Biodiversity Intactness Index Calculator

The Biodiversity Intactness Index is a metric that measures how intact local ecosystems are compared to their natural, undisturbed baseline. A BII of 100% means biodiversity is fully intact, while lower scores indicate progressive ecological disruption due to land use change, habitat loss, or other pressures. It was originally proposed in 2005 and developed using the PREDICTS database by the Natural History Museum.

Scientists consider a BII below 90% to represent a significant ecological threshold, beyond which ecosystems may struggle to maintain their functions and resilience. Many regions globally now fall below this level due to agricultural expansion and urbanisation. The Kunming-Montreal Global Biodiversity Framework (GBF) uses BII as a complementary indicator to monitor progress on biodiversity goals.

BII is the product of two components: Total Abundance (the average abundance of originally-present species relative to a pristine baseline) and Compositional Similarity (a measure of how similar the current species community is to the original community in composition). Both components are affected by land use type and intensity.

Urban areas and intensive cropland typically cause the greatest biodiversity loss, with very low abundance and compositional similarity factors compared to primary vegetation. Pasture and secondary vegetation represent intermediate disturbance levels, while primary vegetation retains the highest intactness. The biome type also influences sensitivity — tropical forests host more endemic species and are especially vulnerable.

PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) is a global database that aggregates biodiversity data from hundreds of studies comparing species abundance and composition at sites under different land uses versus undisturbed reference sites. It forms the empirical backbone of BII calculations produced by the Natural History Museum.

This simplified calculator estimates BII based on land use proportions, biome type, and disturbance intensity — key drivers that correlate with fragmentation effects. Full scientific BII calculations also incorporate spatial fragmentation metrics and species-level data from the PREDICTS database, which require GIS raster data and statistical modelling beyond the scope of a web calculator.

This calculator provides an educational estimate based on published land-use abundance and similarity coefficients. It does not incorporate site-level species data, spatial connectivity, invasive species effects, or climate projections. For policy-grade BII assessments, use the Natural History Museum's Biodiversity Trends Explorer or the BON in a Box pipeline with full PREDICTS data.

Restoring degraded land to secondary or primary vegetation, reducing agricultural intensification, protecting remaining primary habitats, and reducing urban sprawl all increase BII. Even partial restoration of cropland or pasture to secondary vegetation can meaningfully raise abundance and compositional similarity scores over time.