In the battle to address Europe’s biodiversity crisis, fixing its implementation gap—the gap between EU nature law on the books, and on the ground—is vital. Europe’s private nature governance revolution, underpinned by the UNECE Aarhus Convention, is a core part of its response. This article breaks new empirical ground in understanding how those mechanisms have been working in practice, and their knock-on effects for traditional enforcement by the State. We develop an innovative methodological tool, the Nature Governance Effectiveness Indicators (“NGEIs”), enabling the first quantitative measurement of the effectiveness of public and private nature governance in practice. In collecting data on these indicators, we create a novel dataset spanning three jurisdictions and 23 years, giving a unique insight into Europe’s “environmental democracy in action”. We regress the NGEIs against the Nature Governance Index, an original longitudinal index measuring the evolution in nature governance laws over this period. Our results provide the first systematic empirical evidence that, despite the widespread embrace of private nature governance laws on the books across our studied jurisdictions from 1992 to 2015, the enhanced citizens’ rights conferred by these laws are not being consistently used in practice. They also reveal that, despite these inconsistencies in usage of the Aarhus mechanisms in practice, passing private governance laws can in fact improve levels of State enforcement of EU nature law in practice. For policymakers seeking to increase enforcement of EU nature law on the ground, harnessing what we term the shadow of heterarchy, by strengthening private governance rights, may therefore be a more effective means of doing so than simply ratcheting up existing traditional governance mechanisms such as levels of maximum criminal penalties or civil fines.