Rudd Lindsey, Kulshreshtha Suren, Belcher Ken, Amichev Beyhan
School of Environment and Sustainability, University of Saskatchewan, Saskatoon, SK, S7N 5A8, Canada.
Department of Agricultural and Resource Economics, University of Saskatchewan, Saskatoon, SK, S7N 5A8, Canada.
J Environ Manage. 2021 Nov 1;297:113400. doi: 10.1016/j.jenvman.2021.113400. Epub 2021 Jul 31.
Shelterbelts are rows of trees planted around farmyards and field for protection against soil erosion, promotion of biodiversity and wildlife habitat. Additionally, to carbon sequestration through growth in tree biomass and carbon sinks in agricultural soil. In recent years, removal of shelterbelts has become more common, as crop land is preferred under higher crop prices, resulting in increased GHG emissions and decreases in carbon sinks. It is likely that landowners are making decisions without the knowledge of carbon sequestered by these trees. In this study, the level of carbon sequestration for the six common shelterbelt tree species found in Saskatchewan (hybrid poplar, green ash, Manitoba maple, Scots pine, white spruce, and caragana) was estimated using a carbon - life cycle analysis method. Net amount of carbon sequestered was estimated for five sequestration/emission stages - 1) seedling production, 2) transportation of seedlings to farm, 3) planting, 4) maintenance, and 5) growth of shelterbelts on farm. Since some landowners are removing shelterbelts, a removal stage was also included. During removal of shelterbelts, CO emissions were produced through: (i) physical process of removing the trees and subsequent burning of the wood; and (ii) loss of soil carbon after the removal over a long period of time. The functional unit for the analysis was one linear kilometer of shelterbelt, the normal structure of shelterbelts on agricultural land. All emissions/sequestration levels were measured as carbon dioxide (CO) by multiplying the molecular weight of carbon dioxide to that of carbon (44/12). Other than the growth stage of shelterbelts, all other stages contributed net greenhouse gas emissions, which offset by carbon sequestration during tree growth. Hybrid poplar is a rapidly growing tree and sequesters the most carbon of the six species in all soil zones. A one km long hybrid poplar shelterbelt sequestered upwards of 1923 t CO by age 60 years in the Brown soil zone, compared to 2086 t CO over the same period in the Black soil zone. In comparison, in the Brown soil zone, Manitoba maple and white spruce sequestered 756 and 732 t CO, respectively over the same period. If a landowner decides to remove a 60-year-old shelterbelt, 1205 t CO is lost within a short period after removal, whereas 718 t of remaining CO is retained as dead organic matter, which is slowly released over a period. Although field shelterbelts may emit greenhouse gases in the earlier stages of development, overall, they are net sinks of carbon and can therefore play a significant role in Canada's plan to reduce GHG emissions from agriculture.
防护林带是环绕农家院和农田种植的一排排树木，用于防止土壤侵蚀、促进生物多样性和提供野生动物栖息地。此外，通过树木生物量的增长和农业土壤中的碳汇来实现碳固存。近年来，随着作物价格上涨，耕地更受青睐，防护林带的移除变得更加普遍，这导致温室气体排放量增加和碳汇减少。土地所有者在做决策时可能并不了解这些树木的碳固存情况。在本研究中，使用碳生命周期分析方法估算了萨斯喀彻温省发现的六种常见防护林带树种（杂交杨树、绿梣、曼尼托巴枫、苏格兰松、白云杉和锦鸡儿）的碳固存水平。估算了五个固存/排放阶段的碳固存净量——1）苗木生产，2）将苗木运输到农场，3）种植，4）养护，5）农场防护林带的生长。由于一些土地所有者正在移除防护林带，因此还包括了移除阶段。在移除防护林带期间，通过以下方式产生二氧化碳排放：（i）砍伐树木及随后焚烧木材的物理过程；（ii）移除后长时间内土壤碳的流失。分析的功能单位是一公里长的防护林带，这是农田防护林带的正常结构。所有排放/固存水平均以二氧化碳（CO₂）衡量，通过将二氧化碳的分子量乘以碳的分子量（44/12）来计算。除了防护林带的生长阶段外，所有其他阶段都产生净温室气体排放，这些排放被树木生长期间的碳固存所抵消。杂交杨树是一种生长迅速的树种，在所有土壤区域中，它在六种树种中固存的碳最多。在棕色土壤区，一条一公里长的杂交杨防护林带到60岁时固存的二氧化碳超过1923吨，而在黑色土壤区同期固存2086吨二氧化碳。相比之下，在棕色土壤区，曼尼托巴枫和白云杉在同一时期分别固存756吨和732吨二氧化碳。如果土地所有者决定移除一条60年树龄的防护林带，移除后短期内会损失1205吨二氧化碳，而剩余的718吨二氧化碳以死有机物质的形式保留，会在一段时间内缓慢释放。虽然农田防护林带在早期发展阶段可能会排放温室气体，但总体而言，它们是碳的净汇，因此在加拿大减少农业温室气体排放的计划中可以发挥重要作用。
