Historical Declines in Semi-Natural Habitat Across an Agricultural Landscape Drive Modelled Losses in Wild Bee Abundance

Agricultural intensification contributed to a general reduction in woodlands, grasslands, and hedgerows across farmed landscapes in the latter half of the 20th century. These semi-natural habitats are important resources for biodiversity, and their decline is linked with observed losses in pollinator abundance and species richness.We used Copernicus Sentinel-2 satellite data and historical maps to estimate land-use change across the Leighfield Forest region of the United Kingdom between 1952 and the present-day. Our analysis suggests that the region has lost 76% of its hedgerows and 44% of its grassland habitats, while arable areas have increased six-fold. Average field sizes increased from 6.74 ha to 7.42 ha in the same period.Wild bee abundance and species richness were recorded in a stratified survey campaign during the spring and summer of 2020. 49 different species were recorded in the surveys. Field-observed abundance was compared against the Integrated Valuation of Ecosystem Service Trade-offs and Synergies (InVEST) pollinator model. InVEST was able to predict field-observed abundance of ground nesting bumblebees (R2 = 0.41, p < 0.001), tree nesting bumblebees (R2 = 0.42, p < 0.001), and ground nesting solitary bees (R2 = 0.31, p < 0.001) in the modern landscape, but was not able to predict the abundance of cavity nesting solitary bees. The InVEST pollinator model was sensitive to changes in the abundance of semi-natural habitat, with field boundary habitats having the greatest overall effect on the model’s abundance index.We estimated wild bee abundance in the historical landscape for all four guilds by assuming that this is controlled exclusively by habitat availability (i.e., ignoring other pressures on pollinators such as climate change, pesticide use, and mite infestation). The average modelled abundance index decreased by 32% over the study period suggesting that losses in semi-natural habitat over the last 70 years have been a major contributor to declines in the region’s population of wild bees. Losses associated with hedgerow removal were mitigated when the surrounding habitat was kept in pasture, compared with areas where hedgerows were removed, and the surrounding landscape transitioned from pasture to arable land cover.These findings support the case for replanting hedgerows, maintaining botanically diverse pasture, incorporating long-term grass/clover leys into arable rotations, and creating flower-rich habitats to reverse pollinator declines in agricultural landscapes.