Cumulative disturbances to assess forest degradation using spectral unmixing in the northeastern Amazon
Résumé
Question: Tropical forests are subject to disturbances by logging, gathering of fuelwood,
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 northeastern
Amazon.
Methods: We used Landsat annual imagery from 2000 to 2015 and spectral mixture
analysis 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), overlogged forest (no management
plan), overlogged 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,
fuelwood gathering and fire).
Conclusions: The fractional cover of NPV obtained from spectral mixture analysis
can be used to differentiate degradation trajectories and to map forest degradation.
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