Indirect genetic selection for early growth and disease resistance of southern pines has
proven remarkably successful over the past several decades. However, several benefits could be
derived for southern pine breeding programs by incorporating ideotypes, conceptual models which
explicitly describe plant phenotypic characteristics that are hypothesized to produce greater yield. The
potential benefits of using ideotypes include improvement in trait heritabilities and genetic correlations, higher genetic gain in diverse silvicultural environments, guidance for developing mating
designs, and provision of a framework for synthesis of tree production physiology knowledge. There
are numerous obstacles to the development of ideotypes for southern pines, most of them related to
the difficulty of linking traits and processes that operate at small spatial and temporal scales (e.g.,
tree crown morphological traits or leaf net photosynthesis) with outputs that occur at large spatial and
temporal scales (e.g., stand-level, rotation-age stem biomass yield). Fortunately, as we enter the 21st
century, several relevant advances are converging that bode well for overcoming these obstacles.
These advances relate to improvements and developments of process modeling, advances in
technologies that permit measures of component processes at relevant scales, the likely future
importance of intensive clonal forestry, and the movement toward large-scale genetic block plot
experiments. FOR. SCI. 47(1):21–28.
