Inconsistent outcomes of heterogeneity-based management underscore importance of matching evaluation to conservation objectives

Abstract

Winter, Stephen L.; Miller, James R.; and Debinski, Diane M., "Inconsistent outcomes of heterogeneity-based management underscore importance of matching evaluation to conservation objectives" (2013 AbstractConservation 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

“…Asynchronous patch‐level succession explains the diversity observed in spatially heterogeneous landscapes, as a breadth of organisms find specific resources not otherwise available in space or time in spatially homogenous landscapes (reviewed in McGranahan et al. ), but offers little to understand how patch‐specific dynamics vary across space and through time and thus contribute to landscape‐level functionality. Metacommunity theory, however, allows patches to be considered at two spatial scales simultaneously, as spatially discrete communities with independent processes that collectively contribute to landscape‐level ecological properties (Loreau ).…”

“…Simply stated, heterogeneous landscapes, which include lawn‐like patches to deep litter and tall, rank necromass, support greater biological diversity than homogeneous landscapes (McGranahan et al. ). And in periods of drought and/or high animal numbers, previously ungrazed, accumulated biomass functions as emergency forage for herbivores (Fynn ).…”

Moderate patchiness optimizes heterogeneity, stability, and beta diversity in mesic grassland

“…Beta diversity was the original spatial component of diversity, and has since been extended to represent compositional dissimilarity as a groups’ breadth or range in the multivariate space of an ordination, a conventional community analysis (Anderson, Ellingsen, & McArdle, ). Given that patch contrast in heterogeneous rangeland is characterized by dissimilarity in plant functional group composition (Fuhlendorf et al., ; McGranahan et al., ), using multivariate dispersion—the range of spread in ordination space—as a measure of beta diversity might also correlate with spatial heterogeneity (Anderson et al., ). Together, describing spatial heterogeneity and temporal variability in terms of contrast among patches for productivity and structure, and beta diversity for composition, might present a useful framework for managers to assess heterogeneity‐based management.…”

Temporal variability in aboveground plant biomass decreases as spatial variability increases

“…Aboveground biomass relates to a breadth of functions, including wildlife habitat, fuel for fire, and forage for herbivores. Simply stated, heterogeneous landscapes, which include lawnlike patches to deep litter and tall, rank necromass, support greater biological diversity than homogeneous landscapes (McGranahan et al 2013). And in periods of drought and/or high animal numbers, previously ungrazed, accumulated biomass functions as emergency forage for herbivores (Fynn 2012).…”

“…Previously the shifting landscape mosaic created by patches with different times since fire has been described as being driven by the same processes of ecological disturbance and secondary succession that are asynchronous across patches (Fuhlendorf and Engle 2004). Asynchronous patch-level succession explains the diversity observed in spatially heterogeneous landscapes, as a breadth of organisms find specific resources not otherwise available in space or time in spatially homogenous landscapes (reviewed in McGranahan et al 2013), but offers little to understand how patch-specific dynamics vary across space and through time and thus contribute to landscape-level functionality. Metacommunity theory, however, allows patches to be considered at two spatial scales simultaneously, as spatially discrete communities with independent processes that collectively contribute to landscape-level ecological properties (Loreau 2009) .…”