Abstract
AbstractHedgerows are an abundant and ecologically important feature of many rural areas. Their biodiversity value depends on composition, structure and availability of food resources, which can be significantly impacted by poor management. However, information about hedgerow condition is very limited due to field surveys being costly and labour‐intensive. Unmanned aerial vehicles (UAVs) equipped with miniaturized cameras could prove a more cost‐effective and time‐efficient hedgerow surveying solution while preserving a high level of detail unattainable with airborne or satellite sensors. This study explored whether UAV remote sensing is a viable alternative for performing hedgerow condition surveys at local scale, focusing on hedgerow structure and flowering abundance. We acquired UAV Red, Green and Blue (RGB) and multispectral nadir and oblique imagery of structurally different hedgerows and used them to generate 3D point clouds and models with SfM workflow. Height thresholding allowed extraction of hedgerow extents, with root‐mean‐square error (RMSE) of height and width ranging from 0.11 to 0.23 m. RGB flower classification showed poor relationship with ground measurements (R2 = 0.31–0.42) due to confusion with woody material of hedgerows. Inclusion of a near‐infrared channel in multispectral imagery significantly improved the relationship (R2 = 0.68–0.75, RMSE = 10%). Our study shows UAV remote sensing has high potential for performing detailed surveys of hedgerows, providing better characterization of structural variations and distribution of flowers than traditional ground surveys due to larger coverage. More comprehensive understanding of hedgerow, or other vegetated buffer strips, conditions offered by UAV surveys can enable better informed decisions on habitat management and biodiversity conservation in rural areas. Acquisitions over larger areas, potentially integrated with satellite remote sensing, can allow assessment of hedgerow connectivity over farm to landscape scales, contributing to better understanding of the hedgerow network and its role as a wildlife corridor.
Highlights
Expansion and intensification of agricultural practices has had a negative impact on biodiversity levels in rural areas due to habitat fragmentation, with remnant patches of natural and seminatural land cover being the only safe havens for wildlife
The extracted volumes were smaller for the CHMMICA; the total volume under canopy height models (CHMs) differed by 6.67%–5552.15 m3 as opposed to 5949.00 m3 (Table 2), with the greatest relative difference of 10.98% recorded for hedgerow B1
The root-mean-square error (RMSE) values for both datasets were comparable, with higher errors observed for width estimates for both sensors: 0.11 m/0.14 m for height and 0.18 m/ 0.23 m for width (CHMRGB/CHMMICA)
Summary
Expansion and intensification of agricultural practices has had a negative impact on biodiversity levels in rural areas due to habitat fragmentation, with remnant patches of natural and seminatural land cover being the only safe havens for wildlife Among these are hedgerows, which consist of lines of trees, shrubs, and associated herbaceous understory vegetation. In the British context, hedgerows are typically low, continuous lines of shrubby vegetation, maintained this way through regular trimming. They support flora and provide critical habitat to a wide variety of bird, small mammal, reptile, amphibian and invertebrate species, which depend on a 2021 The Authors. Remote Sensing in Ecology and Conservation published by John Wiley & Sons Ltd
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