Genetic biodiversity impacts of silvicultural practices and phenotypic selection in white spruce

Forest-management practices relying on natural and/or artificial regenerati on and domestication can significantly affect genetic diversity. The aim of the present study was to determine and compare the genetic diversity of th e pristine old-growth, naturally and artificially regenerated and phenotypi cally selected white spruce, and to determine the genetic-diversity impacts of silvicultural practices. Genetic diversity was determined and compared for 51 random amplified polymorphic DNA (RAPD) loci for the adjacent natura l old-growth, naturally regenerated and planted white spruce stands at each of four sites, one oldest plantation and open-pollinated progeny of 30 phe notypic tree-improvement selections of white spruce from Saskatchewan. Each of the 420 white spruce individuals sampled was genetically unique. The ol d-growth stands had the highest, and the phenotypic selections the lowest, genetic diversity. The genetic diversity of the natural regeneration was co mparable to that of the old-growth, whereas the genetic diversity of the pl antations was comparable to that of the selections. On average, the genetic diversity of the old-growth and natural regeneration was significantly hig her than that of the plantations and selections. The mean percent of loci p olymorphic, the number of alleles per locust the effective number of allele s per locus, heterozygosity, and Shannon's index was 88.7, 83.8, 72.2 and 6 6.7; 1.89, 1.84, 1.72 and 1.67; 1.69, 1.62, 1.53 and 1.46; 0.381, 0.349, 0. 297 and 0.259; and 0.548, 0.506, 0.431 and 0.381 for the old-growth stands; natural regeneration; plantations; and open-pollinated progeny of selectio ns; respectively. Reduced genetic diversity in the plantations and selectio ns suggest that their genetic base is relatively narrow, and should therefo re be broadened in order to maintain genetic diversity, and sustainably man age and conserve white spruce genetic resources.