The joint effects of poplar biomass productivity and land costs on poplar production economics were compared for 12 Minnesota counties and two genetic groups, using a process-based model (3-PG) to estimate aboveground biomass productivity. The counties represent three levels of productivity which, due to spatial stratification, were analogous to three biomass supplysheds. An optimal rotation age (ORA) was calculated that minimizes the annualized, discounted per-dry megagrams biomass cost for each county, genetic group and land cover, and for two discount rates (5 and 10 %). The ORA for the lowest-cost county (Todd) with specialist genotypes and a 5 % discount rate is 14 years and the breakeven price at that age is US$71 dry Mg−1, while for the highest-cost county (McLeod), the generalist genotype and a 10 % discount rate, the ORA is 10 years and the breakeven price at that age is US$175 dry Mg−1. Planting after a previous poplar stand increased breakeven prices and increased the ORAs by 1 to 2 years relative to planting after a previous annual crop. An ANOVA analysis showed a significant genetic group effect and significant productivity class × land rent interactions. All other factors being equal, an increase in the discount rate from 5 to 10 % is expected to reduce ORAs by 2 to 3 years. High-productivity supplysheds can also be expected to have ORAs that are 2 to 3 years shorter than low-productivity ones. Land costs were not as closely correlated to productivity as we expected.
Bibliographical noteFunding Information:
This study was funded by the U.S. Forest Service Northern Research Station, Institute for Applied Ecosystem Studies (RWU-NRS-13). We thank Sue Lietz for creating Fig. and our experts for providing information on poplar production practices. We are also grateful to Brad Bender and Gregg Johnson for review of earlier versions of the manuscript.
© 2014, Springer Science+Business Media New York.
- Discount rate
- Land rent