SOIL CARBON SEQUESTRATION BENEATH HYBRID POPLAR PLANTATIONS IN THE NORTH CENTRAL UNITED-STATES

Hybrid poplar plantations grown on tilled agricultural lands previously in prairie, sequester significant quantities of soil carbon. Comparisons are made between hybrid poplar plantations and adjacent row crops or mowed grass. Establishing and tending plantations often results in early soil carbon loss, but soil carbon is significantly related (positive) to tree age. Increasing tree age eventually results in a net addition of soil carbon from plantations older than about 6 to 12 years of age. Soil carbon loss under trees occurred most frequently from the surface 30 cm early in the plantation history-evidence that the loss was due to mineralization. Soil carbon gain was most significant in the 30 50 cm layer and was attributed to tree root growth. Soil carbon accretion rate beneath 12- to 18-year-old poplar plantations exceeded that of adjacent agricultural crops by 1.63 +/- 0.16 Mg ha-1 yr-1. There was a significant crop x soil depth interaction for bulk density with bulk density lower beneath trees in the 0 30 cm layer and higher in the 30-50 cm layer. There was little evidence of carbon trapping of wind-blown organic detritus by tree plantations in the prairie environment