ANALYSIS OF EARLY MORTALITY OF DOUGLAS-FIR SEEDLINGS IN POSTHARVEST PLANTINGS IN NORTHWESTERN CALIFORNIA

A life table study was conducted of injury and mortality of Douglas-fir seedlings in 44 plantations on public and private lands in Humboldt and Del Norte Counties, CA. Field examinations were made three times each year for the first 3 years following planting. Apparent and real mortalities were compiled in fife table format for nine time intervals. Seedling mortality per time interval in the different ownerships varied from 0 to 35.0% in real percentage terms, and totalled 14.0 to 70.7%. Highest mean mortality occurred in intervals 2 and 3 (late spring to fall, first year). Trend analyses, using a curvilinear regression model, showed significant differences in rates of mortality among ownerships. The performance of containerized and bareroot seedlings was very similar. Primary conclusions from the life table analyses, using a two-step modeling process, were (1) variations and covariations in mortality associated with intervals 2 and 3 were most important in determining total variation in survival in the 3-year period; intervals 1, 4, 7, and 9 also were critical in some instances; (2) planting- and weather-related factors were most important in intervals 14; disease, insects, and animals, alone and jointly, were more important in the second and third years; (3) substantial covariations in mortality among the time intervals indicated carryover effects; covariations among certain categories of causal factors indicated strong positive or negative interactions that either added to or dampened the direct effects of these factors.