An assessment of the accuracy of satellite-derived woody and grass foliage cover estimates for Australia

Context Understanding the functional role of vegetation across landscapes requires the ability to monitor tree and grass foliage cover dynamics. Several satellite-derived products describe total and woody foliage cover across Australia. Few of these are suitable for monitoring changes in woody foliage cover and only one can currently describe subseasonal dynamics in both woody and grass cover. Aims (1) To improve the accuracy of woody and grass foliage cover estimates in Australia's arid environments, around major disturbances and in perennially green pastures. (2) To gain a detailed understanding of the accuracy of woody and grass foliage cover estimates for Australia. Methods Satellite-derived greenness data were converted to total foliage cover fraction (0.0-1.0), accounting for differences in background soil affects. Total cover was split into component woody and grass cover by using a modified persistent-recurrent splitting algorithm. Results were compared with 4214 field measurements of cover. Key results Accuracy varied between woody and grassland vegetation types, with total, woody and grass foliage cover having low errors (of similar to 0.08) and near-zero biases across all woody vegetation types. Across grasslands, errors were higher (up to 0.28), and biases were greater (and negative), with both scaling with foliage density. Conclusions Foliage cover was accurately estimated for forested through to sparsely wooded ecosystems. Foliage cover of pure, dense grasslands was systematically underpredicted. Implications This is the only Australian cover product that can generate temporally dense woody and grass foliage cover data and is invaluable for monitoring vegetation dynamics, particularly across Australia's mixed tree-grass landscapes.