Leaf Area, Stemwood Growth, and Nutrition Relationships in Loblolly Pine

Abstract

Abstract The relationships among loblolly pine (Pinus taeda L.) stand leaf area index (LAD, stemwood volume growth (m3/ha/yr), and growth efficiency (m3stemwood/ha/yr/LAI) were examined in three nitrogen (N) by phosphorus (P) fertilization field trials. Prior to fertilization, stockinglevels and nitrogen limitations varied for the three stands. LAI increased significantly (up to 60%) following N fertilization on the two N deficient stands. Phosphorus additions did not affect LAI. Stemwood growth was positively and linearly related to LAI across treatments and stands. Variationsin LAI across stands reflected the differences in stocking and N availability. On average, a unit of LAI produced 7.3 m3stemwood/ha/yr. Growth efficiency was not affected by fertilization on two of the three stands. A decrease in growth efficiency at a projected LAI above 3.5 resultedfrom an asymptotic relationship between stemwood growth and LAI on a stand that was fully stocked and highly responsive to N fertilization. The use of LAI as an index of stocking is proposed because LAI integrates tree size, stand density, and site resource supply. In addition, it is proposedthat the deviation of a stand's current LAI from the maximum supportable LAI based on fixed site factors (e.g., water, temperature) may provide a good measure of a stand's potential responsiveness to fertilization. For. Sci. 34(3):547-563.