFIT, and modified Bulletin 201 less
15 percent were tested for intensive management.
Eight sample inventories were obtained that represent a
spectrum of site class and initial structure. Each
inventory is adjusted twice to make a total of 24 different
inventories which are combined with the yield information to
generate the harvest schedules. Relative differences in
percent are reported with emphasis on first decade, last
decade, and total planning horizon differences
