The Effect of Different Forest Management Approaches on the C Stored in the Forest Floor and Soil of Loblolly Pine Plantations.

Extending from Virginia to east Texas in the southeastern United States, managed pine plantations are an important component of the region’s carbon cycle. An objective of the Pine Integrated Network: Education, Mitigation, and Adaptation project (PINEMAP) is to improve estimates of how ecosystem carbon pools respond to the management strategies used to increase the growth of loblolly pine plantations.  Experimental studies (108 total) that had historically been used to understand forest productivity and stand dynamics by university-forest industry cooperatives were measured for the carbon stored in the trees, coarse-wood, forest floor, understory and soils to 1-meter (0-10 cm, 10-20 cm, 20-50 cm, and 50-100 cm).  The age of the studied plantations ranged from 4-26 years at the time of sampling, with 26 years very near the period when these plantations are commonly harvested. The study sites encapsulated a wide regional range in precipitation (1080 mm -1780 mm) and potential evapotranspiration (716 mm – 1200 mm). The most prevalent three soil orders measured were Ultisols (62%), Alfisols (19%), and Spodosols (10%) with Entisols, Inceptisols and 1 Histosol making up the remainder (9%).

Across all study sites, 455 experimental plots were measured. The plots had as a treatment either fertilization, competition control, and stand density control (thinning), including every possible combination of treatments (including ‘no treatment’).  Across all treatment combinations an increase in forest biomass correlated with an increase forest floor C but there was no overall correlation between tree biomass and soil C change. Paired treatment combinations were examined, and for soil and forest floor C pools a consistent treatment effect was where thinning caused a pool of C decrease relative to an unthinned treatment.  These results suggest maintaining higher tree densities would result in greater forest floor and soil C pools in pine plantations.