Analysis of soybean cropland expansion in the southern Brazilian Amazon and its relation to economic drivers

ABSTRACT The agricultural dynamics of soybean expansion have long been recognized as a major driver of excessive land cover change on the southwestern border of the Brazilian Amazon. The hypothesis that the soybean market exerts an influence on land use was investigated by the association between economic indicators and soybean crop dynamics in the state of Mato Grosso (western Brazil). We integrated a historical series of satellite data of soybean cropland expansion and the two main economic variables (selling prices and production costs) for soybean in Mato Grosso. We focused on the relation between profit (the difference between the average soybean price and production costs) and land-use transition to soybean from 2001 to 2013. The spatially explicit analysis showed that the overall accuracy between the resulting first-time use and the most recent soybean crop area in 2013 was 96.75%, with a Kappa index of 0.63. However, dissimilar values found between Omission and Commission indicators suggest that most of the expanded areas prior to 2013 (5.57 million ha) were under a high dynamical range of land uses. Although there is no direct relation between either the deforestation rate or expansion trends (first-time-use rate) and profit, the results strongly suggest (R2=0.81) that profit exerts a direct and non-negligible influence on the evolution of consolidated land use for soybean in Mato Grosso State.

摘要
长期以来，大豆扩张的农业驱动动态被认为是巴西亚马逊西南边境地区土地覆盖过度变化的主要诱因。本研究以巴西西部马托格罗索州（Mato Grosso）为研究区，通过经济指标与大豆作物动态的关联分析，验证了“大豆市场对土地利用产生影响”这一假说。本研究整合了马托格罗索州大豆农田扩张的历史卫星序列数据，以及该州大豆的两大核心经济变量：销售价格与生产成本。本研究聚焦2001年至2013年间，大豆平均售价与生产成本的差值（即种植利润）和土地利用转为大豆种植的转型之间的关联。空间显式分析（spatially explicit analysis）结果显示，本研究得到的首次开垦地块与2013年最新大豆种植区的总体分类精度为96.75%，Kappa系数（Kappa index）为0.63。不过，漏分误差（Omission）与错分误差（Commission）指标间的数值差异表明，2013年前的大部分扩张地块（557万公顷）处于较高的土地利用动态变化区间内。尽管森林砍伐率、扩张趋势（首次开垦率）与种植利润之间均未体现直接关联，但研究结果（R²=0.81）清晰表明，利润对马托格罗索州大豆种植巩固型土地利用的演化具有直接且不可忽视的影响。