INTEGRATED NDVI AND INUNDATION IN A SKY LAKE, MISSISSIPPI, BALD CYPRESS STAND

We examined the relationship between inundation and NDVI (a spectrally derived indicator of plant productivity) in a 0.48-km² bald cypress stand in Sky Lake, an oxbow lake of the Yazoo River basin (Mississippi). We calculated NDVI from 63 cloud-free Landsat-5 scenes for 2003-2011. Inundation was estimated from daily pressure-transducer measurements of water depth at a reference location in the lake, and from surface topography of the stand estimated from Lidar data collected in February 2009 when no leaves were present on the trees and the entire vegetated area was free of standing water. After accounting for seasonal variation in NDVI associated with seasonal changes in cypress foliage, we found that NDVI integrated over the calendar year was inversely related to integrated water depths for the water year, meaning that an 18% variation in NDVI (from 0.34 to 0.28) was associated with variation in average inundation from 0.4 to 1.8 m. Within individual Landsat scenes, NDVI varied inversely with water depth as it did when integrated across the 9-year period of record. Although variation in NDVI associated with inundation is small compared to the variation associated with major disturbances such as hurricanes and fires, remotely estimated NDVI may more efficiently identify variation in bald cypress growth associated with variation in inundation, a result that would otherwise have to be confirmed by tree core analyses.