Abstract:
Clearcutting is a sound silvicultural practice when exercised
in the proper environmental location. Foresters have learned through
bitter experience that clearcutting Douglas-fir forests, located on
droughty south-facing slopes, often leaves uncorrectable regeneration
problems. Thousands of acres of unproductive grass and brush throughout
the Douglas-fir region are unavoidable reminders of inappropriate
sites for clearcutting.
Underplanting, as demonstrated in this study, is an alternative
to regeneration problems commonly associated with clearcutting
in arid portions of the Douglas-fir region. This technique of planting
Douglas-fir seedlings under the overstory of a mature Douglas-fir
forest before removal of the entire canopy, was tested in the dry,
arid portion of the interior Coast Range near Corvallis, Oregon. On
a typically droughty south-slope, consisting of an old growth stand,
a recently thinned Douglas-fir stand, and an old unsuccessfully regenerated
clearcut, 1200 seedlings were planted.
An attempt was made to evaluate survival as a function of
three parameters: light, moisture stress, and vegetative competition.
Ozalid light integrators measured light at each seedling on the
forest floor. Seedling moisture stress was evaluated with a pressure
bomb, while a measure of vegetative cover surrounding each tree indicated
competition.
Contrary to generally recognized supposition, this study indicates
that Douglas-fir seedlings can survive, become established, and
grow in the shade of a mature forest. After one growing season, survival,
was highest in the old growth stand with 614 percent, and lowest
in the clearcut with 38 percent. In addition, Douglas-fir does not
require full sunlight for survival Less than 30 percent of full sunlight
provides the best survival conditions.
Further experiments will be conducted to investigate survival
at the end of two growing seasons and ultimately test seedling response
when the overstory is removed.
