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, CO2 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 (CO2) 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 CO2 by age 60 years in the Brown soil zone, compared to 2086 t CO2 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 CO2, respectively over the same period. If a landowner decides to remove a 60-year-old shelterbelt, 1205 t CO2 is lost within a short period after removal, whereas 718 t of remaining CO2 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.

中文翻译：

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加拿大萨斯喀彻温省防护林的碳生命周期评估。

防护林是在农场和田地周围种植的一排排树木，用于防止水土流失、促进生物多样性和野生动物栖息地。此外，通过树木生物量的增长和农业土壤中的碳汇来固碳。近年来，拆除防护林变得越来越普遍，因为在作物价格上涨的情况下首选农田，导致温室气体排放增加和碳汇减少。土地所有者很可能在不了解这些树木固存的碳的情况下做出决定。在这项研究中，使用碳生命周期分析方法估计了在萨斯喀彻温省发现的六种常见防护林树种（杂交杨树、绿灰树、马尼托巴枫树、苏格兰松树、白云杉和锦鸡儿）的碳固存水平。对五个封存/排放阶段估算的碳封存净量 - 1) 幼苗生产，2) 幼苗到农场的运输，3) 种植，4) 维护，以及 5) 农场防护林的生长。由于一些土地所有者正在拆除防护林带，因此还包括拆除阶段。在拆除防护林带期间，CO2 排放是通过以下方式产生的：(i) 拆除树木和随后燃烧木材的物理过程；(ii) 长期清除后土壤碳的损失。分析的功能单位是一公里的防护林，是农用防护林的正常结构。通过将二氧化碳的分子量乘以碳的分子量 (44/12)，将所有排放/封存水平作为二氧化碳 (CO2) 进行测量。除了防护林的生长阶段，所有其他阶段都贡献了净温室气体排放，这被树木生长过程中的碳固存抵消了。杂交杨树是一种快速生长的树种，在所有土壤区的六种树种中固碳最多。一公里长的混合杨树防护林在布朗土壤区在 60 年之前隔离了 1923 吨二氧化碳，而黑土区同期则为 2086 吨二氧化碳。相比之下，在布朗土壤区，马尼托巴枫树和白云杉同期分别固存了 756 吨和 732 吨二氧化碳。如果土地所有者决定拆除已有 60 年历史的防护林，则拆除后的短时间内会损失 1205 吨二氧化碳，而剩余的 718 吨二氧化碳作为死有机物保留，并在一段时间内缓慢释放。