Aboveground biomass equations for black willow (Salix nigra Marsh.) and eastern cottonwood (Populus deltoides Bartr. ex Marsh.)

Abstract

Black willow and eastern cottonwood are fast-growing hardwoods native to river bottoms throughout the southeastern United States, e.g., the Lower Mississippi Alluvial Valley (LMAV), that are often grown as short rotation woody crops (SRWCs) because of their potential to provide high biomass yields in short periods of time. This study focused on developing allometric equations to estimate individual tree, coppice, and stand level aboveground biomass (AGB) of these species using data from destructively sampled trees collected through the age of 6 years. Diameter at breast height (dbh), total stem height, and their transformations and combinations were the predictors of individual tree AGB. Coppice models included number of stems in the coppice as an additional predictor variable. The stand level AGB was predicted using planting density, dominant height, and stand age. A logarithmic model that used dbh squared then multiplied by total stem height was the best fitting model (Adj. R2 = 0.982, RMSE = 1.13 kg) for the individual tree AGB estimation for black willow. Whereas a model that used dbh and total stem height as separate predictors was the best fitting model (Adj. R2 = 0.954, RMSE = 2.90 kg) for eastern cottonwood. Using the number of stems as an additional predictor in the coppice models reduced RMSE by 5.67% for black willow and by 4.95% for eastern cottonwood. The stand level models explained 79.5% and 94.1% of the variation in stand AGB for black willow and eastern cottonwood and had RMSEs of 2.38 and 6.59 Mg/ha, respectively. Overall, these models will be useful for forestland owners in the LMAV for estimating available bioenergy feedstock from black willow and eastern cottonwood plantations without requiring destructive sampling.

Keywords

• Short rotation woody crops (SRWCs)
• Biomass estimation
• Lower Mississippi alluvial valley (LMAV)
• Bioenergy