Aboveground biomass partitioning in loblolly pine silvopastoral stands: Spatial configuration and pruning effects

Patterns of biomass partitioning have been extensively studied in loblolly pine (Pinus taeda L.) plantations and natural stands, but not in silvopastoral practices, which are being promoted in southern United States. We conducted aboveground biomass harvests in 18-year-old loblolly pine growing in single-, double-, and quadruple-row configurations at 2.1 m between trees in the row, and initial densities of 308, 568, and 932 trees ha−1. In the double- and quadruple-row configurations, rows were 2.4 m apart while alleys were 14.6 m wide in all configurations. Trees were felled from single, double (east and west orientations) and, the exterior east and one of the interior (trees identified as QR2) quadruple rows, and separated into bole, branches, twigs (<2 cm in diameter), and foliage. In total, 60 trees within the 25-29 cm DBH class were sampled (five configurations × three trees per row × two pruning regimes × two replicates). Averaged across pruning regimes, absolute total aboveground biomass per tree ranged from 366 kg in single-row trees to 231 kg in QR2-trees while bole biomass varied from 185 kg in single-row trees to 143 kg in QR2-trees. Configuration affected relative biomass partitioning to boles (P < 0.05), which ranged, on an average, from 60% of total tree biomass in quadruple rows to 52% in single rows, branch (P < 0.05), which varied from 30% in single rows to 24% in quadruple rows, and foliage (P < 0.001), which ranged from 12% in single rows to 8% in quadruple rows. Bole DBH and available ground space per tree (as covariates) did not affect biomass partitioning as neither did pruning, although pruning markedly improved log quality. Basal areas in single-, double-, and quadruple-row configurations in the silvopasture were 11, 19, and 34% greater than the projected basal areas for adjacent loblolly pine plots with similar stand density.