Functional Approach to Simulating Short-Rotation Woody Crops in Process-Based Models

Short-rotation woody crops (SRWCs) such as Populus have great potential as biofuel feedstocks. Biomass yields and yield stability at potential sites are important considerations when SRWCs are widely planted. The process-based, daily time-step simulation model Agricultural Land Management Alternative with Numerical Assessment Criteria (ALMANAC) offers promise as a useful tool to evaluate tree growth over large ranges of conditions. The objective of this study was to develop algorithms and growth parameters of hybrid poplar 'Tristis #1' (Populus balsamifera L. x Populus tristis Fisch) and eastern cottonwood (Populus deltoides Bartr.) in ALMANAC and to improve simulation of leaf area index (LAI) and plant biomass as well as biomass partitioning. ALMANAC with the improved algorithms for LAI and weight of falling leaves was applied to hybrid poplar plots in Wisconsin and cottonwood plots in Mississippi, and the modeled biomass yield and LAI were compared with measured data to modify and evaluate the location-specific ALMANAC models. Improved algorithms for LAI and biomass simulation and suggested values and potential parameter ranges for hybrid poplar and cottonwood were reasonable (Nash-Sutcliffe model efficiency (NSE) 0.81 +/- 0.99 and R (2) 0.76 +/- 0.99). ALMANAC with modified algorithms and parameters for Populus growth realistically simulated LAI, aboveground woody biomass, and root biomass of Populus. Thus, this model can be used for biofeedstock production modeling for Populus. The improved algorithms of LAI and biomass simulation for tree growth should also be useful for other process-based models, such as Soil and Water Assessment Tool (SWAT), Environmental Policy Integrated Climate (EPIC), and Agricultural Policy/Environmental eXtender (APEX).