Wood variability in mature longleaf pine: differences related to cardinal direction for a softwood in a humid subtropical climate
Mature longleaf pine (Pinus palustris Mill.) trees were harvested to compare wood property data for opposing bark-to-pith wood strips representing the northern and southern cardinal (or compass) directions. For each of the ten 70-yr-old trees used in the study, wood property data were compared at breast height (BH) and three relative heights: one-quarter height (1Q), midheight (MID), and three-quarter height (3Q). Scanning of the specimens by X-ray densitometry gave specific gravity (SG) profiles that were used to determine wood properties for comparison. No significant differences were determined for wood property data at BH, MID, or 3Q. However, data at 1Q showed higher ring SG (p = 0.043) and percent latewood (p = 0.018) for the northern side, although no differences were observed in the earlywood or latewood SG. This indicated that the higher ring SG for the northern direction results from a greater proportion of latewood. Partitioning the data into estimated juvenile-transition wood and mature wood zones demonstrated that the greater ring SG and percent latewood values in the northern direction occurred within the mature wood zone. Findings presented herein appear to provide the first demonstration of variation in wood properties with respect to cardinal direction for a pine species growing in a humid subtropical climate.