Impacts of reforestation on soil and soil organic carbon losses

ABSTRACT Water erosion is a serious environmental problem that causes soil degradation, compromises its fertility and causes soil organic carbon (SOC) losses. Reforestation, encouraged by Brazilian environmental legislation, is a way to reduce water erosion. However, in tropical and subtropical regions, there is little information on the impact of reforestation on soil loss rates and SOC. Therefore, this study aimed to apply the Erosion Potential Method, combined with multitemporal data from soil samples collected in situ, to estimate and spatialize soil and SOC losses in a predominantly agricultural Brazilian watershed that showed high rates of reforestation in the period studied from 2011 to 2019. The determination of the EPM parameters was carried out with the aid of a Geographic Information System and the soil loss estimate was validated with information from a hydrosedimentological collection station. The results showed that between 2011 and 2019 water erosion was reduced by 27.5%, while carbon losses were reduced by 32.7%. Among the evaluated crops, corn showed the highest soil and SOC losses, while coffee and forest areas exhibited the lowest rates. Reforestation of the basin is the main factor responsible for the reduction of soil losses. This process was initiated seeking to meet the requirements of the Brazilian Forest Code, which highlights the positive role that public policies can play in environmental conservation when respected and well applied.

摘要：水蚀是一类严重的环境问题，会引发土壤退化、降低土壤肥力，并造成土壤有机碳（soil organic carbon，SOC）流失。巴西环境立法所鼓励的再造林，是减轻水蚀的有效手段。但在热带、亚热带地区，有关再造林对土壤流失速率及土壤有机碳影响的公开研究数据仍较为匮乏。为此，本研究结合原位采集的多时序土壤样本数据，应用侵蚀潜力法（Erosion Potential Method，EPM），对2011至2019年研究期内再造林率较高的巴西农业主导型流域的土壤及土壤有机碳流失量进行估算与空间可视化分析。本研究借助地理信息系统（Geographic Information System，GIS）确定侵蚀潜力法的相关参数，并通过水文泥沙监测站的实测数据对土壤流失量的估算结果进行验证。研究结果表明，2011至2019年间，流域水蚀强度降低了27.5%，有机碳流失量减少了32.7%。在参评的作物类型中，玉米的土壤及土壤有机碳流失量最高，而咖啡种植区与林地的流失率最低。流域再造林是土壤流失量降低的核心驱动因素。本次再造林活动最初旨在满足《巴西森林法》的相关要求，该案例凸显了公共政策在得到尊重与妥善落实后，可对环境保护发挥积极作用。