Assessing the use of Geoscience Laser Altimeter System data to quantify forest structure change resultant from large-scale forest disturbance events- Case Study Hurricane Katrina Details
The biodiversity, structure, and functioning of forest systems in most areas are strongly influenced by disturbances. Forest structure can both influence and help indicate forest functions such as the storage and transfer of carbon between the land surface and the atmosphere. A 2007 report published by the National Research Council states that ‘Quantifying changes in the size of the [vegetation biomass] pool, its horizontal distribution, and its vertical structure resulting from natural and human-induced perturbations, such as deforestation and fire, and the recovery processes is critical for measuring ecosystem change.’ This study assessed the use of the Geoscience Laser Altimeter System (GLAS) to detect and quantify changes in forest structure caused by Hurricane Katrina. Data from GLAS campaigns for the year proceeding and following Katrina were compared to wind speed, forest cover, and damage maps to analyze sensor sampling, and forest structure change over a range of spatial scales. Results showed a significant decrease in mean canopy height of 4.0 m in forested areas experiencing category two winds, a 2.2 meter decrease in forests experiencing category one winds, and a 0.6 meter change in forests hit by tropical storm winds. Changes in structure were converted into carbon estimates using the Ecosystem Demography (ED) model to yield above ground carbon storage losses of ~30Tg over the domain. Although the greatest height loss was observed in areas hit by category two winds, these areas only contributed to a fraction (~3Tg) of the estimated above ground carbon storage losses resultant from Katrina, highlighting that small disturbance spread over a large area can account for as much as or more damage than intense disturbance over smaller areas. This finding stresses the importance of detecting and measuring the full extent of storm damage. While results highlighted the potential use of space-born Lidar in damage detection and quantification, they also emphasize limitations on the scope and scale at which current data can quantify hurricane related changes. Season of data acquisition was shown to influence calculations of mean canopy height and change. Limited sampling hindered our ability to make reliable estimates of height change and standing biomass loss at one degree resolution and smaller across the domain. These results have implications for sampling requirements in upcoming missions, such as DESDnyI, that will improve our ability to detect and quantify forest structure changes from disturbance events.
EOS, Transactions American Geophysical Union, Fall Meeting, Supplement
American Geophysical Union Publications
Dolan, K., Hurtt, G., Chambers, J., Dubayah, R., Frolking, S. and Masek, J. (2009), Assessing the use of Geoscience Laser Altimeter System data to quantify forest structure change resultant from large-scale forest disturbance events- Case Study Hurricane Katrina, Eos Trans. AGU, 90(52), Fall Meet. Suppl., Abstract B31A-0331.