Kalt Gerald, Mayer Andreas, Theurl Michaela C, Lauk Christian, Erb Karl-Heinz, Haberl Helmut
Institute of Social Ecology (SEC), Department of Economics and Social Sciences University of Natural Resources & Life Sciences Vienna (BOKU) Austria.
Glob Change Biol Bioenergy. 2019 Nov;11(11):1283-1297. doi: 10.1111/gcbb.12626. Epub 2019 Jun 13.
Short rotation plantations are often considered as holding vast potentials for future global bioenergy supply. In contrast to raising biomass harvests in forests, purpose-grown biomass does not interfere with forest carbon (C) stocks. Provided that agricultural land can be diverted from food and feed production without impairing food security, energy plantations on current agricultural land appear as a beneficial option in terms of renewable, climate-friendly energy supply. However, instead of supporting energy plantations, land could also be devoted to natural succession. It then acts as a long-term C sink which also results in C benefits. We here compare the sink strength of natural succession on arable land with the C saving effects of bioenergy from plantations. Using geographically explicit data on global cropland distribution among climate and ecological zones, regionally specific C accumulation rates are calculated with IPCC default methods and values. C savings from bioenergy are given for a range of displacement factors (DFs), acknowledging the varying efficiency of bioenergy routes and technologies in fossil fuel displacement. A uniform spatial pattern is assumed for succession and bioenergy plantations, and the considered timeframes range from 20 to 100 years. For many parameter settings-in particular, longer timeframes and high DFs-bioenergy yields higher cumulative C savings than natural succession. Still, if woody biomass displaces liquid transport fuels or natural gas-based electricity generation, natural succession is competitive or even superior for timeframes of 20-50 years. This finding has strong implications with climate and environmental policies: Freeing land for natural succession is a worthwhile low-cost natural climate solution that has many co-benefits for biodiversity and other ecosystem services. A considerable risk, however, is C stock losses (i.e., emissions) due to disturbances or land conversion at a later time.
短轮伐期人工林通常被认为在未来全球生物能源供应方面具有巨大潜力。与提高森林生物量收获量不同，专门种植的生物量不会干扰森林碳储量。倘若农业用地能够从粮食和饲料生产中转移出来而不损害粮食安全，那么在当前农业用地上建设能源人工林似乎是可再生、气候友好型能源供应的一个有益选择。然而，土地也可以不用于支持能源人工林，而是用于自然演替。这样它就成为一个长期碳汇，也会带来碳效益。我们在此比较了耕地自然演替的碳汇强度与人工林生物能源的碳节约效果。利用全球农田在气候和生态区域分布的地理明确数据，采用政府间气候变化专门委员会（IPCC）的默认方法和数值计算区域特定的碳积累率。考虑到生物能源路线和技术在替代化石燃料方面效率各异，给出了一系列替代因子（DFs）下生物能源的碳节约量。假设自然演替和生物能源人工林具有统一的空间格局，所考虑的时间范围为20至100年。对于许多参数设置，特别是较长的时间范围和高替代因子，生物能源产生的累计碳节约量高于自然演替。不过，如果木质生物量替代液体运输燃料或天然气发电，在20 - 50年的时间范围内，自然演替具有竞争力甚至更优。这一发现对气候和环境政策具有重要意义：腾出土地用于自然演替是一种值得的低成本自然气候解决方案，对生物多样性和其他生态系统服务有诸多协同效益。然而，一个相当大的风险是后期因干扰或土地转换导致的碳储量损失（即排放）。
