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Submitted to: The Wildlife Society
Publication Type: Abstract Only Publication Acceptance Date: 6/22/2010 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Combining prescribed fire and grazing management has been recommended as a tool to generate a heterogeneous vegetation mosaic for grassland birds. Past studies addressing this interaction of fire and grazing have primarily focused on tallgrass prairies of the eastern Great Plains, while less is known about fire-grazing interactions in semi-arid grasslands of the western Great Plains. We initiated a patch burning experiment in shortgrass steppe (northeastern Colorado) comparing 3 unburned pastures with 3 pastures in which 25% of the area is burned each year. Burns were implemented in November of 2007 and 2008, and vegetation, cattle, pronghorn (Antilocapra americana) and grassland bird responses monitored during the 2008 and 2009 growing seasons. Herbaceous plant production on burns (mean + 1SE = 498 + 82 kg ha-1) was similar to unburned sites (462 + 53 ka ha-1; P = 0.73) during the first post-burn growing season. Burns influenced vegetation structure by removing >95% of standing dead biomass, and reducing vertical vegetation density in mid-June by 53% (1.8 + 0.2 cm on burns vs. 3.8 + 0.3 cm in unburned sites). Cattle preferentially grazed on burns in August (P = 0.067) when forage was green but not in June (P=0.33) when forage was senescent due to low precipitation. Patch burning did not influence cattle weights gains (1.07 kg/steer/day in patch burned pastures vs. 1.06 kg/steer/day in control pastures). Pronghorn densities during March - September were 2.7 times greater on burns compared to adjacent unburned portions of pastures. Grassland birds showed strong responses to the heterogeneous vegetation mosaic produced by patch burn grazing management. When analyzed at a 16-ha spatial resolution (i.e. the size of the patch burns), horned lark (Eremophila alpestris) abundance was significantly negatively correlated with vegetation visual obstruction readings (VOR) in both years (r2 = 0.55 and 0.25 respectively). We positively correlated with VOR in a wet year (r2 = 0.63), and were less common and only found on unburned sites with high VOR in a dry year. Mountain plovers (Charadrius montanus) only occurred on current-year burns in both years. Findings suggest that patch burn grazing management can be an effective tool to manage habitat for sustaining grassland bird diversity in the western Great Plains. |
