Patch-burn grazing management, vegetation heterogeneity and avian responses in a semi-arid grassland

Authors: Augustine, David; Derner, Justin

Submitted to: Journal of Wildlife Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2015
Publication Date: 6/25/2015
Publication URL: https://handle.nal.usda.gov/10113/61637
Citation: Augustine, D.J., Derner, J.D. 2015. Patch-burn grazing management, vegetation heterogeneity and avian responses in a semi-arid grassland. Journal of Wildlife Management. DOI: 10.1002/jwmg.909.

Interpretive Summary: In grasslands of the North American Great Plains, differences between pre-European and current-day effects of grazing and fire on the vegetation may be changing habitats for grassland birds and contributing to declines in their populations. We examined the influence of patch-burn grazing management, which is a management strategy that uses interactions between fire and livestock grazing, on vegetation structure (height and density) and bird abundance in rangeland in of northeastern Colorado, USA. All study pastures were grazed by cattle at moderate stocking rates from May to October each year. In the patch-burn treatment, we burned 25% of each pasture in autumn (Oct or Nov) each year during 2007 – 2010, while control pastures were not burned. Patch-burn grazing management created short, sparse vegetation on recent burns. Although cattle selectively grazed recent burns, this did not change the height or density of vegetation in unburned portions of patch-burned pastures relative to controls. Of the six grassland bird species we examined, mountain plovers occurred exclusively on recent burns whereas grasshopper sparrows occurred exclusively in grassland not burned for > 3 years. Two species (lark bunting and western meadowlark) were 2 – 3 times less abundant on recent burns compared to controls, while densities of horned larks and McCown’s longspur were unaffected by burning. Lark bunting, western meadowlark, and grasshopper sparrow densities changed substantially from year to year. In the years when they were abundant, all 3 species increased in density with increasing time since burning. Patch-burn grazing management was an effective strategy to create breeding habitat for mountain plovers. However, our findings suggest that in this type of rangeland, additional strategies that generate taller, more dense vegetation than occurs under moderate cattle grazing need to be considered in combination with patch-burn grazing management to sustain breeding habitat for the full suite of native grassland birds.

Technical Abstract: Anthropogenic changes to disturbance regimes in grasslands, and associated homogenization of vegetation structure, have been implicated as factors contributing to declines in populations of grassland birds in North America. We examined the influence of patch-burn grazing management, which employs spatiotemporal interactions between fire and livestock grazing, on vegetation structure and bird abundance in a semiarid grassland in northeastern Colorado, USA. All study pastures were grazed by cattle at moderate stocking rates from May to October each year. In the patch-burn treatment, we burned 25% of each pasture in autumn (Oct or Nov) each year during 2007 – 2010, while control pastures were not burned. Patch-burn grazing management increased vegetation heterogeneity by generating short, sparse vegetation on recent burns. Although cattle selectively grazed recent burns, this did not alter vegetation structure in unburned portions of patch-burned pastures relative to controls. Of the six grassland bird species we examined, mountain plovers (Charadrius montanus) occurred exclusively on recent burns whereas grasshopper sparrows (Ammodramus savannarum) occurred exclusively in grassland not burned for > 3 years. Two species (lark bunting [Calamospiza melanocorys] and western meadowlark [Sturnella neglecta]) were 2 – 3 times less abundant on recent burns compared to controls, while densities of horned larks (Eremophila alpestris) and McCown’s longspur (Rhynchophanes mccownii) were unaffected by burning. Lark bunting, western meadowlark, and grasshopper sparrow densities varied substantially among years. In the years when they were abundant, all 3 species increased in density across the time-since-burning gradient. We found no evidence that unburned patches within the patch-burn grazing treatment differed from unburned pastures in terms of the abundance of any bird species. Patch-burn grazing management was an effective strategy to create breeding habitat for mountain plovers. However, our findings suggest that in the shortgrass steppe, additional strategies that generate taller, more dense vegetation than occurs under moderate cattle grazing need to be considered in combination with patch-burn grazing management to sustain breeding habitat for the full suite of native grassland birds.