Productivity and Resilience: Long-Term Trends and Storm-Driven Fluctuations in the Plant Community of the Accreting Wax Lake Delta

River deltas are dynamic geologic features where the plant community engages in critical feedbacks with geomorphology, and plant community development is impacted by both riverine and coastal drivers. A vegetation index (NDVI) calculated from a time series of 54 peak growing season Landsat-5 TM and Landsat-7 ETM+ images was used to assess the long-term trends and storm event-driven changes in the vegetation community associated with the Wax Lake Delta, an actively accreting subdelta of the Mississippi River. Multiple regression models were developed to explain variation in the vegetated area of the delta and mean delta NDVI from 1984 to 2011 as a function of date, hydrology, and seasonality. The models indicate that both vegetated area and mean NDVI increased over time from 1984 to 2011. Productivity measures following Hurricanes Lili (2002), Rita (2005), and Ike (2008) represented statistical outliers; significant decreases in NDVI following these storms suggest that hurricanes passing directly over or to the west of the delta result in short-term disturbance to the plant community, most likely related to saltwater intrusion associated with storm surge. However, in each case, both vegetated area and mean NDVI recovered to the long-term trend by the following growing season. These results demonstrate that the freshwater marshes within this mineral-rich, accreting delta are increasing in productivity as the delta matures and are extremely resilient to coastal storm disturbance.