The Convention on Biological Diversity’s Aichi Target 11 calls for 17% of terrestrial and 10% of marine areas to be in “effective and equitably managed, ecologically representative and well connected” protected areas by 2020. This is one of many global and national conservation policies that require progress reporting towards achieving conservation targets. Transparent and repeatable metrics that can be applied broadly are an important step towards meeting these commitments. Currently the most widely used approach for evaluating progress towards these goals is reporting total protected area coverage due to its relatively unambiguous and easily quantifiable nature. However, this alone is not a sufficient indicator for conservation achievement because it ignores the other key components of conservation target, such as how well a network represents important biodiversity features (e.g. ecological regions or species). While reporting the number or percentage of ecoregions that meet a protected area coverage target has been a first attempt towards this end, such measures ignore biodiversity features that do not reach a target but still provide some degree of protection.
Building on the work by Sutcliffe et al. , we present two complementary metrics measuring ecological representation for protected area networks. The ‘mean protection gap’ (MPG) and the ‘mean target achievement’ (MTA) determine the degree of conservation target shortfall or achievement in a single metric and thus show a more differentiated picture of the state and progress in protected area coverage beyond reporting total protection level or amount of features that reach a target alone. To facilitate use of these metrics by researchers and conservation practitioners we have developed an R package to calculate and plot both metrics.
We use Australia’s proposed Commonwealth Marine Reserve network as a case study to demonstrate the application of these metrics. Our case study showcases that the network would be praised by reporting total area protected alone, as it surpasses the 10% target of Aichi 11 four-fold with 43% of the marine area protected. However, the MPG and MTA metrics highlight shortfalls in the protection of several bioregions that would remain undetected if only the overall level of protection were considered. Additionally, MPG and MTA account for considerable, yet underperforming protection levels that are missed in other standard reporting measures, but contribute to overall biodiversity goals. We recommend these metrics be used to evaluate progress towards building representative protected area networks in line with Aichi target 11’s goals.
 Sutcliffe P.R., Klein C.J., Pitcher C.R., Possingham H.P. (2015) The effectiveness of marine reserve systems constructed using different surrogates of biodiversity. Conservation Biology 29, 657-667.