Growth and wood quality of young loblolly pine trees in relation to stand density and climatic factors

Abstract

A 10-year-old stand of loblolly pine (Pinustaeda L.) in southeastern Oklahoma was thinned to three target basal-area levels: 5.8, 11.5, and 23 m2•ha−1 (control). Specific gravity, latewood percentage, date of transition from earlywood to latewood, growth, and climate variables were measured for 2 years after thinning. Variation in the measured wood properties was more influenced by climatic variation than by the thinning treatments. Diameter growth and per-tree basal-area growth were significantly greater on the thinned treatments both years after thinning. However, stand basal-area growth was greatest on the unthinned treatment. Basal-area growth rates were significantly related to stand basal area, tree size, soil water potential, and air temperature. Early in the summer, growth was positively related to mean daily temperature, while later in the summer, growth was negatively related to mean daily temperature, reflecting the influence of high-temperature stress on growth. A year with high summer rainfall (1984) resulted in wood with a higher percentage of latewood and higher specific gravity than wood produced in a year with low summer rainfall (1985). The date of latewood initiation was significantly related to tree size, soil moisture, and evaporative demand. The date of transition from earlywood to latewood occurred 10–14 days sooner on the unthinned plots in both years. However, annual ring latewood percentage and specific gravity were not significantly affected by thinning. Increased late-season growth rates compensated for the later transition date on the thinned treatments, resulting in no net change in ring latewood percentage due to thinning. The results indicate that individual tree basal-area growth can be increased by thinning without reducing wood density.