Spatially explicit modelling of biological productivity and economic attractiveness of short rotation woody crops.

Despite of the key role that short rotation woody crops (SRWC) play in supporting bioenergy and the bioeconomy, questions arise about the sustainability of bioenergy. Is it net energy efficient? Is bioenergy carbon neutral? Do SRWC plantations adversely affect food security by competing for land with agriculture? How will SRWC affect biodiversity and provision of environmental services? Answers are elusive and definitive answers require considering specific technology applied at a specific location. Thus, identifying where dedicated SRWC plantations would be viable in terms of biological productivity and economic attractiveness is a necessary first step in order to begin assessing their sustainability. We present a modeling framework using a process-based growth model, 3PG, and geographic information system technology to begin to answer sustainability questions about bioenergy plantations in the southern United States. We assessed potential profitability of four candidate SRWC species, Pinus taeda, Populus deltoides, Eucalyptus grandis, and Eucalyptus benthamii. Estimated yield (mean annual increment) was evaluated as internal rate of return on investment and land expectation value at the 5-digit ZIP code tabulation area level for 13 southern states. The 3PG model incorporates data on weather, soil, and species specific parameters to estimate potential volume production. This approach can be used for as a coarse filter for bioenergy projects that are under construction, in operation, proposed, or where due-diligence is required and to guide more detailed investigations in bioenergy siting-decision support systems. This approach will be most useful for choosing species to plant on former farmland or where landowners may be willing to change species on cutover forestland. The flexibility of the 3PG model allows for different climate scenarios to be developed and to assess risk of failure or lowered yields from extreme events such as drought, as well as altered future climate effects on sustainability. The silvicultural regime used in the model represents current and emerging practice; however, many feasible management regimes and site adaptations have been proposed. For example, the well-developed value chain for loblolly pine in the southern US provide opportunities for diverse silvicultural systems that could incorporate other biomass/bioenergy components, in addition to dedicated SRWC. The yield estimates can be used for further research on sustainability of carbon sequestration. The approach is useful generally as long as sufficient information on species traits is available to model productivity, silvicultural information to estimate management costs, and spatially explicit data on climate, environmental, and growing site conditions exists.