| To evaluate the environmental benefits that might accrue from the conversion of farmland to short-rotation woody crops (SRWC), a hypothetical conversion of corn, soybean and wheat fields to hybrid poplar was modeled in the High Island Creek subwatershed of the Lower Minnesota River.; The ADAPT hydrologic model was used to simulate the water quality impacts of 10, 20, and 30% cropland conversion to SRWCs grown on a five-year rotation. Conversion to SRWC reduced cumulative annual flows by up to 9 percent, sediment by up to 28 percent, and nitrogen loading by up to 15 percent, although mean annual phosphorus loadings were up to 7 percent higher.; The value of sediment reductions was with respect to road ditch and culvert maintenance costs were obtained through a survey of township and county road authorities, while drainage ditch maintenance costs were obtained from counties and from the watershed district. Potential annual public savings amounted to {dollar}9.37 per Mg of sediment not delivered to the watershed outlet.; A boating-use model and the Unit Day Value method were combined to estimate the recreational value of sediment reduction to users of area lakes. At over 20% cropland conversion, improved recreational conditions resulted in increases in annual recreational value of {dollar}1.92–2.90 per hectare of converted cropland.; Based on literature values for carbon emissions, hybrid poplars over a rotation produced an estimated annual economic value, due to carbon sequestration of {dollar}13–15 per hectare when used for bioenergy and {dollar}29–33 per hectare when converted to wood products. If these hybrid poplars were substituted for aspen traditionally harvested from natural woodlands, the poplars create an annual forest preservation value of {dollar}4.79–5.44 per hectare depending on the percentage of cropland converted to poplars.; To account for the uncertainty inherent in non-market benefit estimation, a Monte Carlo simulation approach was used to produce an estimated range and distribution of environmental benefit values for cropland conversion to SRWC. Because (at present) these values are not accounted for in the market price for this crop, the average net benefits justify annual public subsidies ranging from {dollar}48 to {dollar}99 per hectare. |
