Will crown ideotype help determine optimum varietal silviculture?This article is part of a larger document. View the larger document here.
Recent advances in somatic embryogenesis permit large numbers of clonal loblolly pine (Pinus taeda L.) to be produced and deployed. Clones may have greater growth (mean annual increment exceeding 30 cubic meters per hectare per year), greater stand uniformity and may be more susceptible to genotype by environment interactions when they are deployed in intensively managed plantations. Consequently, large numbers of clones will need testing under a range of silvicultural treatments to effectively and efficiently identify those that are best for deployment. Crown ideotypes are described by their crown dimensions, where the crop ideotype has tall (long live crown length) and narrow (short branch length) crowns and the competition ideotype has short (short live crown) and wide (long branch length) crowns. We tested the hypothesis that the response to silvicultural input was not related to crown dimension in a study in the Virginia Piedmont where six genetic entries (four clones, one mass control pollinated family and one open pollinated family) were planted at three initial stocking levels (617, 1235, and 1852 stems per hectare) and two levels of silvicultural input (low, i.e., similar to typical operations, and high, where nutrient limitations were eliminated). After three years of growth, significant silviculture and genetic entry effects were observed for diameter, height, live crown length, crown width, crown volume and stem volume increment, where silviculture increased these variables for all genetic entries although the increase due to silviculture was not consistent across genetic entry (genetic entry by silviculture interaction). The stem volume growth response to silvicultural treatment decreased with increasing crown volume. Crown ideotype may be useful in determining the response of clonal material to silvicultural input. However, it is important to know the conditions under which the ideotype is determined to be able to successfully use this method to predict the response to silvicultural input.