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Forests can partially offset greenhouse gas emissions and contribute to climate change mitigation, mainly through increases in live biomass. We quantified carbon (C) density in 20 managed longleaf pine (Pinus palustris Mill.) forests ranging in age from 5 to 118 years located across the southeastern United States and estimated above- and belowground C trajectories. Ecosystem C stock (all pools including soil C) and aboveground live tree C increased nonlinearly with stand age and the modeled asymptotic maxima were 168 Mg C/ha and 80 Mg C/ha, respectively. Accumulation of ecosystem C with stand age was driven mainly by increases in aboveground live tree C, which ranged from <1 Mg C/ha to 74 Mg C/ha and comprised <1% to 39% of ecosystem C. Live root C (sum of below-stump C, ground penetrating radar measurement of lateral root C, and live fine root C) increased with stand age and represented 4-22% of ecosystem C. Soil C was related to site index, but not to stand age, and made up 39-92% of ecosystem C. Live understory C, forest floor C, downed dead wood C, and standing dead wood C were small fractions of ecosystem C in these frequently burned stands. Stand age and site index accounted for 76% of the variation in ecosystem C among stands. The mean root-to-shoot ratio calculated as the average across all stands (excluding the grass-stage stand) was 0.54 (standard deviation of 0.19) and higher than reports for other conifers. Long-term accumulation of live tree C, combined with the larger role of belowground accumulation of lateral root C than in other forest types, indicates a role of longleaf pine forests in providing disturbance-resistant C storage that can balance the more rapid C accumulation and C removal associated with more intensively managed forests. Although other managed southern pine systems sequester more C over the short-term, we suggest that longleaf pine forests can play a meaningful role in regional forest C management.

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Studies of three-dimensional and two-dimensional condensed phases have shown that manybody interactions contribute ∼ 10% to the equations of state of noble gases. This paper assesses the importance of three-body triple dipole interactions for quasi-one-dimensional phases of He, Ne, H2, Ar, Kr and Xe confined within interstitial channels or on the external surfaces of nanotube bundles. We find the substrate-mediated contribution to be substantial: for interstitial H2 the well depth of the effective pair potential is reduced to approximately one half of its value in free space.We carry out ab initio calculations on linear and equilateral triangular configurations of (H2)3 and find that overlap interactions do not greatly change the DDD interaction in the linear configuration when the lattice spacing is greater than about 3Å. However, the DDD interaction alone is clearly insufficient for the triangular configurations studied.