Effects of Planting Density and Seed Source on Loblolly Pine Stands in Southeastern Oklahoma
Since the early 1970s, loblolly pine (Pinus taeda L.) plantations have been established west of the native range of the species in the Ouachita Mountains of Oklahoma, using faster-growing seed sources from coastal North Carolina (NCC) rather than Oklahoma or Arkansas (O/A). Although the NCC sources outperform O/A sources early in stand development, it is not known how these provenances will perform later in stand development when density-dependent mortality is occurring. We tested the effects of planting density (1,075, 1,680, 2,990, and 6,725 trees ha−1) and seed source (NCC and O/A) on stand and tree attributes for 25-year-old plantations located on a droughty, mountain soil in southeastern Oklahoma. Survival decreased with increasing stand density but did not differ among sources. Average tree diameter also decreased with increasing planting density (25.5 to 15.8 cm), and, again, the pattern was consistent across provenances. Average tree heights decreased with stand density (18.6 to 16.8 m); however, the NCC seed source was taller than the O/A seed source (18.4 versus 17.0 m). This resulted in NCC stands maintaining greater stand volume than O/A stands (329 versus 301 m3 ha−1). Basal area was similar among seed sources and did not significantly differ among densities (average 49.0 m2 ha−1). These results indicate that over 25 years, the NCC seed source performed better than the regional seed source even when grown under extremely high densities and experiencing density-dependent mortality.