Floodplain vegetation dynamics of Sipsey River, Alabama

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The Sipsey River creates Alabama’s one of the free-flowing freshwater floodplain forest and supports a high diversity of flora and fauna. This study evaluated the effects of local climate and inundation frequency on the floodplain dynamics for the period between 1990 and 2013, using a combination of remote sensing and GIS approaches. Normalized Difference Vegetation Index was used as a proxy of vegetation productivity. Vegetation types were identified by two methods- unsupervised classification and Seasonality Index. Three dominant vegetation types identified were-hardwood swamp, bottomland hardwoods and pinelands. Elevation and seasonality were found to play an important role in maintaining the distribution of the vegetation types. Change detection from 1990 to 2008 by both the methods identified a decrease in hardwood swamps and increase in bottomland hardwoods and pineland trees. Temporal variability in NDVI of two vegetation types, hardwood swamp and bottomland hardwoods, was explained by monthly average temperature as indicated by partial least square regression models. Spatial variability in the NDVI due to different flood magnitudes was assessed by using a 2D hydrodynamic model (Cellular Automaton Evolutionary Slope and River model). Results of linear regression showed no relationship between the flood inundation frequency and NDVI associated with the two vegetation types. The study presents baseline information about the overall floodplain vegetation dynamics of one of the few remaining unregulated rivers in Alabama. The need for higher spatial/ temporal resolution data and longer model simulation is recognized for more in-depth study.

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