A lidar based national model of hedgerows and other woody linear features in rural England

Hedgerows and other woody linear features (WLF) are important semi-natural habitats, cultural features and potential carbon stores in farmland across several regions of the world, particularly Western Europe. Monitoring WLF has been limited by difficulties of mapping their extent and dimensions at large scales. Remote sensing can overcome such limitations by mapping WLF at high resolution at the national scale, but examples are few and generally more localized. We tested whether openly available, 1 m² resolution lidar could be used within a high-performance computing environment to model the extent and height of the WLF coverage in England. The results were compared with comprehensive ground truthing within 248 × 1 km² sample squares. There was close agreement (99.7 %) between the mean and total extent of WLF from the model and ground truthing squares, with 74 % of modelled WLF showing close alignment (<20 m distance) with ground truthed WLF. Total length of WLF in England was estimated as 641,079.8 km, with 29 % composed of trees/bushes taller than 6 m, and 61 % (389,439.3 km) corresponding to managed hedgerows of 1-6 m tall. Precise agreement between height classes in the model and sample squares was more modest (36 % of WLF lengths), but higher (60 %) if allowing a tolerance of ±1 height class for matching to accommodate temporal differences between lidar collection (2016-2021) and ground truthing (2022-2023). The model represents a significant improvement in mapping and monitoring WLF using openly available national lidar, and the limitations and potential opportunities are discussed.