Extreme prescribed fire during drought reduces survival and density of woody resprouters

Abstract

Management intervention in ecosystems with degraded environmental services requires innovative resource management strategies that go beyond conventional restoration and conservation practices. We established a unique study that experimentally targeted extreme fire conditions during drought in humid subtropical and semi-arid ecoregions. In the southern Great Plains of North America, conventional restoration and conservation practices have been either historically ineffective or economically cost-prohibitive at restoring grass-dominated ecosystems following conversion to resprouting shrublands. Our aim was to assess the potential for extreme fire during drought to force the system along an alternate ecological trajectory from its current progression towards closed-canopy resprouting shrubland, something that conventional fire prescriptions have been unable to accomplish. We first tested the potential for high-intensity fires exhibiting extreme behaviour to disrupt the progression from grassland to shrubland. In both ecoregions, significant levels of mortality were observed for mature woody resprouters. As a result, densities were either maintained or reduced 3 years following extreme fire treatments, whereas resprouter densities continued to increase in areas that were not burned. A second interventionist approach involving extreme fire and herbicide treatment combinations was not supported. Interactions between prescribed extreme fire and herbicide did not significantly reduce resprouter densities more than using herbicide alone at either site. Synthesis and applications. Extreme fires during drought resulted in exceptionally high levels of mortality across all sizes of woody resprouters and limited recruitment, resulting in 35–55% lower densities of resprouters than in areas not burned. These findings counter prevailing scientific and management expectations, which are based largely on studies that impose tight controls over prescribed fire conditions and avoid extreme fire behaviour. Future interventions for controlling woody resprouters with fire may require rethinking the present ideology that extreme fire behaviour has no place in modern social–ecological landscapes.