Effect of harvest residue management on tree productivity and carbon pools during early stand development in a loblolly pine plantation

Abstract

Soil incorporation of postharvest forest floor or logging residues during site preparation increased mineral soil carbon (C) and nitrogen (N) concentration and had a differential effect on early stand growth in a clonal loblolly pine (Pinus taeda L.) plantation. Incorporating 25 Mg ha -1 of forest floor (FF) (C/N ratio ≈ 112:1) or 25 (1LR) or 50 (2LR) Mg ha -1 masticated logging residues (C/N ratio ≈ 856:1) increased soil C concentration by 24-49% in the top 60 cm of soil compared with that for a nontreated control or a raked (R) treatment where the forest floor (-25 Mg ha -1) was removed. Although the long-term treatment effects on soil C are unknown, increased macro-organic matter C (150-2,000 μm) in the recalcitrant heavy fraction coupled with an estimated 20- to 35-year turnover rate for the incorporated residues suggests that soil C will be elevated in the FF, 1LR, and 2LR treatments through the current rotation. There was a treatment × age interaction on stand volume growth (P = 0.03) caused by a differential response to FF and LR treatments. Relative to the control, the FF treatment increased stem volume growth and stand homogeneity, resulting in 18% more stand volume at age 6. In contrast, the LR treatments initially suppressed volume growth; however, at age 6 there were no significant differences in stem volume among control and LR treatments. Six-year stand volume was 116.6, 112.6, 135.1, 116.0, and 112.3 (SE 3.6) m 3 ha -1 in the control, R, FF, 1LR, and 2LR treatments, respectively. Whereas the efficacy of organic matter management will be site-dependent, our results suggest that soil incorporation of forest residues during site preparation can have positive benefits for productivity and building soil C on sites with relatively high inherent soil C stocks. © 2012 by the Society of American Foresters.