Genetic improvement effects on growth and yield of loblolly pine plantations
A series of hypotheses concerning stand dynamics and growth patterns in loblolly pine plantations of improved stock relative to plantations of unimproved stock were developed and tested. Results of these tests indicated that at the seed source and family levels: (1) the shape of the height-age curve is influenced by the site, but the level of the height-age curve is influenced by the seed source or family; (2) at the seed source and family levels, the shape of the height-diameter relationship at a given age is influenced by the site and by the initial density; and (3) the level of the height-diameter relationship is affected by the seed source or family and is directly related to the dominant height of the seed source or family at that age. Indications are that by choosing the height curve carefully, differences in development among seed sources and families on a given site can be modeled by altering the level of the height-age curve. Data from temporary plots in stands planted operationally with genetically improved stock were used to test for differences in stem quality and volume relationships as compared to comparable plots from unimproved plantations. Stem quality in the improved stands was not substantially different than in unimproved stands in the same region and of the same age range. There was no difference in stem taper or individual tree volume between improved and unimproved stock. Yield equations, based on the independent variables age, average height of dominants and codominants, and surviving number of trees, were fitted to these same plot data from operationally planted improved and unimproved stands. There were no significant differences in the yield equations, indicating that a single yield equation should suffice when the independent variables are correctly specified. For. Sci. 33(3):707-724.