Dynamics of improved loblolly pine plantations and the implications for modeling growth of improved stands
A study was initiated to examine the dynamics of genetically improved loblolly pine plantations and to develop guidelines for Incorporating the effects of genetic Improvement Into various types of growth and yield models for loblolly pine plantations. The limited data base from stands of Improved stock d lctated that any model Ing effort concentrate on the synthesis of fragmented Information from many types of studies rather than the usual data fitting procedures. A series of hypotheses concerning stand dynamics and growth patterns In stands of Improved stock relative to stands of unimproved stock were developed and tested. Results of these tests indicate: 1) at the seed source and family levels, the shape of the height-age curve is dictated by the site, but the level of the height-age curve is dictated 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 determined by site and initial density while the level of the height-diameter relationship Is determined by the seed source or family and ls directly related to the dominant height of the se.ed source or family at that age; and 3) given that s1lv1cultural treatments are the same and are equally intense and successful, variances of height and diameter in stands originating from selected genotypes are not different from those in genetically unimproved stands. Implications for modeling growth of stands originating from selected genotypes are: 1) genetic improvement affects the rate at which stands develop, but does ·not fundamentally alter the pattern of stand development from that of unimproved stands; 2) changes in genetic material on a given site will likely affect the level, but not the shape, of such basic relationships as the height-age and height-diameter relationships; and 3) correctly characterizing the height-age profile will be very important.