Performance of improved genotypes of loblolly pine across different soils, climates, and silvicultural inputs

Deployment of improved loblolly pine (Pinus taeda L.) genotypes across the southern United States is a standard silvicultural practice. Most planting is conducted using open-pollinated (OP) families from first- or second-generation seed orchards, and these OP families typically display remarkable rank stability for productivity and quality traits across a range of site characteristics, climates, and silvicultural systems. With only a few exceptions, families are generally stable in performance across all sites within a climatic zone. As tree improvement and nursery programs progress towards deployment of more intensively selected genotypes and less genetically diverse full-sib families or clones, there may be a greater likelihood that genotype by environment (G × E) interactions will become important, particularly as the level of silvicultural treatment intensity increases. We present evidence from numerous trials with full-sib families and clones demonstrating that G × E for growth and other traits is no more significant than for OP families. At present and for the foreseeable future, G × E does not appear to be a major concern for the majority of deployed genetic sources under most silvicultural systems.