If global policies intended to promote forest conservation continue to use the definition of “forest” adopted in 2001 by the United Nations Framework Convention on Climate Change (an area of >0.05–1 ha with >10–30% cover of plants >2–5 m tall at maturity), great quantities of carbon and other environmental values will be lost when natural forests are severely degraded or replaced by plantations but technically remain “forests.” While a definition of “forest” that is globally acceptable and appropriate for monitoring using standard remote sensing options will necessarily be based on a small set of easily measured parameters, there are dangers when simple definitions are applied locally. At the very least, we recommend that natural forest be differentiated from plantations and that for defining “forest” the lower height limit defining “trees” be set at more than 5 m tall with the minimum cover of trees be set at more than 40%. These changes will help reduce greenhouse gas emissions from what is now termed forest “degradation” without increasing monitoring costs. Furthermore, these minor changes in the definition of “forest” will promote the switch from degradation to responsible forest management, which will help mitigate global warming while protecting biodiversity and contributing to sustainable development.

In May 2014, the Member States of the United Nations adopted Resolution 23/1 on “strengthening a targeted crime prevention and criminal justice response to combat illicit trafficking in forest products, including timber.” The resolution promotes the development of tools and technologies that can be used to combat the illicit trafficking of timber. Stopping illegal logging worldwide could substantially increase revenue from the legal trade in timber and halt the associated environmental degradation, but law enforcement and timber traders themselves are hampered by the lack of available tools to verify timber legality. Here, we outline how scientific methods can be used to verify global timber supply chains. We advocate that scientific methods are capable of supporting both enforcement and compliance with respect to timber laws but that work is required to expand the applicability of these methods and provide the certification, policy, and enforcement frameworks needed for effective routine implementation.