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

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 guided by historical disturbance patterns, on vegetation structure and bird abundance in shortgrass steppe 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; control pastures were not burned. Patch-burn grazing management increased vegetation heterogeneity by generating short (<4 cm), 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 6 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, whereas 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. Consistent with this pattern, patch-burn grazing management reduced the abundance of all 3 species at the whole-pasture scale. We found no evidence that unburned patches within the patch-burned pastures 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. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Disturbance shapes avian communities on a grassland–sagebrush ecotone

“…In an ecotone between the sagebrush steppe and the Great Plains, bird communities responded strongly to fire and burrowing mammals, lending further support for the critical role of disturbance regimes in driving biodiversity in North American rangelands (Kotliar et al 1999, Fuhlendorf et al 2006, Augustine and Derner 2015. For example, without black-tailed prairie dogs, the imperiled mountain plover would be rare in or entirely absent from our study area (see also Dinsmore et al 2005).…”

“…In some parts of this region, disturbances were frequent, intense, and interactive, creating shifting vegetation mosaics that supported diverse habitats and led to increased biodiversity at broad scales Engle 2001, Skagen et al 2018). Further, vegetation heterogeneity engendered by patchy disturbance has been linked to higher bird diversity in tallgrass, mixed-grass, and shortgrass prairies (Coppedge et al 2008, Augustine and Baker 2013, Augustine and Derner 2015. Further, vegetation heterogeneity engendered by patchy disturbance has been linked to higher bird diversity in tallgrass, mixed-grass, and shortgrass prairies (Coppedge et al 2008, Augustine and Baker 2013, Augustine and Derner 2015.…”

“…North American grassland birds evolved in the context of these frequent disturbances (Brawn et al 2001), and some species benefit specifically from fire as well as biotic ecosystem engineering via grazing by large ungulates or burrowing and clipping action by prairie dogs (Johnson 1997, Grant et al 2010, Augustine and Derner 2012, Ahlering and Merkord 2016. Further, vegetation heterogeneity engendered by patchy disturbance has been linked to higher bird diversity in tallgrass, mixed-grass, and shortgrass prairies (Coppedge et al 2008, Augustine and Baker 2013, Augustine and Derner 2015.…”

Extremes of heat, drought and precipitation depress reproductive performance in shortgrass prairie passerines

“…See Skagen et al . (), Skagen and Yackel Adams (), and Augustine and Derner () for further details of vegetation sampling methodology.…”

“…Within study plots, we estimated per cent cover of vegetation types and measured grass height (cm) in six or 12 5-m-radius plots or within 36 or 45 20-cm 9 50-cm Daubenmire frames (Daubenmire 1959). See Skagen et al (2005), Skagen and Yackel Adams (2012), and Augustine and Derner (2015) for further details of vegetation sampling methodology.…”