Present and historic riparian vegetation among ecoregions of the White River, an unregulated Great Plains river

Background/Question/Methods

The White River runs from northwestern Nebraska, through southwestern South Dakota until it enters the Missouri River at Lake Francis Case.  At 816 km (508 miles), the White is one of the longest undammed rivers in the lower 48 states. It flows through three major (Level IV) ecoregions (Semiarid Pierre Shale Plains, White River Badlands, and River Breaks) and a short section influenced by reservoir levels at Lake Francis Case (delta).  The purpose of this study is to examine composition and variation of the plant communities among the three ecoregions and delta.  The results of this study will enhance the understanding of unregulated Great Plains rivers across temporal and spatial scales.  The land cover of the entire riparian corridor was mapped using GIS with 2010 NAIP imagery and was compared among ecoregions.  Selected reaches were mapped using historical aerial images from the last 75 years in order to assess and quantify temporal changes to communities and channel dynamics.  Vegetation was surveyed in all major community types throughout the river’s riparian zone to quantify the composition and structural differences among ecoregions. 

Results/Conclusions

GIS analysis of 2010 land cover showed the proportion of the riparian corridor composed of forest varied from 11% in the White River Badlands up to 41% in the delta, with Semiarid Pierre Shale Plains and River Breaks forests composing 20% and 24% of the riparian corridor, respectively.  Pierre Shale woodlands were dominated by Acer negundo (70%) and Populus deltoides (24%).  The Badlands woodlands were dominated by Fraxinus. pennsylvanica (51%) and P. deltoides (26%) with a higher relative shrub species density than the other ecoregions (18%).  River Breaks woodlands were dominated by F. pennsylvanica (52%) and Salix eriocephala (25%) with P. deltoides relative density at 5%.  The delta woodlands were dominated by F. pennsylvanica (35%), P. deltoides (24%), Salix exigua (22%), and S. amygdaloides (14%).  In each of the ecoregions the percent basal area of P. deltoides was greater than its relative density, implying forests aging in succession.  Woody species richness increased along ecoregions from Pierre Shale to River Breaks, decreasing in the delta.  These data show that the dominant woody species, relative basal area, and richness of the White River riparian forests vary among the different ecoregions, suggesting the importance of coarse scale controls on riparian communities.