Restoration enhances resistance of sagebrush-steppe communities following repeated fires but doesn’t reverse changes in ecosystem state

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Simon C. Power, G. Matt Davies, Jon D. Bakker

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Many ecosystems are currently subject to increased fire frequencies and invasive species introductions. Responses to these disruptions vary between ecosystems. For instance, those with species traits that support rapid regeneration post-fire may be unaffected by increased fire frequency. In contrast, ecosystems lacking such traits may respond by shifting to an alternative state. We investigated whether restoration efforts may reverse such shifts and increase resistance of sagebrush-steppe communities subjected to compounded wildfires and invasion by Bromus tectorum from 1992 to 2017. Community responses were assessed by analyzing changes in species abundances at multiple time points in 37 permanent plots in Washington, USA. The greatest change occurred in communities where the obligate seeding shrub Artemisia tridentata was common (> 25% cover). Repeated fires (up to 4) led to the extirpation of A. tridentata, which was initially replaced by native forbs/grasses and subsequently by B. tectorum. When restoration treatments (herbicide, seeding) were applied following fire, invasive species tended to show reduced dominance. Communities where resprouting grasses/shrubs were common showed the least change. Repeated fires did, however, lead to a gradual but substantial reduction (90% by 2017) in resprouting shrub abundances. Our findings suggest that communities with seeding shrubs that require extended fire intervals (< 30 years) to reestablish, lack resilience to increased fire frequency and are vulnerable to invasion. While restoration did enhance resistance in these communities, their shift to an alternative state suggests that they have evolved a degree of unhelpful resilience that requires sustained fire suppression and restorative interventions.

Resource Type:
Conference Presentation, SER2021

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