RELATIONSHIP BETWEEN SELF-FERTILITY, ALLOCATION OF GROWTH, AND INBREEDING DEPRESSION IN THREE CONIFEROUS SPECIES.

Abstract

Mortality and growth of self and outcross families of three wind-pollinated, mixed-mating, long-lived conifers, Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), and noble fir (Abies procera) were followed from outplanting to age 26 (25 for noble fir) in spaced plantings at a common test site. Response to inbreeding differed greatly among species over time and in all regards. Only Douglas-fir and noble fir will be contrasted here, because ponderosa pine usually was intermediate to the other two in its response to inbreeding. In earlier reports, compared to noble fir Douglas-fir had a higher rate of primary selfing and larger inbreeding depression in seed set. Douglas-fir continued to have higher inbreeding depression in nursery and early field survival. The species differed in time courses of inbreeding depression in height and in allocation of growth due to crowding. Between ages 6 and 12, the relative elongation rate (dm · dm-1 · yr-1 ) of Douglas-fir was significantly greater in the selfs than in the outcrosses. The response was not observed in noble fir. At final measurement, inbreeding depression in diameter relative to inbreeding depression in height was greater in Douglas-fir than in noble fir. At final measurement inbreeding depression in height was inversely related to inbreeding depression in survival. Cumulative inbreeding depressions from time of fertilization to final measurement were 0.98, 0.94, and 0.83 for Douglas-fir, ponderosa pine, and noble fir, respectively, which indicates that selfs will not contribute to the mature, reproductive populations.