Agricultural expansion into subtropical and tropical forests causes major environmental damage, but its wider social impacts often remain hidden. Forest-dependent smallholders are particularly strongly impacted, as they crucially rely on forest resources, are typically poor, and often lack institutional support. Our goal was to assess forest-smallholder dynamics in relation to expanding commodity agriculture. Using high-resolution satellite images across the entire South American Gran Chaco, a global deforestation hotspot, we digitize individual forest-smallholder homesteads (n = 23,954) and track their dynamics between 1985 and 2015. Using a Bayesian model, we estimate 28,125 homesteads in 1985 and show that forest smallholders occupy much larger forest areas (>45% of all Chaco forests) than commonly appreciated and increasingly come into conflict with expanding commodity agriculture (18% of homesteads disappeared; n = 5,053). Importantly, we demonstrate an increasing ecological marginalization of forest smallholders, including a substantial forest resource base loss in all Chaco countries and an increasing confinement to drier regions (Argentina and Bolivia) and less accessible regions (Bolivia). Our transferable and scalable methodology puts forest smallholders on the map and can help to uncover the land-use conflicts at play in many deforestation frontiers across the globe. Such knowledge is essential to inform policies aimed at sustainable land use and supply chains.

农业向亚热带和热带森林的扩张造成了重大的环境破坏，但其更广泛的社会影响往往仍然隐藏。以森林为生的小农受到的影响尤其严重，因为他们严重依赖森林资源，通常很穷，而且往往缺乏制度支持。我们的目标是评估与扩大商品农业相关的森林小农动态。我们使用整个南美格兰查科（全球森林砍伐热点）的高分辨率卫星图像，将单个森林小农宅基地数字化（n= 23,954) 并跟踪它们在 1985 年至 2015 年之间的动态。使用贝叶斯模型，我们估计 1985 年有 28,125 个宅基地，并表明森林小农占据的森林面积（占所有查科森林的 45% 以上）比普遍认为的要大得多，并且越来越多地陷入冲突随着商品农业的扩大（18% 的宅基地消失；n= 5,053)。重要的是，我们证明了森林小农的生态边缘化程度越来越高，包括所有查科国家森林资源基础的大量损失以及越来越多的干旱地区（阿根廷和玻利维亚）和交通不便地区（玻利维亚）的限制。我们可转移和可扩展的方法将森林小农放在地图上，并有助于发现全球许多森林砍伐前沿的土地使用冲突。这些知识对于为旨在可持续土地利用和供应链的政策提供信息至关重要。