Abstract
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.
Highlights
Disturbances caused by windthrows or insect outbreaks play an immanent role in the dynamics of most forest ecosystems (Franklin et al, 2002; Turner et al, 1998)
For HH and HV polarizations, Radar change ratios (RCR) indices indicated statistically significant changes compared to pre-event conditions, except for the dataset acquired under wet conditions (2007.05.18)
The variable RCR values over stable areas are the result of variations in environmental conditions at the acquisition of Dynamic range
Summary
Disturbances caused by windthrows or insect outbreaks play an immanent role in the dynamics of most forest ecosystems (Franklin et al, 2002; Turner et al, 1998). In temperate forests, insect outbreaks and severe weather conditions can affect 50 times as much forest area as fires (Dale et al, 2001). Windthrows and insect outbreaks are influenced by global change in several ways (Schlyter et al, 2006). Extreme climate events in combination with a higher mean temperature decrease forest vitality, which in turn increases forest susceptibility to windthrows. Windthrows, in turn, often trigger insect outbreaks, which are facilitated by warm and dry weather conditions (Seidl et al, 2016). Future climate projections predict that disturbances will further intensify (Seidl et al, 2014; Westerling et al, 2006), with potentially major impacts on global carbon sequestration (Kurz et al, 2008). Early detection could support timely salvage logging operations and thereby minimize economic losses (Fahse and Heurich, 2011), or could allow short-term actions aimed at reducing the ecological impact of disturbance
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