Postdispersal Selection Following Mixed Mating Ineucalyptus Regnans

Eucalyptus regnans is a mass flowering, tall forest tree of southeastern Australia with a mixed mating system. A field trial containing randomized single tree plots of self, outcross, and naturally open-pollinated (OP) progenies of 13 parents from two natural populations was surveyed over 15 yr. Inbreeding depression in survival at 15 years was 67% for selfs, one of the highest levels reported for a tree species, and differed little between populations. OP progenies were intermediate and the difference in fitness among the three cross types indicated that at planting, 59% were derived from outcrossing. However, with selection against the inbred progenies, this increased to 83% by 15 yr of age. Most selection against selfs occurred after four years, coincident with canopy closure and the apparent onset of intense competition.