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Cumulative disturbances to assess forest degradation using spectral unmixing in the north-eastern Amazon

Hasan A.F., Laurent F., Messner F., Bourgoin C., Blanc L.. 2019. Applied Vegetation Science, 22 (3) : p. 394-408.

DOI: 10.1111/avsc.12441

Question: Tropical forests are subject to disturbances by logging, gathering of fuel wood, and fires. Can degradation trajectories (i.e. cumulative disturbances events over a period of timer) be identified using remote sensing Landsat time series?. Location: Paragominas (Pará, Brazil), a municipality covering 19 395 km² in the north-eastern Amazon. Methods: We used Landsat annual imagery from 2000 to 2015 and spectral mixture analysis developed by Asner (2006) to derive time series of the fraction of soil (S), active photosynthetic vegetation (PV), and non-photosynthetic vegetation (senescent) (NPV) indicators. Results: The NPV values over a 16 year period revealed five different degradation trajectories (i.e. cumulative disturbances in space and over time): undisturbed forest, selectively logged forest (with a management plan), over logged forest (no management plan), over logged forest (charcoal production) and burned forest. The variance of NPV calculated per pixel over the same period is useful to map forest degradation over Paragominas municipality, highlighting the role of disturbance factors (logging, fuel wood gathering and fire). Conclusions: The fractional cover of NPV obtained from spectral mixing analysis can be used to differentiate degradation trajectories and to map forest degradation.

Mots-clés : forêt; forêt tropicale; cartographie des fonctions de la forêt; télédétection; déboisement; impact sur l'environnement; amazonie; brésil

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