Forest Response to High Duration and Intensity Flooding along Pool 26 of the Upper Mississippi River

摘要

Many natural resource managers could not anticipate the effects that the flood of 1993 would have on floodplain forests of the Upper Mississippi River. Previous experience suggested that floodplain forests were adapted to such events and should only experience removal of upland a non-native species. However, when trees considered highly flood tolerant did not leaf out in the spring of 1994, natural resource managers began to realize the serious impact that a large-scale flood could have on floodplain forest communities. To better understand these impacts, researchers with the Long Term Resource Monitoring Program at Pool 26 of the Upper Mississippi River System (UMRS) began describing forest community response to the large-scale flood of 1993. The floodplain forests of the UMRS are some of the most productive ecosystems worldwide. These communities provide habitat and forage for many species of wildlife, produce timber, and provide a valuable carbon dioxide sink. Like many other plant communities, floodplain forest successional patterns are largely driven by disturbance events (e.g., fire, wind-throw, flooding, drought, and physical erosion/deposition). Black willow and eastern cottonwood regenerate on recent deposits of substrate (mainly sand) created by the river. As a result of annual floods, fine sediment drops out of suspension and the low landform occupied by the willow/cottonwood community develops into a low terrace. At the same time, the willow/cottonwood community is gradually being replaced by silver maple and green ash. The process of terrace building continues and communities of mixed forests and oak forests develop as elevation increases and the frequency of flooding decreases. Understanding how these communities respond to the various disturbance events, particularly large scale flooding, is important to natural resource managers who are trying to manage for specific or diverse floodplain forest.