Seasonal bankfull flooding is a common disturbance in floodplain landscapes. Along with other processes, regular flooding generates shifts in the location of diverse aquatic and terrestrial floodplain habitat patches. Despite this spatial dynamism, the habitat types and their relative abundance remain relatively constant in the long-term. This phenomenon, known as the shifting habitat mosaic, is well established and is a critical process in riverine systems. However short-term patterns and processes that occur during seasonal flooding are less understood. It is possible that on the short timeframe of a bankfull flood disturbance, the floodplain landscape does not follow the shifting mosaic model and habitats destroyed in one location are not necessarily created in another. Understanding the link between changes in discharge and landscape patterns during a seasonal flood provides insight into the annual flux and spatial change in habitats, as well as the long-term structure and function of floodplains.
To improve understanding of floodplain habitat dynamics during disturbance, we collected aerial imagery of the Clark Fork River in western Montana on six dates in 2014 that spanned the seasonal flood. We georectified raw imagery to create nearly seamless digital images for each sample date. We used imagery from base flow conditions prior to the flood to identify three zones: the main channel, the parafluvial zone with recently scoured and deposited cobble and early stage vegetation present, and the orthofluvial zone with gallery forests, old channels, and herbaceous surfaces. We established permanent plots within these zones and the plot and zone boundaries were held constant throughout the flood pulse. We identified 17 different aquatic and terrestrial habitats from the photos using spectral signatures. We measured and mapped changes in the areal abundance of each habitat type within each floodplain zone from April through September. We tracked transitions in habitat type within each plot using alluvial diagrams to understand the development of individual habitat types during flood disturbance. Finally, we calculated two measures of habitat diversity (α and β) to understand how short-term floodplain complexity is impacted by seasonal flooding.
Driscoll, Katelyn P.; Hauer, F. Ric. 2019. Seasonal flooding affects habitat and landscape dynamics of a gravel-bed river floodplain. Freshwater Science 38(3):000-000.