Intensive culture of European black alder in central Indiana, U.S.A.: Biomass yield and potential returns to farmers

Growing interest in woody biomass for energy in the midwestern U.S. will require information on species and site productivities. We investigated 3, 6 and 14 year yields of the nitrogen-fixing tree species. European black alder, at three spacings on a marginally productive soil in central Indiana, U.S.A. The highest yield was 10 Mg ha⁻¹ yr⁻¹ at age three at the closest spacing of 0.5 × 1 m. Other spacings and ages provided smaller yields. Fertilization with phosphorus and potassium only provided a response in the initial 3 year rotation. Whole-tree and stem-only harvests removed varying levels of nutrients from the site. However, on these marginally productive sites where N and sometimes P are limiting, sustainable harvesting could be maintained due to the nitrogen-fixing capability of this species and the effects of N fixation on P availability. Preliminary economic analyses indicated that growing biomass on farms could be profitable, but only with farm or forestry program cost-sharing assistance. Where establishment expenses could be reduced by wider spacings, the use of seed rather than seedlings, or farmer-substituted labor, returns to the farmer were competitive with row-crop and timber production.