Evaluating the invasion of red cedar (Juniperus viriginiana) downstream of Gavins Point Dam, Missouri National Recreational River

Background/Question/Methods

Gavins Point Dam, the final dam on the main-stem Missouri River, alters downstream river form and function.  Throughout a 59-mile downstream reach, the dam reduces overbank flooding and lowers the water surface by 1-3 meters.  Under the dam-created hydro-geomorphic conditions, native cottonwood trees are unable to regenerate.  The limited regeneration of native riparian cottonwoods, the lowered water surface, and the reduced overbank flooding creates a terrace environment within the riparian habitat.  Consequently, red cedars, a native upland tree, are invading this new terrace-like riparian environment.  To this end, we apply Bayesian statistical models to investigate patterns of red cedar riparian invasion and assess ecosystem function patterns along this flow-regulated reach. We set-up plots within cottonwood stands along a 59-km downstream reach of Gavins Point Dam.  Within each plot, we collected soil samples, litter samples, stem densities of trees, and collected cores of the largest cottonwood and red cedar in each plot.  In the regression model, we input soil texture data and tree composition and structure data.  To assess influences of red cedar on soil indicators of ecosystem function and general patterns of ecosystem function within the study area, we measured organic carbon, nitrogen, pH, electrical conductivity, and hydrophobicity.

Results/Conclusions

Red cedars existed along the floodplain prior to regulation.  However, according to our tree age data and stem density data red cedars existed at a lower population than today.  We found that 2 out of 565 red cedars established before the dam was completed. Also, we found no significant difference in soil properties between soils with established red cedar and soils with established cottonwood. By studying soil texture data, and interpreting fluvial geomorphic surfaces in the field and via aerial photography, we found soil texture generally reflects the type of fluvial surface created before or at the beginning of flow regulation.  Red cedar establishment and soil property differences are correlated to percent sand in the soil. According to our interpretation of geomorphic surfaces, the sandier soils represent higher energy depositional surfaces, such as islands and pointbars.  Thus, these legacy geomorphic surfaces are a determinant of red cedar establishment patterns and soil property patterns.  Land managers and other researchers needing to make predictions for other areas can use our model-building process to quickly map and assess impacts of invasion.  The Bayesian model provides information about feedbacks between environmental parameters that can help determine and target restoration goals.