Abstract:
Commercial thinnings in a 50-year-old stand of nearly pure,
well stocked, even-aged western hemlock (Tsuga heterophylla) on the
Hemlock Experimental Forest near Hoquiam, Washington, began in
1952 and ended in 1968. The experiment consisted of two replications
of four different thinning treatments, high and low thinning, both at
frequent and infrequent intervals. Volumes removed in thinning ranged
from 41 to 107 percent of the gross cubic volume increment for the
experiment. Field layout of the experiment and methods of analyses
are discussed in detail.
All thinned treatments had a higher growth percent than their
respective control areas. Thinning also indicated distinct improvements
in average diameter increment and realized increment, which
is the volume harvested in thinning plus the volume added to the growing
stock. Gross growth and mortality were not greatly affected by
thinning. Although thinning in general produced positive results, no
single type of thinning treatment could be isolated as the 'best' method.
