Graduate Thesis Or Dissertation
 

Comparative development of a thinned and a natural Douglas-fir stand from 45 to 60 years of age

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  • 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.
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