Quantifying biodiversity benefits of woody plantings on Tasmanian farms for natural capital accounting

Newly emerging market mechanisms hold significant potential to accelerate investment in restoring biodiversity, but data and tools to account for biodiversity gains constrain their implementation. To address this challenge, we quantified habitat characteristics and plant biodiversity of 56 agroforestry and revegetation plantings in Tasmanian agricultural landscapes, hypothesizing that outcomes would depend on biodiversity measure, planting type, and age of planting. We demonstrated the application of these data to a natural capital accounting framework by expressing biodiversity stocks in pastures and plantings as proportions of those in natural reference forests, and the biodiversity benefits (biodiversity gains) as changes to stocks over time. Results showed significant, age‐dependent increases in habitat characteristics that potentially support biodiversity, leading to mean habitat scores of 0.33–0.43 of reference values in 20‐year‐old plantings. Native plant species cover and richness in native plantings reached up to 0.35 of reference, but these largely reflected species planted, and no benefits were detected for native ground‐layer plants or in exotic plantings. Further, benefits estimated using native plant species compositional similarity were less than half of those estimated using plant species richness or cover. We conclude that while plantings offer potential fauna habitat, they are not readily recolonized by native plants, and additional understorey restoration to intensify biodiversity benefits would be worthwhile. Our analyses demonstrate the calculation of factors and models to estimate the potential biodiversity benefits of different types of plantings in an accounting context, and emphasize the importance of the choice of measure in accounting for gains.