Fire and flood expand the floodplain shifting habitat mosaic concept

Abstract

The floodplain shifting habitat mosaic concept suggests that habitat patch dynamics are influenced by hydrologic disturbances driven by flood pulses of sufficient power to initiate incipient motion of the substratum and maintain cut-and-fill alluviation of the channel and banks. However, floodplain habitat mosaics are subject to other important landscape-scale disturbance regimes. In the Rocky Mountains of the USA and Canada, fire also affects floodplain habitat patch composition. The floodplain exists at the intersection of disturbance regimes that shape the riverscape and those that shape the landscape. We extended the shifting habitat mosaic concept by examining the effects of multiple disturbance elements on habitat patch composition across the aquatic–terrestrial ecotone of the North Fork of the Flathead River, a free-flowing river in southeastern British Columbia, Canada, and northwestern Montana, USA. We used remotely sensed imagery, meteorological records, empirical and modeled rainfall-runoff data, extent and frequency of past wildfires, and anthropogenic landuse data for 1991–2013 to examine the relationships among hydrology, fire, landuse, geomorphic position, and floodplain habitat patch dynamics. Exploratory path analysis revealed that fire had the strongest total effect and stream power and geomorphic position had moderate total effects on the variability of floodplain habitat patch composition along the North Fork. These 3 factors explained 13 to 26% of the variance in floodplain habitat patch composition between study reaches across all years. We used graphical analysis to examine the locations and intensity of disturbance and recovery pathways across floodplain transition zones throughout the study period. Our results support the hypothesis that hydrologic and fire disturbances and recovery pathways maintain the shifting habitat mosaic across the floodplains of this river system.