Linking morphology and physiology as predictors of productivity in elite families of southern pines
Crown architecture affects tree growth through the control of leaf area and its display. Yet the linkages between crown structure, leaf traits, and productivity of elite selections of forest trees and responses to intensive silviculture are not fully understood. It was hypothesized that trees with crown and leaf traits governing efficient light capture and photosynthesis at the canopy scale would be the most productive. To this end, families of loblolly (Pinus taeda) and slash pine (Pinus elliottii) were grown at three experimental sites in the West Gulf Coastal Plain of Texas and Louisiana under two silvicultural treatments, including repeated fertilization with control of competing vegetation (HI), and a control (C) consisting of fertilization at planting. Families and species differed in crown traits and aboveground productivity, and genotype differences increased throughout the first 5 years of stand development. Crown shape was important for light interception and growth initially, but at the onset of canopy closure, crown size, stand leaf area and its distribution within crowns affected canopy light interception and tree growth. Among all families and treatments, aboveground biomass productivity was positively related to absorbed photosynthetically active radiation (APAR) and canopy photosynthesis. Light-use efficiency (?) varied from 0.41 to 0.56 g MJ-1 among families and was lowest in slash pine. Variability in aboveground biomass growth was related more to stand leaf area and APAR than to differences in light-use efficiency in these young stands. Leaf physiological, chemical and morphological attributes changed within crowns in accordance with developing light availability gradients. Physiological attributes, such as net photosynthesis, were better predictors of family performance when integrated at the canopy level than leaf level in the examined pine species. Crown size, light absorption, and aboveground growth generally ranked higher in the HI treatment than in the control, although the effects of the intensive silvicultural treatments did not differ statistically. Family performance was independent of treatment. Crown and canopy attributes, such as high leaf area index and large crowns with low leaf area density per crown volume, may be useful in the selection of highly productive genotypes of loblolly and slash pine under intensive silviculture.