Should Heterogeneity Be the Basis for Conservation? Grassland Bird Response to Fire and Grazing

Abstract

In tallgrass prairie, disturbances such as grazing and fire can generate patchiness across the landscape, contributing to a shifting mosaic that presumably enhances biodiversity. Grassland birds evolved within the context of this shifting mosaic, with some species restricted to one or two patch types created under spatially and temporally distinct disturbance regimes. Thus, management-driven reductions in heterogeneity may be partly responsible for declines in numbers of grassland birds. We experimentally altered spatial heterogeneity of vegetation structure within a tallgrass prairie by varying the spatial and temporal extent of fire and by allowing grazing animals to move freely among burned and unburned patches (patch treatment). We contrasted this disturbance regime with traditional agricultural management of the region that promotes homogeneity (traditional treatment). We monitored grassland bird abundance during the breeding seasons of 2001-2003 to determine the influence of altered spatial heterogeneity on the grassland bird community. Focal disturbances of patch burning and grazing that shifted through the landscape over several years resulted in a more heterogeneous pattern of vegetation than uniform application of fire and grazing. Greater spatial heterogeneity in vegetation provided greater variability in the grassland bird community. Some bird species occurred in greatest abundance within focally disturbed patches, while others occurred in relatively undisturbed patches in our patch treatment. Henslow's Sparrow, a declining species, occurred only within the patch treatment. Upland Sandpiper and some other species were more abundant on recently disturbed patches within the same treatment. The patch burn treatment created the entire gradient of vegetation structure required to maintain a suite of grassland bird species that differ in habitat preferences. Our study demonstrated that increasing spatial and temporal heterogeneity of disturbance in grasslands increases variability in vegetation structure that results in greater variability at higher trophic levels. Thus, management that creates a shifting mosaic using spatially and temporally discrete disturbances in grasslands can be a useful tool in conservation. In the case of North American tallgrass prairie, discrete fires that capitalize on preferential grazing behavior of large ungulates promote a shifting mosaic of habitat types that maintain biodiversity and agricultural productivity.

Macroinvertebrate Community Structure in Three‐Gorges Reservoir, China

“…In addition, the TWINSPAN classification results were applied as the second matrix in Detrended Correspondence Analysis (DCA). DCA was used to explore gradients in the benthic macroinvertebrate composition and elucidate compositional changes over time (FUHLENDORF et al, 2006). In order to evaluate how well the distances in the ordination space represent the distances in the original, unreduced space, the after-the-fact evaluation with relative Euclidean distance was performed (WALD- HARDT and OTTE, 2003).…”

Landscapes as a moderator of thermal extremes: a case study from an imperiled grouse

“…Bison and cattle units are stocked with similar, moderate stocking rates (bison: 2.1 AUM/ha; cattle: 2.4 AUM/ha). Vegetation structure and composition at the preserve are driven by the interacting effects of fire and grazing and the corresponding out-ofphase succession from these disturbances (Fuhlendorf et al 2006, Allred et al 2011. For more detailed information on the management at the Tallgrass Prairie Preserve refer to Hamilton (2007).…”

Structural heterogeneity increases diversity of non‐breeding grassland birds

“…This approach has been termed ''management toward the middle'' and reflects the intermediate disturbance model that has shaped rangeland management, but has failed to recognize the diverse needs of grassland organisms and the historically diverse structure of grasslands posited to have occurred pre-European settlement (Fuhlendorf and Engle 2001, Powell 2006. Management aimed at uniform disturbance limits the amount of undisturbed patches across the landscape necessary for certain species life history traits and fulfills the habitat requirements of a limited suite of generalized bird species (Reinking 2005, Fuhlendorf et al 2006, Powell 2008. The separation of the fire-grazing interaction can simplify rangeland communities and limit ecosystem structure and function Engle 2001, Hoekstra et al 2005).…”

“…While there is evidence that burning and grazing can act independently to influence grassland plant communities this typically does not result in structural heterogeneity that drives diversity in grassland bird communities (Valone and Kelt 1999, Davis 2004, Coppedge et al 2008. Diverse communities of species require habitat heterogeneity that includes intensively disturbed habitats (i.e., bare ground and relatively shortstatured vegetation) and habitats with minimal disturbance dispersed as a shifting mosaic across a complex landscape (Knopf 1994, Fuhlendorf et al 2006, Fuhlendorf et al 2009). Furthermore, the response of wildlife to disturbance processes, particularly birds, can vary greatly based on the duration and seasonal timing of disturbances (Brawn et al 2001, Gregory et al 2010.…”