This dissertation presents a comparative enviro-colonial history of the northward expansion by Japan and Siam between the late-nineteenth century and the early-twentieth century. The term “enviro-colonial history” connotes the entanglements between environmental history and colonial history that are enabled by the practices of knowledge production and mobilization. In the case of Japan’s colonization of Hokkaido, the promotion of “scientific agriculture” became a means to transform the unfamiliar environment of the northern island into a thriving settler colony for Japanese migrants. Meanwhile, in Siam, the institutionalization of “scientific forestry” was aimed at reconfiguring the relationships around the flourishing timber trade in the northern frontier, to facilitate both the annexation of the Lanna states and the centralization of forest regulation. As I will elaborate in the chapters that follow, the production and mobilization of agricultural science in Hokkaido and forestry in Lanna enabled the imagination of “enviro-colonial rule” – a form of governance that entangled environmental management with colonial administration as if they were part of the same process.