Spatial heterogeneity across five rangelands managed with pyric-herbivory

article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. 2 24 Summary 25 1. Many rangelands evolved under an interactive disturbance regime in which grazers 26 respond to the spatial pattern of fire and create a patchy, heterogeneous landscape. 27 Spatially heterogeneous fire and grazing create heterogeneity in vegetation structure at 28 the landscape level (patch contrast) and increase rangeland biodiversity. We analysed five 29 experiments comparing spatially heterogeneous fire treatments to spatially homogeneous 30 fire treatments on grazed rangeland along a precipitation gradient in the North American 31 Great Plains. 32 2. We predicted that, across the precipitation gradient, management for heterogeneity 33 increases both patch contrast and variance in the composition of plant functional groups. 34 Furthermore, we predicted that patch contrast is positively correlated with variance in 35 plant functional group composition. Because fire spread is important to the fire–grazing 36 interaction, we discuss factors that reduce fire spread and reduce patch contrast despite 37 management for heterogeneity. 38 3. We compared patch contrast across pastures managed for heterogeneity and pastures 39 managed for homogeneity with a linear mixed-effect (LME) regression model. We used 40 the LME model to partition variation in vegetation structure to each sampled scale so that 41 a higher proportion of variation at the patch scale among pastures managed for 42 heterogeneity indicates patch contrast. To examine the relationship between vegetation 43 structure and plant community composition, we used constrained ordination to measure 44 variation in functional group composition along the vegetation structure gradient. We 45 3 used the meta-analytical statistic, Cohen's d, to compare effect sizes for patch contrast 46 and plant functional group composition. 47 4. Management for heterogeneity increased patch contrast and increased the range of plant 48 functional group composition at three of the five experimental locations. 49 5. Plant functional group composition varied in proportion to the amount of spatial 50 heterogeneity in vegetation structure on pastures managed for heterogeneity. 51 6. Synthesis and applications. Pyric-herbivory management for heterogeneity created patch 52 contrast in vegetation across a broad range of precipitation and plant community types, 53 provided that fire was the primary driver of grazer site selection. Management for 54 heterogeneity did not universally create patch contrast. Stocking rate and invasive plant 55 species are key regulators of heterogeneity, as they determine the influence of fire on the 56 spatial pattern …