Clonal growth in spire-shaped Engelmann spruce and subalpine fir trees

Abstract

The existence of multitrunk clusters in all-aged stands of spire-shaped Engelmann spruce and subalpine fir trees was documented and their origin was investigated using starch gel electrophoresis. Identical genotypes at nine variable loci demonstrated that most of the multitrunk clusters resulted from clonal growth of one individual. Significant differences in allele frequencies between clonal and nonclonal individuals in fir, but not spruce, suggest that there is a genetic component to clonal growth. Comparisons of sizes and ages among individuals with clonal growth and (or) sexual reproduction showed significant size and age differences, depending on mode of propagation, in spruce, and significant size differences in fir. In both species seed production was the predominant method of propagation and trees with seed production or seed production plus clonal growth were larger in size, but not necessarily older, than nonreproductive trees or those with clonal growth only. The fact that some trees had only clonal growth, some trees had only seed production, and some trees had both suggests that each type of propagation is advantageous under certain microenvironmental conditions. Results showing that it was impossible to determine visually if a given multitrunk cluster was composed of a single or multiple genets have implications for demographic and genetic studies in these and related conifer species.