Genetic variation in competitive ability of some shade-tolerant and shade-intolerant Pacific Coast (USA) conifers*

Malavasi, U.C. and Perry, D.A., 1993. Genetic variation in competitive ability of some shade-tolerant and shade-intolerant Pacific Coast (USA) conifers. For. Ecol. Manage., 56:69-81. Variability in growth response to stocking density and neighbor composition was compared among half-sibling families of four tree species representing two pairs of shade-tolerant and shade-intolerant species, each pair from the same life zone. The hypothesis was that the wider regeneration niche of shade-tolerant species, which establish both in disturbed areas and within closed forests, would produce greater genetic variability among families than occurs in shade-intolerant species, which establish primarily in disturbed areas. Families of western hemlock (Tsuga heterophylla (Raf.) Sarg.), coast Douglas fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) and Pacific silver fir (Abies amabilis (Dougl.) Forbes) varied in their responses to stocking density, but those of noble fir (A. procera Rehd. ) did not. As hypothesized, shade-tolerant species were significantly more variable than shade-intolerant ones, a result consistent with electrophoretic studies of shade-tolerant and -intolerant plants and supportive of the hypothesis that at least a portion of genetic variability contained within populations represents adaptation to variable environments.