Browsing by Author "Winter, Stephen L."

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Inconsistent outcomes of heterogeneity-based management underscore importance of matching evaluation to conservation objectives
(2013-08) McGranahan, Devan A.; Engle, David M.; Fuhlendorf, Samuel D.; Winter, Stephen L.; Miller, James R.; Debinski, Diane M.
Conservation policy often incentivizes managers of human-impacted areas to create landscape heterogeneity to maximize biodiversity. In rangeland, patchy disturbance regimes create landscape heterogeneity (patch contrast), but outcomes of heterogeneity-based management are rarely tested for a universal response. We analyzed four habitat variables – vegetation structure, plant functional group composition, litter cover, and bare ground – from five experimental rangelands in Oklahoma and Iowa, USA. We tested for response consistency to heterogeneity-based management across and within locations. We calculated effect sizes for each variable to compare patch contrast on pastures managed for heterogeneity (patch burn-grazing) and pastures managed for homogeneity (grazing with homogeneous fire regimes). Effects varied considerably across and within locations. Effects of heterogeneity-based management were positive for all variables at only three of five experimental rangeland locations. No location showed a consistent pattern of positive effect across all four variables, although one location showed no effect for any variable. At another location, we found a positive effect of heterogeneity-based management on litter cover and bare ground, but no effect on vegetation structure and plant functional group composition. We discuss effect variability and how the fire–grazing interaction applies to rangeland management and conservation. Although it is accepted practice to use heterogeneity-based management to increase rangeland habitat diversity, managers should also confirm that evaluation metrics match desired conservation outcomes.
Temporal variability in aboveground plant biomass decreases as spatial variability increases
(2016-03) McGranahan, Devan A.; Hovick, Torre J.; Elmore, R. Dwayne; Engle, David M.; Fuhlendorf, Samuel D.; Winter, Stephen L.; Miller, James R.; Debinski, Diane M.
Ecological theory predicts that diversity decreases variability in ecosystem function. We predict that, at the landscape scale, spatial variability created by a mosaic of contrasting patches that differ in time since disturbance will decrease temporal variability in aboveground plant biomass. Using data from a multi-year study of seven grazed tallgrass prairie landscapes, each experimentally managed for one to eight patches, we show that increased spatial variability driven by spatially patchy fire and herbivory reduces temporal variability in aboveground plant biomass. This pattern is associated with statistical evidence for the portfolio effect and a positive relationship between temporal variability and functional group synchrony as predicted by metacommunity variability theory. As disturbance from fire and grazing interact to create a shifting mosaic of spatially heterogeneous patches within a landscape, temporal variability in aboveground plant biomass can be dampened. These results suggest that spatially heterogeneous disturbance regimes contribute to a portfolio of ecosystem functions provided by biodiversity, including wildlife habitat, fuel, and forage. We discuss how spatial patterns of disturbance drive variability within and among patches.