Flow modification by dams can have significant effects on patch dynamics and riparian tree demography in downstream riparian ecosystems. In western North America, a number of studies have demonstrated the sensitivity of riparian Populus species (cottonwoods) to the effects of flow regulation. The focus of our research is to quantify and contrast pre- and post-dam landscape dynamics, land cover, plant species composition, and cottonwood forest age distribution along several segments of the regulated Missouri River.
Results/Conclusions
GIS analysis of historic maps and aerial photography on a 95 km unchannelized segment of the Missouri show a dramatic shift from 1892 to 2006 in the dominant land cover from grassland to row crops, a 50% decline in forest area and fragmentation of remaining forest patches, and a decline in the area of sandbars. The present-day forest has nearly equal areas composed of stands originating pre- (>50 years old) and post-dam (<50 years old), with most of the forest either 25-50 years old (34%) or 51-114 years old (40%). Areas <25 years old compose only 16% of the total forest area, suggesting that recruitment limitation has occurred during recent decades. We hypothesize that the relatively large area of forest that established in the two decades after dam closure was a legacy of the flood of record on the river in 1952, followed by the subsequent stabilization of flows due to dam closure in the mid-1950s. Future analyses will compare different Missouri River segments to determine if differences in geomorphic context among river segments influence patterns of pre- and post-dam landscape dynamics and forest age structure.