The phytogeomorphology of the Niobrara region near Meadville, Nebraska.

One of the most phytogeomorphologically unique areas of Nebraska occurs along the Niobrara River Valley north of the community of Ainsworth. Not only is this an area where the Rocky Mountain, Eastern Deciduous and Northern Boreal Forest converge, but it is also an area of relatively recent geomorphic activity. Landslides are known to have occurred here; there is evidence of very recent, active movement as well as older, stabilized landslides. The purpose of this study was to examine the relationship between plant communities and geomorphic history. Three 100 m long transects were surveyed in each of the five study areas, all but two having different geomorphic histories. Mature tree, those with a diameter at breast height (DBH) of greater than two centimeters were derived from a statistical analysis of the importance values. Slopes that have not undergone movement display a specific distribution of mature trees: mesic species, such as green ash and linden, on footslopes, an oak-juniper association on midslopes and Ponderosa pine on ridgetops. The distribution is shifted downward in elevation on those slopes that have experience recent land slippages. Landslides also alter the topography of the valley, allowing species normallu found at one particular elevation to become established at another elevation. For example, pine trees can be found along the stream bank, and cotton woods on midslopes. As the landslide area ages, vegetation appears to succeed back to the typical distribution, that is a community adapted to a particular elevation on an undisturbed slope