Nondestructive Estimation of Biomass Yield for Short-Rotation Woody Crops Is Reliable and Shows High Yields for Commercial Stands in Bavaria

Abstract

Realistic yield data are essential for evaluating the economic viability of short-rotation woody crops (SRWC). However, we lack not only realistic yield data, particularly for commercial stands, but also easily applicable methods to estimate biomass. To address these shortcomings, we evaluated 30 commercial stands in Bavaria during the first rotation (not yet coppiced) using three different methods—the quadratic mean diameter (QMD) approach, the yield appraiser (YA), and allometric power equations (APE). Of the three, APE requires the highest sampling effort, data, and expertise. APE was used to establish a baseline for bias and precision to assess the performance of the QMD and YA methods. We found that neither the QMD nor the YA produced biomass estimation results different to that of the APE. Commercial stands 5 years old or older yielded, on average, 8.9 odt ha−1 a−1, more than field trials of comparable age in the first rotation in Bavaria. This finding contradicts the common expectation that field trials yield more biomass than commercial stands. The mean annual increment in 3-year-old stands was significantly lower than that in stands 5 years old or older with comparable planting densities. Given that measured yields varied widely around the mean, economic evaluations should not use means, but take into account uncertainties. We found that YA and QMD are generally suitable biomass estimation methods for practitioners, with the QMD approach providing higher accuracy due to a lower relative bias and relative precision (−6.15 and 13.3 %) than YA (−12.97 and 21.87 %).