Ecohydrological response of tallgrass prairie rangelands to fire and grazing impacts from patch burning and annual burning regimes

Background/Question/Methods

Native grasslands are a unique ecosystem historically maintained by fire and grazing disturbance.  Patch burning is a management strategy used in native prairie rangelands to mimic historical grazing and fire interactions that has been shown to induce heterogeneity and native biodiversity within the landscape.  When a fire occurs on a portion of the landscape, the probability of grazing increases as animals graze the burned area heavily, allowing previously burned areas relief from heavy grazing pressure.  Both fire and grazing directly impact vegetation structure and land surface processes, which will influence the area’s hydrology, soil nutrient cycling and soil structure.  The objective of this study was to quantify the ecohydrological properties for two fire regimes: patches under different phases of recovery from fire on a 3-year burn rotation and annually burned prairie using the ongoing patch burning experiment at the Tallgrass Prairie Preserve in Oklahoma.  Bordered plots were installed in each patch of the patch burned unit and an annually burned pasture.  Rainfall was simulated at a 10-year intensity in April after a spring burn and in October after a complete growing and grazing season.   Ecological variables, runoff, sediment loss, infiltration rates and dissolved nutrients were determined under each treatment.

Results/Conclusions

Using a one-way ANOVA, preliminary results suggest that vegetation cover and biomass differed between treatments and between patches.  Total runoff volumes were significantly different between all treatments with the largest total runoff volume occurring on the recently burned patch that experienced a higher level of grazing activity than the annually burned treatment.  Sediment loads were significantly higher for the recently burned patch compared with the annually burned field even after a full growing season post-fire.  While both the patch burned and annually burned areas exhibited similar loads immediately after fire, the burned patch continued to have high levels of sediment loss even after a full growing season.  After two growing seasons, however, there was no significant difference between patch burning and annually burning treatments.  Our results suggest that while a combination of intense grazing pressure on recently burned patches reduced infiltration capacity and increased sediment loss, this effect is not retained into subsequent years and the burned patches recover after a year.  To further understand the impact grazing and fire patterns have on soil water retention and nutrient loss, comparisons of runoff and sediment loss over time need to be taken.