Effects of planting density and genotype on canopy size, canopy structure, and growth of 25-year-old loblolly pine stands in southeastern OklahomaThis article is part of a larger document. View the larger document here.
Leaf biomass and its display within the canopy are important driving variables of stand growth because they reflect a tree or stand’s capacity to intercept radiation, reduce carbon dioxide, and transpire water. We determined the effects of planting density (4- by 4-, 6- by 6-, 8- by 8-, and 10- by 10-foot spacing) on annual needle fall biomass, intercepted radiation, and canopy openness and then related these measures of canopy size to current annual increment and basal area for 25-year-old stands planted with two loblolly pine (Pinus taeda L.) seed sources: North Carolina Coastal (NCC 8-01) and Oklahoma/Arkansas (O/A mix 4213). The study site is located on an excessively drained, mountain site in southeastern Oklahoma. Litter was measured using randomly located traps and summed for a phenological year (Apr. 1 to Mar. 31). Intercepted radiation and canopy openness were measured using hemispherical photographs and the WinScanopy canopy analysis software. After 25 years, initial planting density no longer significantly affected litterfall, intercepted radiation, or canopy openness. Canopy openness was greater for the North Carolina Coastal than the Oklahoma/Arkansas genotypes. Somewhat surprisingly, the measures of canopy size were not related to current annual increments. In contrast, basal area (or standing volume) was correlated to canopy size (R² = 0.12 for litterfall, R² = 0.45 for intercepted radiation, and R2 = 0.13 for canopy openness). Possible reasons for lack of a relationship between canopy size and current annual increment could be due to varying and sometimes intense intraspecific competition, environmental variation across the site, varying and sometimes large amounts of woody biomass relative to foliage, and previous stochastic events. Correlation between basal area and canopy size indicates canopy variables have some ability to predict basal area.