Spatial Heterogeneity Across Five Rangelands Managed with Pyric-Herbivory

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McGranahan, Devan
Engle, David
Fuhlendorf, Samuel
Winter, Steven
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Debinski, Diane
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Ecology, Evolution and Organismal Biology

The Department of Ecology, Evolution, and Organismal Biology seeks to teach the studies of ecology (organisms and their environment), evolutionary theory (the origin and interrelationships of organisms), and organismal biology (the structure, function, and biodiversity of organisms). In doing this, it offers several majors which are codirected with other departments, including biology, genetics, and environmental sciences.

The Department of Ecology, Evolution, and Organismal Biology was founded in 2003 as a merger of the Department of Botany, the Department of Microbiology, and the Department of Zoology and Genetics.

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1. Many rangelands evolved under an interactive disturbance regime in which grazers respond to the spatial pattern of fire and create a patchy, heterogeneous landscape. Spatially heterogeneous fire and grazing create heterogeneity in vegetation structure at the landscape level (patch contrast) and increase rangeland biodiversity. We analysed five experiments comparing spatially heterogeneous fire treatments to spatially homogeneous fire treatments on grazed rangeland along a precipitation gradient in the North American Great Plains. 2. We predicted that, across the precipitation gradient, management for heterogeneity increases both patch contrast and variance in the composition of plant functional groups. Furthermore, we predicted that patch contrast is positively correlated with variance in plant functional group composition. Because fire spread is important to the fire–grazing interaction, we discuss factors that reduce fire spread and reduce patch contrast despite management for heterogeneity. 3. We compared patch contrast across pastures managed for heterogeneity and pastures managed for homogeneity with a linear mixed effect (LME) regression model. We used the LME model to partition variation in vegetation structure to each sampled scale so that a higher proportion of variation at the patch scale among pastures managed for heterogeneity indicates patch contrast. To examine the relationship between vegetation structure and plant community composition, we used constrained ordination to measure variation in functional group composition along the vegetation structure gradient. We used the meta-analytical statistic, Cohen’s d, to compare effect sizes for patch contrast and plant functional group composition. 4. Management for heterogeneity increased patch contrast and increased the range of plant functional group composition at three of the five experimental locations. 5. Plant functional group composition varied in proportion to the amount of spatial heterogeneity in vegetation structure on pastures managed for heterogeneity. 6.Synthesis and applications. Pyric-herbivory management for heterogeneity created patch contrast in vegetation across a broad range of precipitation and plant community types, provided that fire was the primary driver of grazer site selection. Management for heterogeneity did not universally create patch contrast. Stocking rate and invasive plant species are key regulators of heterogeneity, as they determine the influence of fire on the spatial pattern of fuel, vegetation structure and herbivore patch selection, and therefore also require careful management.


This is a manuscript of an article in Journal of Applied Ecology 49 (2012): 903, doi:10.1111/j.1365-2664.2012.02168.x. Posted with permisison.

Sun Jan 01 00:00:00 UTC 2012