title: Climate, hydrologic disturbance, and succession: drivers of floodplain pattern.
abstract: Floodplains are among the world's most threatened ecosystems due to the pervasiveness of dams, levee systems, and other modifications to rivers. Few unaltered floodplains remain where we may examine their dynamics over decadal time scales. Our study provides a detailed examination of landscape change over a 60-year period (1945-2004) on the Nyack floodplain of the Middle Fork of the Flathead River, a free-flowing, gravel-bed river in northwest Montana, USA. We used historical aerial photographs and airborne and satellite imagery to delineate habitats (i.e., mature forest, regenerative forest, water, cobble) within the floodplain. We related changes in the distribution and size of these habitats to hydrologic disturbance and regional climate. Results show a relationship between changes in floodplain habitats and annual flood magnitude, as well as between hydrology and the cooling and warming phases of the Pacific Decadal Oscillation (PDO). Large magnitude floods and greater frequency of moderate floods were associated with the cooling phases of the PDO, resulting in a floodplain environment dominated by extensive restructuring and regeneration of floodplain habitats. Conversely, warming phases of the PDO corresponded with decreases in magnitude, duration, and frequency of critical flows, creating a floodplain environment dominated by late successional vegetation and low levels of physical restructuring. Over the 60-year time series, habitat change was widespread throughout the floodplain, though the relative abundances of the habitats did not change greatly. We conclude that the long- and short-term interactions of climate, floods, and plant succession produce a shifting habitat mosaic that is a fundamental attribute of natural floodplain ecosystems.
authors.affiliation: Flathead Lake Biological Station, Division of Biological Sciences, The University of Montana, 311 Bio Station Lane, Polson, Montana 59860-9659, USA. diane.whited@umontana.edu
authors.forename: Diane C
authors.initials: DC
authors.lastname: Whited
authors.forename: Mark S
authors.initials: MS
authors.lastname: Lorang
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Harner
authors.forename: F Richard
authors.initials: FR
authors.lastname: Hauer
authors.forename: John S
authors.initials: JS
authors.lastname: Kimball
authors.forename: Jack A
authors.initials: JA
authors.lastname: Stanford
mesh_terms: D002980:Climate; D003247:Conservation of Natural Resources; D017753:Ecosystem; D004777:Environment; D009009:Montana; D063245:Plant Development; D011157:Population Dynamics; D045483:Rivers; D014197:Trees; D014872:Water Movements; D014881:Water Supply