Incorporating pruning into the carbon footprint of tree production based on terrestrial laser scanning

Abstract

Pruning is a major source of carbon emissions from urban trees. The high cost of evaluating pruning quantities by destructive measurements has limited the research on pruning. By combining terrestrial laser scanning and quantitative structure models, pruning quantities can be assessed non-destructively. This study focuses on the impact of pruning during tree production, as it is intense and has been rarely evaluated. Using Sophora japonica from a nursery in Beijing as an example, point cloud data were collected from 181 uneven-aged Sophora japonica for the simulation of pruning at a single tree level. All pruning stages were incorporated into the assessment of the carbon footprint of Sophora japonica production for 15-year-old trees. The results show that previous studies have underestimated the tree carbon footprints of pruning, leading to a severe underestimation of the carbon footprint of tree production. Crown reduction removes the most above-ground woody biomass during tree production, over half, while the decomposition of pruning waste is the most significant source of carbon emissions. The removal ratio from pruning of individual trees is consistent within the same pruning pattern. The tree volume can serve as a good predictor for estimating pruning quantities, but crown diameter sometimes needs to be considered. Implementing pruning interventions, harvesting in advance, and choosing appropriate methods for pruning waste disposal can reduce carbon emissions from pruning.