Building references for nature conservation

Abstract Conservation references have long been used in conservation biology to compare current biodiversity processes and states with past conditions. However, beyond the paucity of data for the construction of ancient, even prehuman, references, the relevance of these ancient references for studying ecosystems radically modified by human activities is questionable, particularly when the notions of conservation references and conservation objectives are confused and when several conservation ethics coexist that require distinct references. Because of this implicit heterogeneity in the nature of the references and their temporal baseline, conservation references not only have different meanings, but also deliver different messages. I propose establishing a common framework for conservation references to approach past biological systems and build comparable references between studies and projects. The selection of these references (distinct from conservation objectives) should be an early, explicit, standardized, and transparent milestone in any conservation process and these references should be based on state, pressure, or process dynamics, rather than fixed states. Finally, the importance of the diversity of temporal baselines used to build conservation references and to measure anthropogenic impacts should be recognized to understand the biodiversity crisis in its entirety.