In reaction to Greenpeace campaigns denouncing the impact of oil palm plantations in Southeast Asia, Golden Agri-Resources (GAR) – a major actor in the palm oil sector – adopted a zero-deforestation policy. The implementation of this policy raised a simple, albeit tricky, question: what is a forest? In response, Greenpeace, GAR and a consultancy firm developed a methodology for forest classification called the High Carbon Stock (HCS) Approach. Employing a vegetation classification based primarily on a threshold of carbon sequestration, the method identifies which forested zones to protect from conversion to agriculture. While currently gaining resonance in the realm of sustainability standards, its implementation in Indonesia and Liberia encountered resistance and criticism by rural dwellers and social NGOs. How did HCS advocates integrate local peoples’ concerns, interests and claims to compose commonality? By analysing the HCS methodology's content, implementation and progressive adaptation, this article shows how HCS advocates favoured a specific mode of composition: one that fits a liberal grammar and that has specific implications on the valuation of forest and cultivable lands. The HCS approach is thus more than a data collection tool; it encapsulates and reinforces a particular vision of the environment and how people should relate to it.