Abstract:
An understanding of the dynamics of individual tree and stand
growth, development, and structural patterns during the immature
formative years of a commercial species is essential to determine
correct thinning practices necessary to attain desired objectives.
This study compared a natural, medium-site Douglas-fir stand
and an adjacent similar stand released by a severe crown thinning
in 1955 at 45 years of age. Individual tree measurement and classification
data collected in 1955 and in 1970 from all stems 1.5 inches
and larger on permanent one-acre research plots within each stand
were used to compare growth and developmental changes occurring
during the interval. In addition, the Douglas-fir on both plots were
measured in 1970 with a Barr and Stroud optical dendrometer to
determine volumetric and morphological differences.
The interplot and intraplot characteristics manifested during
and at the end of the 15-year period on each study area were examined.
Structural changes of crown classes and components were
delineated and investigated. Regression analyses were performed
to compare basal area growth rates and volume similarities or
differences by crown classes within and between the plots.
After 15 years, the thinned stand was superior in site index,
stand restructuring for dominance, basal area growth, and d.b.h.-
volume relationships based on total cubic foot volume inside bark.
Neither the ratio of live crown length to total height nor defect
due to crown breakage and resulting Fomes cajanderi had an influence
on subsequent crown class movement or basal area growth rate.
Mortality was caused by suppression, and occurred in the
intermediate and overtopped crown classes.
The dynamics and magnitude of crown class movement, especially
stability in the dominant class and the proportion of upward
movement by the intermediate and codominant classes were greater
than previously observed in other studies. This phenomenon has a
major impact on silvicultural decisions, and warrants further intensive
investigation. Intermediate trees showed the greatest vertical
crown class movement; overtopped trees were candidates for mortality
in the near future.
The greatest actual basal area growth on an individual tree basis occurred in the dominant class on the thinned plot, but the
larger codominants and the smaller dominants from the same plot
exhibited superior potential for response to release with proportionally
larger basal area increases. All crown classes except overtopped
on the thinned study area were capable o relatively greater
basal area growth than their unthinned counterparts.
Fifteen years after release, the volumes of the dominant and
codominant trees on the thinned area were significantly greater than
the dominants and codominants of corresponding d.b.h.s on the
unthinned plot. The d.b.h., height, crown length, and crown surface
area were also substantially greater in these crown classes
on the thinned plot.
At 60 years of age, both plots were forming into three crown
classes--a dominant, a codominant, and an intermediate-overtopped
group based on crown class structure, basal area growth, and volume
characteristics. The thinned stand, however, had relatively superior
characteristics in these categories.
The need for intensive periodic remeasurement of single-tree
plots to determine the effects of genetics, tree physiology, microsite,
and the spatial-distribution relationship on growth and development
is discussed.
