Published in Proceedings of the Ninth Biennial Southern Silvilcultural Research Conference, January 1, 1998, pages 564-568. This article is in the public domain. Published by the Pacific Southwest Research Station, USDA Forest Service.
NOTE: At the time of publication, the author Christopher Dicus was not yet affiliated with Cal Poly.
Growth and yield data from a loblolly pine plantation in southeastern Louisiana were obtained yearly from 1993 to 1996 on numbered trees within two stands initially planted on a 1.22- by 1.22-meter spacing, and two stands planted on a 2.44- by 2.44-meter spacing. Using allometric equations derived from a 1994 on-site destructive harvest, cited nitrogen concentrations of various tree tissues, and accounting for foliar nitrogen retranslocation, stand growth and soil nitrogen demands were determined.
Results showed that production of all aboveground tissues increased as stand density index (SDI) increased. Annual soil nitrogen demand increased with SDI primarily as a result of an increase in nitrogen-rich foliage on the denser sites. Below ground production, as estimated from minirhizotron censuses, also increased as SDI and aboveground nitrogen demands increased. More fine-root production per unit aboveground nitrogen demand was observed on less fertile plots. Stemwood production per unit leaf biomass decreased with increasing SDI, and is assumed to be the result of a greater percentage of total net primary production being partitioned to fine-root production in the denser plots.
The results of this study suggest that the density of forest stands may influence nutrient demands from the soil and subsequent belowground productivity through differential aboveground biomass allocation patterns and tissue nitrogen concentrations.