Inbreeding Depression in Height, Height Growth, and Survival of Douglas-fir, Ponderosa Pine, and Noble Fir to 10 Years of Age

Abstract

Abstract Self-, outcross-, and wind-pollination progenies of Douglas-fir, ponderosa pine, and noble fir were measured at outplanting and annually to age 10 years. Inbreeding depression in survival the first 2 years in the plantation ranged from 3 to 16 percent, and thence to age 10 years ranged from 0.4 to 3 percent. Inbreeding depression in plant height ranged from 24 to 30 percent at outplanting and ranged from 29 to 36 percent at age 10. Gompertz growth curves were fitted to annum height measurements and elongation rates, based on the curves, determined for ages 5 and 9 years and for a common height. Average inbreeding depressions in elongation rates (growth in centimeters/year) were 35 percent (age 5), 28 percent (age 9), but only 10 percent when adjusted to a common height. The interpretation was that relative inbreeding depression at any age consists of a genetic inbreeding depression of growth rate and an additional effect resulting from self and outcross plants being at different points on a more or less common growth curve. Losses in productivity of wind-pollinated Douglas-fir and ponderosa pine plantations at age 10 were estimated based on observed inbreeding depressions in survival and height and on expected frequencies of self seedlings in the wind-pollination populations. Losses were estimated to be about 5 percent in Douglas-fir and about 8 percent in ponderosa pine. Forest Sci. 28:283-292.