Review and Comparison

Dr. Gifford is Chairman of the Watershed Science Unit, College of Natural Resources, Utah State University, Logan, Utah 84322. He has conducted infiltration investigations into a big sagebrush (Artemesia tridentata) site in southern Idaho over a 12-year period. The site was plowed and seeded in the fall of 1968. Plowing apparently caused an initial significant decline in infiltration rates. Grazing, which began in 1970, did not further reduce infiltration but seasonal trends were eliminated and there was no recovery of infiltration. Exclosures which were built on-site indicate that, in this instance, it would take at least six years for complete recovery of infiltration rates, assuming no grazing. Dr. Gifford's report is interesting and informative and should be helpful in predicting hydrologic response to certain rangeland use practices. It is particularly interesting to me to compare Gifford's results to those which several of my graduate students and I have found in the sagebrush country of eastern Oregon. Among other things, we have attempted to determine hydrologic potential as based upon the subspecies of Artemesia tridentata. We have found that differences do exist, but that they are variable with site and location. A tendency toward increased hydrologic hazard (lower infiltration rates and increased potential sediment production) exists on the At. wyomingensis sites with a slight reduction of hazard in the At. trident ata and A.t. vaseyana sites. Our conclusion is that subspecies identification is not adequate, by itself, to identify hydrologic hazard; other factors including soil structure(particularly platyness and vesicular porosity), organic matter, and existing vegetation must be considered if one wishes to make predictions. We, like Gifford, have noted an initial decline in infiltration rates following land treatment. Seemingly, this decline is