Print PageHybrid poplar plantation is an important biomass crop being evaluated for ethanol production. Predictions of growth and yield under varying growing conditions, soils and climates are critical for farmers and managers planning to establish SRC (short rotation crop) systems.
In this study, we used a workflow management tool, the Predictive Ecophysiological Carbon flux Analyzer (PECAn), to integrate literature data, field measurements and the Ecosystem Demography 2 (ED2) model to estimate yield potential of poplar plantations and the impacts of converting either corn field or forest to poplar plantations on soil carbon (C) sequestration. Model parameters were initially constrained based on ecophysiological traits of poplar compiled from the literature using a hierarchical Bayesian meta-analysis approach. A sensitivity analysis and variance decomposition were conducted to identify the parameters which contribute most to the uncertainties of the ED2 model output. These parameters were further constrained using yield data from a number of different clones and planting densities at one study sites and then the model was verified using yield data from six additional sites. Ensemble model runs were used to propagate uncertainty into the model output by sampling parameters from their posterior distributions. Finally, poplar yields were estimated for the U.S. at a half degree resolution in order to determine potential productivity, estimate the optimal rotation period in different regions, and compare poplar yields to potential perennial grass biofuel yields.
Results/Conclusions
Variance decomposition showed that root respiration, dark respiration, growth respiration, stomatal slope and specific leaf area contributed most to the uncertainty of model results, which suggests that field measurements and further data compilation from literature should focus on these parameters. The ED2 model successfully captured the inter-annual and spatial variability of poplar yield, comparing with field-observed data from multiple sites including independent validation sites. Net soil C sequestration started to increase 15 years after converting corn field or forest to poplar plantations. The regional projection suggests that the maximal annual yield of poplar varied considerably to different soils and climates and could reach 20 tons ha-1 yr-1 in eastern and northern US. The rotation period is suggested to be 6-10 years for the places with high yield potential, though this is likely to be an overestimate as we have not yet included the faster regrowth of coppiced individuals. In conclusion, poplar plantation is predicted to have high yield potential across wide range of climates and soils and be sustainable in soil C sequestration.
