Detection of windthrows and insect outbreaks by L-band SAR: A case study in the Bavarian Forest National Park

Natural disturbances significantly influence forest ecosystem services and biodiversity. Accurate delineation and early detection of areas affected by wind and insect outbreaks are crucial for guiding management decisions. To this end, past studies relied mostly on passive sensors (e.g., optical), and active sensors (i.e., radar) were rarely used. This study used L-band space-borne synthetic aperture radar (SAR) within a change-detection framework to delineate forested areas affected by wind and insect disturbances. The results showed that changes in backscatter relate to damage caused by wind and insect outbreaks. Overall accuracies of 69–84% and 65–88% were obtained for delineation of areas affected by wind damage and insect outbreaks, respectively, depending on the acquisition date and environmental conditions. Areas susceptible to insect outbreaks or experiencing the initial outbreak phase (green) were detected with lower accuracies (64–74%). It is expected that L-band space-borne SAR data can be applied over larger areas and ecosystem types in the temperate and boreal regions to delineate and detect damaged areas. •A first analysis of insect outbreaks using L-band data is established.•SAR-based change detection is adopted, adapted, and used over affected areas.•Accuracies up to 90% were observed depending on disturbance agent and timing.•Thresholding and machine learning classification results were similar.•Early detection of insect outbreaks (one-year lead time) was demonstrated.