GROWTH IN LOBLOLLY-PINE PLANTATIONS AS A FUNCTION OF STAND DENSITY AND CANOPY PROPERTIES

Interrelationships between forest-canopy properties, stand growth, and Reineke's stand density index (SDI) were investigated for unthinned p lots of a loblolly pine, growth-and-yield study, Gross, periodic-annua l increment (I-v) and mean-tree, gross, periodic-annual increment (I-m v) were calculated for the intervals between 17, 22, 27, 32, and 37 ye ars of age. Data to calculate canopy variables were available only aft er age 22, Regression analysis indicates that a second-degree polynomi al of SDI is statistically related to both growth variables during the first two measurement intervals but not the last two, The shape of th e significant equations generally agreed with conventional growth-grow ing stock relationships, and I-v, adjusted for SDI, decreased signific antly with age. Leaf area index (L) and foliage density (F) were linea rly related to SDI for each measurement period. While the equations re lating F and SDI were not significantly different between measurement periods, the intercepts of the fitted equations for L and SDI generall y decreased with plantation age, Mean-live-crown ratio (C-r) was signi ficantly related to SDI for all measurement periods, with the exceptio n of age 32, and canopy depth (C-d) was statistically related to SDI o nly at age 22, Significant multiple-linear regression models were foun d between the growth variables and canopy properties with one exceptio n. With that one exception, I-v was significantly related to L during each measurement interval and to F and C-r during the first two interv als. Mean, gross, periodic-annual increment was statistically related only to those canopy variables that described canopy structure, With t he exception of F, the overall average value of the canopy variables d ecreased with age in these loblolly pine plantations, probably leading to the systematic reduction in I-v with age. Although growth-growing stock relations were not significant in these plantations after age 27 , the relationships between canopy variables and canopy variables emph asize the importance of early density management to maintain vigorous crowns and growth rates as plantations age.