Long-term dynamics of loblolly pine crown structure and aboveground net primary production as affected by site quality, planting density and cultural intensity

Abstract

Crown attributes respond readily to silvicultural manipulations and mediate many aspects of stand structure, consequently they dynamically influence stand production. Numerous studies reported crown structure responses to intensive cultures or stand density and the relation between foliage quantity and growth efficiency at early stages of stand development. Long-term temporal patterns of crown structure and its relation to growth have been much less studied. With long-term remeasurement data from two loblolly pine culture-by-density studies, the roles of planting density, cultural intensity and site quality on crown structure, stand aboveground net primary production (ANPP), and growth efficiency were investigated using ANCOVA and linear mixed-effects modeling approaches. Using data from 480 destructively sampled trees, the Dirichlet regression modeling approach was used to analyze foliage and crown biomass allocations among the lower-, middle- and upper-third crown sections. Stands under different cultural intensities showed different temporal patterns of foliage biomass. Increased planting density or higher site quality enhanced wood production of loblolly pine. ANPP generally increased with increasing site quality, due to increased stand foliage biomass in the early stage of stand development, and mainly due to increased growth efficiency in the late stages of stand development. More intensive cultural treatments increased foliage biomass, thus increased ANPP at early ages; thereafter cultural intensity did not affect foliage biomass, ANPP, and growth efficiency. The trend of early age increases in both foliage biomass and ANPP resulting from increased planting density did not hold true with stand development. After correcting for the effects of tree size and dominance, cultural intensity still altered the vertical distribution of foliage biomass. More intensive culture resulted in an upward shift of foliage biomass.