Seasonal grazing affects soil physical properties of a montane riparian community

The effects of seasonal grazing treatments (early spring and late summer) on soil physical properties were studied in a montane riparian ecosystem in northern Colorado. Infiltration rates and bulk density were used as primary indicators of responses to a 1-time heavy grazing event on previously protected paddocks. Soil bulk density, porosity, gravimetric water content, organic carbon concentration and texture were measured at 0-5 cm, 5-10 cm, and 10-15 cm depths to determine how these parameters affected infiltration rates. Assessment of initial changes and subsequent recovery of the soil properties in response to the grazing treatments was conducted by measuring these parameters before each grazing event and at 4 time periods following the grazing event. Few differences between spring or late summer grazing periods on soil physical properties were found. A stepwise multiple regression model for infiltration rate based on soil physical properties yielded a low R-2 (0.31), which indicated much unexplained variability in infiltration. However, infiltration rates declined significantly and bulk density increased at the 5-10 cm depth and 10-15 cm depth in grazed plots immediately following grazing, but the highly organic surface layer (0-5 cm) had no significant compaction. Infiltration rates and soil bulk densities returned to pre-disturbed values within I year after grazing events, suggesting full hydrologic recovery. This recovery may be related to frequent freeze-thaw events and high organic matter in sons.