Soil Carbon and CO2 Efflux as Influenced by the Thinning of Loblolly Pine (Pinus taeda L.) Plantations on the Piedmont of Virginia

Abstract

Abstract The thinning of loblolly pine plantations has a great potential to influence the fluxes and storage of carbon within managed stands. In this study we investigated the effects of thinning on mineral soil carbon distribution and storage 14 years after the thinning of an 8-year-old loblolly pine plantation on the Piedmont of Virginia. Additionally, we examined patterns of soil CO2 efflux (Es) for 1 year after the second thinning of the same stands at age 22. The study was conducted using three replicate 0.22-ha stands planted using 3.05 × 3.05 m spacing in 1980. Soil carbon in the fine soil fraction (<2 mm) was evenly dispersed throughout thinned plots, and random sampling techniques were adequate for capturing spatial variability. Soil carbon decreased with depth, was higher at all depths in thinned stands, and was significantly higher (P = 0.06) at the 10- to 20-cm depth in the thinned stands (1.04%) compared with unthinned stands (0.76%). Soil temperature was approximately 1–2°C warmer in the growing season and 1°C cooler in the dormant season in thinned stands. Soil moisture was consistently higher in thinned stands by approximately 5%. Temperature was positively and significantly correlated with Es in thinned and unthinned stands. When modeled using regression, thinning was a significant variable for predicting Es (P < 0.0009) but explained less than 1% of the variation. Whereas thinning decreased Es when standardized to a constant temperature, actual Es was elevated in thinned stands because of higher soil temperature.