Development of a method for estimating stand volume in broad-leaved forest stands—Towards assessing the forest removals needed to achieve net zero emissions—

Abstract

This study aimed to examine methods for estimating stand volume of broad-leaved forests. Accurate estimation of aboveground biomass is essential for calculating forest carbon sinks and achieving Japan’s carbon neutrality goals. Due to discrepancies between forest registration and current forest conditions, time-series data from the National Forest Inventory (NFI) during the third and fourth periods were used to predict the future volume of broad-leaved forest stands. The country was divided into six regions. For each region, the relationship between the stand age and average upper tree height was modeled using the Korf equation and the generalized algebraic difference approach. Stand volume was then estimated by fitting a smoothing spline to the relationship between the average upper tree height and the stand volume. The tree height growth patterns varied by region; lower latitude regions tended to have smaller upper tree height growth limits. In several regions, the estimated stand volume was larger than the values obtained in previous studies using stand yield tables. However, the estimated values tended to asymptotically approach a constant value. Using this method, future stand volumes can be estimated and predicted using the average stand information for each region. More detailed predictions at the stand plot level can be obtained in the future by combining this method with forest age data from the forest register and height information from airborne LiDAR measurements. Growth functions should be optimized for each region, and the latest NFI data should be used to improve model accuracy.