Genetic implications in the decline of red spruce

Abstract

Despite substantial increases in atmospheric pollution and significant correlations between specific inputs and red spruce (Picea rubens Sarg.) decline at certain locations in eastern North America, it has not been possible to demonstrate a consistent relationship between severity of decline and either pollution inputs or climatic factors throughout the region of decline. These results indicate that different pollutants or environmental features may be associated with red spruce deterioration in different regions and raise the question of why red spruce, and not other sympatric species, might be predisposed to injury from a diversity of inputs and over a large geographic area. In this paper we present data to indicate red spruce is a relatively uniform species genetically, and we discuss the possibility that it may be deteriorating because it lacks the genetic flexibility to cope with and respond to abrupt environmental modification. Estimates of genetic variability in red spruce were determined from electrophoretic assessments of 30 trees from each of 10 populations distributed throughout the region of red spruce decline. An examination of genetic variation at 36 loci revealed an average observed heterozygosity for red spruce of 6.9% with only 21.3% polymorphic loci and 1.43 alleles per locus. These genetic variability estimates are considerably lower than those reported for other north-temperate woody plant species, including conifer species that are sympatric with red spruce and are presumably exposed to similar selection pressures. In one population, individual trees that were high in observed heterozygosity were generally more vigorous (as estimated from sapwood area/basal area ratios) than less genetically variable individuals. As a result, it appears highly heterozygous individuals may be more resilient and capable of surviving and reconstituting viable populations in the future. We discuss five additional lines of evidence that are consistent with a hypothesis of insufficient genetic variability and limited adaptability in red spruce.