PDF(Pubmed)
Abstract：
Biodiversity offsetting is a globally influential policy mechanism for reconciling trade-offs between development and biodiversity loss. However, there is little robust evidence of its effectiveness. We evaluated the outcomes of a jurisdictional offsetting policy (Victoria, Australia). Offsets under Victoria\'s Native Vegetation Framework (2002-2013) aimed to prevent loss and degradation of remnant vegetation, and generate gains in vegetation extent and quality. We categorised offsets into those with near-complete baseline woody vegetation cover (\"avoided loss\", 2702 ha) and with incomplete cover (\"regeneration\", 501 ha), and evaluated impacts on woody vegetation extent from 2008 to 2018. We used two approaches to estimate the counterfactual. First, we used statistical matching on biophysical covariates: a common approach in conservation impact evaluation, but which risks ignoring potentially important psychosocial confounders. Second, we compared changes in offsets with changes in sites that were not offsets for the study duration but were later enrolled as offsets, to partially account for self-selection bias (where landholders enrolling land may have shared characteristics affecting how they manage land). Matching on biophysical covariates, we estimated that regeneration offsets increased woody vegetation extent by 1.9%-3.6%/year more than non-offset sites (138-180 ha from 2008 to 2018) but this effect weakened with the second approach (0.3%-1.9%/year more than non-offset sites; 19-97 ha from 2008 to 2018) and disappeared when a single outlier land parcel was removed. Neither approach detected any impact of avoided loss offsets. We cannot conclusively demonstrate whether the policy goal of \'net gain\' (NG) was achieved because of data limitations. However, given our evidence that the majority of increases in woody vegetation extent were not additional (would have happened without the scheme), a NG outcome seems unlikely. The results highlight the importance of considering self-selection bias in the design and evaluation of regulatory biodiversity offsetting policy, and the challenges of conducting robust impact evaluations of jurisdictional biodiversity offsetting policies.
摘要：
生物多样性补偿是一种具有全球影响力的政策机制，用于协调发展与生物多样性丧失之间的权衡。然而,几乎没有有力的证据证明它的有效性。我们评估了管辖权抵消政策的结果(维多利亚，澳大利亚)。根据维多利亚州的本地植被框架（2002-2013）的偏移，旨在防止残留植被的损失和退化，并在植被范围和质量上产生收益。我们将偏移量归类为具有接近完整基准木本植被覆盖的偏移量（“避免损失”，2702公顷)且覆盖不完整(“再生”，501公顷)，并评估了2008年至2018年对木本植被范围的影响。我们使用了两种方法来估计反事实。首先,我们在生物物理协变量上使用了统计匹配：保护影响评估中的一种常用方法，但有可能忽视潜在的重要的心理社会混杂因素。第二,我们将偏移的变化与研究期间未偏移但后来作为偏移登记的部位的变化进行了比较。部分考虑到自我选择偏差(土地所有者登记土地可能具有影响他们如何管理土地的共同特征)。匹配生物物理协变量，我们估计，再生补偿增加了1.9%-3.6%/年比非补偿场地（从2008年到2018年为138-180公顷），但这种影响在第二种方法中减弱（0.3％-1.9%/年比非补偿场地多；从2008年到2018年为19-97公顷），当单个异常地块被移除时消失。两种方法都没有检测到避免的损失补偿的任何影响。由于数据限制，我们无法最终证明是否实现了“净收益”（NG）的政策目标。然而,鉴于我们的证据表明，木本植被的大部分增加并不是额外的（如果没有该计划，就会发生），NG结果似乎不太可能。结果突出了在监管生物多样性抵消政策的设计和评估中考虑自我选择偏差的重要性，以及对管辖权的生物多样性抵消政策进行强有力的影响评估的挑战。
