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Effects of regeneration dynamics on predicted development of interior Douglas-Fir stands Lencar, Cornel Cailin

Abstract

The presence of natural regeneration and its abundance has a tremendous impact on the future development of forest stands. The relationship between the overstory and the understory in partially cut stands in the Interior Douglas Fir dk1, dk2 and dk3 subzone variants of the British Columbia (BC) biogeoclimatic ecosystem classification system (BEC) was studied through different analytical methods using data collected in the summer of 1999. The data were collected to calibrate the small tree height growth and regeneration components of PrognosisBC growth and yield model in the vicinity of Kamloops and Williams Lake, BC. A total of 335 plots distributed in three ecological zones, across a range of time-since-disturbance, site and topographical characteristics were sampled. One of the objectives of this study was to develop equations for predicting small tree height growth within PrognosisBC. Several equations were tried. The equation selected contained the same basic stand attributes used in the Northern Idaho [NI] version of Prognosis; however, in the modelling process, other density and structural indices were found to be significant. A second objective was to study the relationship between the regeneration abundance and overstory, and between the regeneration and other site attributes. Several analytical methods were employed. Stands were classified using basic criteria such as species composition, residual basal area, and site type in an effort to characterize stand attributes. Average levels of regeneration were calculated for each subzone and grouped by residual basal area and site conditions to form a stand matrix. Stands disturbed more than 10 years ago were selected from each group of sampled stands defined in the matrix and tree lists were obtained. For each sampled stand, different levels of regeneration and silvicultural treatments were used as input to the PrognosisBC model. These stands were then projected for 40 years and compared across regeneration levels. Little difference was found for the total predicted volumes among the different levels of input regeneration. However, there were considerable differences in the predicted stand structures associated with the different regeneration assumptions. Species composition and stand structures varied among subzones and moisture levels, but trends in regeneration amount and composition were repeated across the subzones.

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