SEASONAL CAMBIAL GROWTH AND DEVELOPMENT OF LOBLOLLY-PINE - XYLEM FORMATION, INNER BARK CHEMISTRY, RESIN DUCTS, AND RESIN FLOW

Cambial activity of loblolly pine in central Louisiana under mild soilwater deficit lasted for 252 days, one-third of which was used in the formation of early-wood. Although more cells formed in the late-wood, the radial increments for both were statistically similar ( 1750-mu-m). Vertical resin duct formation started 12 weeks after cambial reactivation with the first duct in each tree, except two, forming at the early-wood. Resin flow, an important factor in pine resistance to bark beetle attack, was moderately correlated with vertical duct density, growth variables, and all measured environmental variables with total soilwater storage, cumulative water deficit, and maximum air temperature combined accounting for 73% of the variation. Levels of starch continuously declined from May to December, while total sugar fluctuated with no seasonal pattern. Amino nitrogen and total nitrogen changed seasonally with peak concentrations coinciding with cell initiation and active growth, leaf fall, and winter cold temperatures. Seasonal change in resin flow was associated with changes in physiology related to ontogeny as well as environment. Knowledge of such relationships improves the basis for future study of pine/bark beetle interactions.