Emmert, L.; Negrón-Juárez, R.I.; Chambers, J.Q.; Santos, J.D.; Lima, A.J.N.; Trumbore, S.; Marra, D.M. Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest. Remote Sens.2023, 15, 4027.
Emmert, L.; Negrón-Juárez, R.I.; Chambers, J.Q.; Santos, J.D.; Lima, A.J.N.; Trumbore, S.; Marra, D.M. Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest. Remote Sens. 2023, 15, 4027.
Emmert, L.; Negrón-Juárez, R.I.; Chambers, J.Q.; Santos, J.D.; Lima, A.J.N.; Trumbore, S.; Marra, D.M. Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest. Remote Sens.2023, 15, 4027.
Emmert, L.; Negrón-Juárez, R.I.; Chambers, J.Q.; Santos, J.D.; Lima, A.J.N.; Trumbore, S.; Marra, D.M. Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest. Remote Sens. 2023, 15, 4027.
Abstract
Windthrow (i.e., trees broken and uprooted by wind) is a major natural disturbance in the Amazon. Images from medium-resolution optical satellites (mostly Landsat) combined with extensive field data have allowed researchers to assess patterns of tree mortality and monitor forest recovery over decades of subsequent succession in different regions. Although satellites with high spatial-resolution have become available for the Amazon in the last decade, they have not yet been employed for the mapping and quantification of windthrow tree-mortality. Here, we address how increasing the spatial resolution of satellites affects plot-to-landscape estimates of windthrow tree-mortality. We combined forest inventory data with Landsat 8 (30 m pixel), Sentinel 2 (10 m), and WorldView 2 (2 m) imagery over an old-growth forest in the Central Amazon that was disturbed by a single windthrow event in November/2015. Remote sensing estimates of tree mortality were produced with Spectral Mixture Analysis and analyzed together with forest inventory data using Generalized Linear Models. Windthrow tree-mortality measured in 3 transects (30 subplots) crossing the entire disturbance gradient was 26.9 ± 11.1% (mean ± 95% CI). Based on this ground truth, the three satellites produced reliable and statistically similar estimates (from 26.5% to 30.3% windthrow tree-mortality, p<0.001). The mean-associated uncertainties decreased systematically with increasing spatial resolution (i.e., from Landsat 8 to Sentinel 2 and WorldView 2). However, the overall quality of fit of models showed the opposite pattern, which may reflect the influence of crown damage not accounted for in our field study, and fast-growing regeneration of leaf area. Among the satellites studied, Landsat 8 most accurately captured field observations of variations in tree mortality across the disturbance gradient (i.e., lower under- and/or overestimation from undisturbed to extremely damaged forest). Although satellites with high spatial-resolution can refine estimates of windthrow severity by allowing the quantification of individual tree damage and mortality, our results validate the reliability of Landsat imagery for assessing patterns of windthrow tree-mortality in dense and heterogeneous tropical forests. Although high-resolution imagery may improve estimates of tree damage and mortality, these should be validated using field data at compatible scales.
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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