Flood Plain Vegetation Changes on the Grant-Kohrs Ranch National Historic Site Between 1993 and 2000

Bedunah, Don; Jones, Thad

We evaluated the report "Vegetation Mapping and Analysis of the Grant-Kohrs National Historic Site" by Thompson et al. (1995) and determined vegetation and riparian health changes between 1993 and 2000 on riparian sites on the Grant-Kohrs Ranch National Historic Site. We found the methodology and procedures of Thompson et al. (1995) to be accepted procedures for a mapping of riparian plant communities and determination of riparian health for management studies. We then repeated their measurements to determine if their measurements were accurate and to determine changes between 1993 and 2000. We located 13 riparian polygons where fences excluded livestock grazing and other known disturbances (i.e., such as fire) had not occurred and thus allowed for direct comparisons between study periods. We found few differences in species composition and no difference in structural diversity or plant communities between 1993 and 2000. We believe the relatively few changes in species composition, and no changes in area of plant communities between 1993 and 2000, suggests that plant community recovery is being delayed by non-livestock grazing factors. Polygon health measurements did show improvement between 1993 and 2000. The improvement in polygon health was associated with decreased shrub utilization, decreased standing decadent and dead woody material, shrub regeneration, increased deep binding rootmass, and increased streambank stability. However, the very dry conditions of 2000, and the resulting low stream flows, produced seasonal improvement (i.e., streambanks appeared more stable), but may not be representative of bank erosion dynamics during a more normal or average stream-flow period. We hypothesize that the factor or factors delaying recovery are related to site changes, but the riparian health evaluation methods used by Thompson et al. (1995) and repeated for this study are too coarse for assigning levels of site specific causative factors.