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Dynamics of savanna clearing and land degradation in the newest agricultural frontier in Brazil
GIScience & Remote Sensing ( IF 6.7 ) Pub Date : 2020-10-02 , DOI: 10.1080/15481603.2020.1835080
Alana Almeida de Souza 1 , Lênio Soares Galvão 1 , Thales Sehn Korting 1 , Juan Doblas Prieto 1
Affiliation  

ABSTRACT We investigated the dynamics of savanna clearing and land degradation in the MATOPIBA region, the newest agricultural frontier over the Cerrado in Brazil. For geospatial analysis of the “big data,” we used algorithms available on the Google Earth Engine (GEE) platform along with different satellite products. For the detection of vegetation clearing in the 1985–2018 period, we applied the LandTrendr algorithm to the normalized difference vegetation index (NDVI) obtained from Landsat satellite instruments. In the evaluation of land degradation (2001–2015), we used the Trends.Earth algorithm to analyze NDVI data calculated from the Moderate Resolution Imaging Spectroradiometer (MODIS). By combining different datasets into the analysis, we discussed the relationships among savanna clearings, land degradation, topographic attributes, and fire frequency. The results showed that the largest proportions of savanna clearing in the 1985–1990 period were detected in the south of MATOPIBA (mesoregions Ocidental do Tocantins and Extremo Oeste Baiano). The savanna clearing progressed toward the mesoregions Oriental do Tocantins, Sudoeste Piauiense, and Sul Maranhense between 1991 and 2005. Variations over time in cleared areas ranged from 0.086 Mha to 2.146 Mha per year, showing well-defined peaks in 1986, 1991, and 2012. The clearing events followed the soybean expansion, especially over flat terrains at high elevations. In addition to the spillover effects of the Amazon Soy Moratorium on the savannas, other political and economic factors promoted changes in cleared areas of MATOPIBA. Compared to the decade preceding the signature of the Amazon Soy Moratorium in 2006, the cleared area of MATOPIBA increased 41% in the 10-year post-moratorium period. In the other analysis, our Trends.Earth results showed that the largest proportions of land degradation areas, as proxied by the MODIS NDVI, were the Sudoeste Piauiense and Centro Maranhense. These mesoregions presented distinct patterns of precipitation and soil composition. The number of fire events increased with vegetation clearing. However, the amount of cleared areas correlated moderately with that of burned areas due to the multi-use of fire in the region. Finally, we observed that the amount of land-degraded areas increased with fire frequency over agricultural areas, but remained relatively stable over native vegetated areas. Results highlight the importance of satellite sensors and cloud-computing platforms to inspect long-term trajectories of land occupation and degradation over broad savanna areas.

中文翻译:

巴西最新农业前沿的稀树草原清理和土地退化动态

摘要 我们调查了马托皮巴地区热带稀树草原清理和土地退化的动态,马托皮巴地区是巴西塞拉多最新的农业前沿。对于“大数据”的地理空间分析,我们使用了 Google Earth Engine (GEE) 平台上可用的算法以及不同的卫星产品。对于1985-2018年期间植被清除的检测,我们将LandTrendr算法应用于Landsat卫星仪器获得的归一化差异植被指数(NDVI)。在土地退化评估(2001-2015)中,我们使用 Trends.Earth 算法来分析由中分辨率成像光谱仪 (MODIS) 计算出的 NDVI 数据。通过将不同的数据集结合到分析中,我们讨论了稀树草原空地、土地退化、地形属性、和火灾频率。结果表明,在 1985 年至 1990 年期间,在 MATOPIBA 南部(中间区域 Ocidental do Tocantins 和 Extremo Oeste Baiano)发现了最大比例的稀树草原清理。1991 年至 2005 年间,热带稀树草原向中区域东方 do Tocantins、Sudoeste Piauiense 和 Sul Maranhense 进行了清理。清理区域随时间的变化范围为每年 0.086 Mha 至 2.146 Mha,在 1986 年和 1986 年出现明确的峰值. 清空事件发生在大豆扩张之后,尤其是在高海拔的平坦地形上。除了亚马逊大豆禁令对热带草原的溢出效应外,其他政治和经济因素也促进了马托皮巴清理区的变化。与 2006 年签署亚马逊大豆禁令之前的十年相比,在 10 年的暂停期后,马托皮巴的清理面积增加了 41%。在另一项分析中,我们的 Trends.Earth 结果显示,以 MODIS NDVI 为代表的最大比例的土地退化区域是 Sudoeste Pauuiense 和 Centro Maranhense。这些中区呈现出不同的降水和土壤成分模式。火灾事件的数量随着植被清除而增加。然而,由于该地区多次使用火灾,清除区域的数量与燃烧区域的数量适度相关。最后,我们观察到土地退化面积在农业区随着火灾频率的增加而增加,但在原生植被区保持相对稳定。
更新日期:2020-10-02
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