Potential carbon storage in biochar made from logging residue: Basic principles and Southern Oregon case studies

The industrial production of long-lived charcoal products (commonly referred to as biochar) from otherwise shorter-lived logging resides (commonly referred to a slash) has been proposed as a means to increasing terrestrial carbon storage thus mitigating global warming caused by anthropogenic greenhouse gas emissions. We present a generalized model that describes the temporal dynamics of biochar carbon stocks, relative to carbon of unmodified logging residue, and evaluate the sensitivity of carbon storage to various biophysical and production parameters. Using this model, we then attribute net carbon storage to several potential biochar production scenarios, specifically engineered to use wood recovered from harvests prescribed to reduce fire hazard in mixed-conifer forests of South-central Oregon. Relative to a baseline scenario where logging residue is left to decay on site, the net carbon storage attributed to 20 years of biochar production is generally negative for the first several decades, then remains positive for several centuries at levels approximately one-fourth the total feedstock carbon processed. Positive net carbon storage and the time required for it to manifest is notably sensitive to biochar conversion efficiencies, logging residue decay rates, and alternate baseline fates of logging residue. The magnitude of net carbon storage, and the time required for it to become positive, is largely similar across range of production facility types. Moreover, the time required for net carbon storage to become positive, and its magnitude over the first 100 years is notably insensitive to biochar decomposition rates provided biochar decays at least ten-times slower than the logging residue it is made from.

以原本寿命较短的采伐剩余物（logging residues，通常被称为slash）为原料生产长寿命炭制品（生物炭，biochar）的工业化生产方式，已被提议作为提升陆地碳储量、减缓人为温室气体排放引发全球变暖的可行手段。本文提出一款通用模型，用于描述相较于未改性采伐剩余物的生物炭碳库时间动态，并评估碳储量对各类生物物理参数与生产参数的敏感性。基于该模型，我们将净碳储量归因于多种潜在生物炭生产场景，这些场景专门针对利用美国俄勒冈州中南部混交针叶林火灾风险减缓采伐作业中回收的木材进行设计。相较于将采伐剩余物就地腐烂的基准场景，20年生物炭生产带来的净碳储量在最初数十年普遍为负值，随后将在数百年间保持正值，其量级约为加工原料总碳量的四分之一。正净碳储量及其显现所需的时间，对生物炭转化效率、采伐剩余物腐烂速率以及采伐剩余物的替代基准处置方式均具有显著敏感性。净碳储量的大小及其转为正值所需的时间，在各类生产设施类型范围内大体相近。此外，只要生物炭的分解速率至少比其原料采伐剩余物慢10倍，那么净碳储量转为正值所需的时间以及其在前100年的量级，对生物炭分解速率便基本不敏感。