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Description:
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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 (ε ) 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 . |