Fifteen operationally important decisions in the planning of biodiversity offsets

Many development projects, whether they are about construction of factories, mines, roads, railways, new suburbs, shopping malls, or even individual houses, have negative environmental consequences. Biodiversity offsetting is about compensating that damage, typically via habitat restoration, land management, or by establishment of new protected areas. Offsets are the fourth step of the so-called mitigation hierarchy, in which ecological damage is first avoided, minimized second, and third restored locally. Whatever residual damage remains is then offset. Offsetting has been increasingly adopted all around the world, but simultaneously serious concerns are expressed about the validity of the approach. Failure of offsetting can follow from either inappropriate definition of the size and kind of offset, or, from failure in implementation. Here we address planning of offsets, and identify fundamental operational design decisions that define the intended outcome of an offsetting project, and organize these decisions around objectives, offset actions, and the three fundamental ecological axes of ecological reality: space, time and biodiversity. We also describe how the offset ratio of a project (size of offset areas compared to impact area) can be constructed based on several partial multipliers that arise from factors such as degree of compensation required relative to no net loss, partial and delayed nature of restoration or avoided loss gains, time discounting, additionality, leakage, uncertainty, and factors associated with biodiversity measurement and offset implementation. Several of these factors are partially subjective and thus negotiable. The overall purpose of this effort is to allow systematic, well informed and transparent discussion about these critical decisions in any offset project.peerReviewe