Environmental benefits of cropland conversion to hybrid poplar: Economic and policy considerations

To evaluate environmental benefits that might accrue from conversion of farmland to short-rotation woody crops (SRWC), a hypothetical conversion of 10%, 20% and 30% of cropland was modeled in a watershed of the Lower Minnesota River. The analysis synthesized output from a watershed model (ADAPT) with literature-based estimates of productivity and economic values for water quality, forest conservation and carbon sequestration. A Monte Carlo simulation approach was used to estimate ranges of environmental benefit values for cropland conversion to SRWCs. The summed average net benefits justified annual public subsidies ranging from $44 to $96ha ^-1, depending on market scenario and conversion level. Cropland conversion to SRWCs reduced cumulative annual stream flows, sediment and nitrogen loadings by up to 9%, 28% and 15%, respectively. Reduced sediment loads resulted in potential average annual public savings on culvert and ditch maintenance costs of $9.37Mg ^-1 of sediment not delivered to the watershed outlet. Hybrid poplars over a 5-year rotation produced an estimated annual economic value due to carbon sequestration of $13-15ha ^-1 when used for bioenergy and $29-33ha ^-1 (depending on conversion rate) when converted to wood products. If hybrid poplars are substituted for aspen traditionally harvested from natural woodlands, the poplars create annual forest preservation values of $4.79-5.44ha ^-1.