Ecohydrological response of native tallgrass prairie with fire and grazing disturbance

In prairie ecosystems, grazing and fire are interactive disturbances affecting soil infiltration capacity and erosion rates. Grasslands provide critical ecosystem services ranging from biodiversity conservation to water provisioning. To improve ecosystem services provided by these grasslands, a new management strategy called 'patch burn grazing', has been implemented within tallgrass and mixed grass prairies in Oklahoma, Texas, and Kansas. Under patch burn grazing, sections of a pasture are burned on rotation, focusing grazers onto specific areas within the landscape to mimic historic migratory grazing disturbance. The collective impact of fire followed by heaving grazing could reduce soil stability and increase nutrient transport into streams due to increased runoff. We used a rainfall simulator to simulate a rainfall event with a 10-year return storm intensity in a tallgrass prairie in northern Oklahoma within an annual burn grazing pasture (annual treatment) and a patch burn grazing pasture (patch treatment) to explore how pyric-herbivory could alter hydrological responses. Total runoff and sediment yield decreased exponentially as time since fire increased for both management approaches. Final infiltration rates were higher for the annual treatment than for the patch treatment at 6 months after fire (p<0.01). The patch treatment reached final infiltration rates similar to the annual treatment by 18 months since-fire (p = 0.761). Sediment yield in the burned patch was significantly higher than in the annual treatment 6-months since fire (p = 0.02). By the 18th month, sediment loads from the patch treatment had decreased to similar levels from the annual treatment. Water soluble K, P, NH4–N and NO 3-N were positively correlated with runoff rates and percent bare ground and negatively correlated with vegetative cover. All nutrients analyzed increased after fire and then decreased as time since fire increased. Our results suggest that a three year fire frequency provides sufficient time for heavily grazed patches in patch burn grazing management to reach higher infiltration rates and lower sediment yield than that in the annual burn grazing management.