### Description:

Using existing permanent research plot data, we developed equations
for predicting height-to-crown-base (HCB), 5-yr diametergrowth
rate (delta D), 5-yr height-growth rate (delta H), 5-yr mortality
rate (PM), and the maximum size-density trajectory for Douglasfir
and western hemlock in the coastal region of the Pacific
Northwest. With the exception of the HCB equation, the equations
developed for predicting trees from untreated plots agreed
in predictive behavior with previously published equations for the
study area. The HCB equation predicted shorter HCB (and therefore
longer crown lengths [CL]) than previously published equations
for the study area. Western hemlock showed no response to fertilization. Modifiers
for fertilization response were incorporated into the final equations
for predicting delta D, delta H, and PM in Douglas-fir. All three
modifiers for Douglas-fir predicted an increase in growth and
mortality rates with the amount of nitrogen applied and a decrease
with number of years since fertilization, with most of the
fertilization effect gone within 15 yr of application. For the delta D
and delta H modifiers, the size of the increase varied by the site index
(SI) of the plot, with plots of lower site quality showing greater
increases. For delta D, fertilization response did not appear to vary
by plot density, tree size, or tree position within the plot. Modifiers for thinning response were incorporated into the final
equations for predicting tree delta D for both species and delta H for
Douglas-fir. For both species, the delta D thinning-effects modifier
predicted an increased growth rate with the proportion of the BA
removed and a decrease with years since thinning; most of the
thinning effect was gone within 10 yr. For Douglas-fir, the delta H thinning-effects modifier predicted a reduced growth rate immediately
after thinning, with the size of the reduction increasing
with the intensity of thinning. Most of the reduction was gone
by about 10 yr.
For Douglas-fir, the combined effect on delta D and delta H of applying
both thinning and fertilization could be adequately characterized
by the product of the thinning modifier and the fertilization
modifier. The percent increase in predicted growth rate due to a
combined treatment thus was greater than the sum of the percent
increases for each treatment alone.
Analysis of the maximum size-density trajectory data strongly
suggests that plots of neither species approach a single maximum
stand density index value (SDI) as they develop. The potential
yield for a given site therefore depends, not only on its SI, but
also on its maximum SDI. Fertilization does not appear to affect
the intercept of the maximum size-density line for Douglas-fir. The strengths and weaknesses of the existing data sets and the
modeling and analytical approaches tested during development of
these equations are presented to aid future modelers, and alternative
modeling approaches are explored.