Abstract Biodiversity offsetting is usually the last step in the mitigation hierarchy and aims to compensate for impacts of development projects on biodiversity. It is supposed to contribute to the key environmental objective of “no net loss” of biodiversity by delivering gains equivalent to losses. We hypothesize that such gains can only be attained through ecological restoration of degraded sites: the restored ecosystem should not only equal the original or reference ecosystem as usually assumed, but rather the original state of degradation of the ecosystem used for offsetting should be of the same level as the impacted ecosystem after development. We built on this starting assumption to determine whether impacts and gains were considered equally in the offsetting measures of 24 infrastructure projects, and to infer the potential gains in offset sites, based on an analysis of procedure and administrative documents. The analysis showed that impacts were presented in much more detail than the offsetting measures. In addition, out of 577 ha that was intended to offset areas being artificialized, only 3% of the area was artificial prior to offsetting work, i.e. delivering high potential gains, while 81% could be considered semi-natural habitats, thus with lower potential gains. Little information on the ecological quality of offset sites was available. When described, their good quality was used as an argument to justify their selection, resulting in relatively uncertain gains in comparison to certain impacts. Our results suggest that including multiple comparisons of multiple ecosystem states is a way forward to better evaluate the equivalence between gains and losses, and thus would ensure no net loss of biodiversity.

中文翻译：

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生物多样性抵消：净损失的确定性但净收益的不确定性

摘要 生物多样性抵消通常是缓解层次结构的最后一步，旨在补偿开发项目对生物多样性的影响。它应该通过提供与损失相当的收益来促进生物多样性“无净损失”的关键环境目标。我们假设只有通过退化场地的生态恢复才能获得这种收益：恢复的生态系统不仅应该与通常假设的原始或参考生态系统相同，而且用于抵消的生态系统退化的原始状态应该是相同的水平作为开发后受影响的生态系统。我们以此初始假设为基础，确定在 24 个基础设施项目的抵消措施中是否平等考虑影响和收益，并根据对程序和行政文件的分析推断抵消地点的潜在收益。分析表明，影响比抵消措施更详细。此外，在旨在抵消人工化区域的 577 公顷中，只有 3% 的面积在抵消工作之前是人工的，即提供高潜在收益，而 81% 可被视为半自然栖息地，因此潜力较低收益。关于抵消点生态质量的信息很少。在描述时，它们的良好质量被用作证明其选择合理的论据，导致与某些影响相比相对不确定的收益。