Outcomes from 10 years of biodiversity offsetting

Abstract

We quantified net changes to the area and quality of native vegetation after the introduction of biodiversity offsetting in New South Wales, Australia-a policy intended to "prevent broad-scale clearing of native vegetation unless it improves or maintains environmental values." Over 10 years, a total of 21,928 ha of native vegetation was approved for clearing under this policy and 83,459 ha was established as biodiversity offsets. We estimated that no net loss in the area of native vegetation under this policy will not occur for 146 years. This is because 82% of the total area offset was obtained by averting losses to existing native vegetation and the rate that these averted losses accrue was over-estimated in the policy. There were predicted net gains in 10 of the 14 attributes used to assess the quality of habitat. An overall net gain in the quality of habitat was assessed under this policy by substituting habitat attributes that are difficult to restore (e.g. mature trees) with habitat attributes for which restoration is relatively easy (e.g. tree seedlings). Long-term rates of annual deforestation did not significantly change across the study area after biodiversity offsetting was introduced. Overall, the policy examined here provides no net loss of biodiversity: (i) many generations into the future, which is not consistent with intergenerational equity; and (ii) by substituting different habitat attributes, so gains are not equivalent to losses. We recommend a number of changes to biodiversity offsetting policy to overcome these issues.

The ecological outcomes of biodiversity offsets under “no net loss” policies: A global review

“…All seven used change in habitat area as outcome variables, and reported results from offset programs focused predominantly on habitat creation and restoration (BenDor, Brozovic, & Pallathucheril, , ; Breaux et al., ; Harper & Quigley, ; Kettlewell et al., ; Kozich & Halvorsen, ; Robertson & Hayden, ). The other three studies also using area as their outcome variables that failed to achieve NNL were all reporting results from offset systems based predominantly on avoided loss offsets (Gibbons et al., ; Goldberg & Reiss, ; Morgan & Roberts, ). The remaining studies evaluated the success of bat mitigation in the United Kingdom under the objective of “NNL in local bat population status,” and the percentage of offset sites in Isère, France, where the required offset habitat type or species was present.…”

“…This can be justified as a mechanism for preventing biodiversity loss if the background rate of biodiversity loss is sufficiently high. However, in the studies included here and the wider literature, it is evident that assumed rates of background declines are commonly higher than the actual rate, superficially justifying the use of avoided loss offsets when in reality gains only accrue many decades into the future (Gibbons et al., ; Reside et al., ). This issue is compounded if the “protection” afforded by offsets does not actually reduce the probability of loss, most commonly when sites that are not under threat of development receive “protection” (e.g., Thorn et al., ).…”

“…Avoided loss offsets appeared to be unsuccessful for multiple reasons. Critically, they necessarily lead to an immediate net loss in habitat area (Gibbons et al., ). This can be justified as a mechanism for preventing biodiversity loss if the background rate of biodiversity loss is sufficiently high.…”

“…For example, in Florida between 2001 and 2011, mitigation banking restored 58,575 ha of wetlands, yet across the state, a net 5600 ha/year was lost during the same time period (Levrel et al., ), which is possibly because the Clean Water Act applies only to “jurisdictional wetlands,” thus many wetland impacts escape regulation. Discrepancies between the apparent success of program‐scale area‐based evaluations and landscape‐scale ones indicate that NNL policies are likely undermined if some impacts are unreported or otherwise exempt from regulation (Gibbons et al., ; Reside et al., ). Thus, the scope of impacts falling underneath these policies should be widened to include all impacts and minimize opportunities to avoid NNL legislation.…”

“…Combined, these points emphasise the need for higher‐quality evidence to understand when NNL is defensible as a conservation strategy. Our review identified just one study meeting our inclusion criteria that compared NNL outcomes with a robust counterfactual (Gibbons et al., ). Generally, the quality of impact evaluations for NNL appear to be lagging behind those applied in other areas of conservation and environmental policy, such as payments for ecosystem services (Pynegar, Jones, Gibbons, & Asquith, ), protected areas (Miteva, Pattanayak, & Ferraro, ), commodity sustainability certification (Carlson et al., ), and forest policy (Simmons et al., ).…”