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Background on Disturbances

Concept Behind
GEDS Detection

Entry to GEDS Results

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Concept Behind GEDS Detection
Leafy vegetation cover is likely the most fragile and therefore perhaps the single most vulnerable biotic component of terrestrial ecosystems to detectable alteration during disturbance events. Vegetation leaf cover burns relatively easily or can be readily blown down or cut to the ground. Leaf litter then decomposes rapidly to blend in with background soil attributes.

Earth-observing satellites have monitored leafy vegetation cover over the globe, also called 'greenness' cover, for over 20 years. A common measure of greenness cover is the fraction of photosynthetically active radiation, or FPAR, intercepted by vegetation canopies. FPAR ranges from zero (on barren land) to 100% (for the densest plant cover). In theory, the higher the FPAR level observed over the course of a seasonal plant growing cycle, the denser the green leaf cover and (presumably, on average) the less disturbed the vegetation cover, and/or the longer the time period since the last major disturbance. Research has shown that any significant and sustained decline in vegetation FPAR observed from satellites likely represents a disturbance event. All new disturbance events are, however, subject to verification from independent observational records of such events. For scientific journal references to the GEDS methods and results, click here.

Examples of documented disturbance events represented in the GEDS time series record include the following…

Top panels are original (raw) FPAR values over the period 1982-2000, whereas the bottom panels are the deseasonalized FPAR anomalies in units of standard deviation (SD) in the 12-month moving average. Vertical lines show the longest consecutive period of anomalously LO monthly values detected. Owing to the use of a moving average, the apparent start time of the FPAR-LO events shown in the bottom panels may be up to 12-months shifted from the documented timing of the disturbance event. Latitude is shown in decimal degrees N, and longitude in decimal degrees W.

 

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