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Toward an understanding of how indirect effects of fire may affect management outcomes

By Dr. Marcus Lashley, Mississippi State University

December 4, 2018 at 1:00 PM central

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Abstract: We as fire enthusiast commonly think of fire as a management tool that can be used to decrease fuel loads, or improve wildlife habitat and forest regeneration success. However, we often focus only on direct effects and fail to consider the complexity of how fire influences biological interactions which can in turn, indirectly affect the outcome of the fire. In this webinar, I will report on a series of experiments conducted in various fire-maintained ecosystems that demonstrate that characteristics of prescribed fire influence herbivore behavior and herbivore behavior can transmit the indirect effects of fire to plant communities. Though there are entire food webs of interactions that can influence the outcome of fire, I will focus on fire-herbivory interactions because most practitioners view herbivory as a nuisance, fire and herbivory have a close relationship in all fiery ecosystems, and their interaction is important to the outcome of a burn. The release of resources following fire in regenerating plants causes a magnet-effect for herbivores which occurs even at very small scales of burning. The nature of the fire-herbivory interaction is dependent of fire phenology because it dictates the magnitude and timing of the resource pulse for herbivores. When fire phenology is such that the subsequent resource pulse closely aligns with herbivore nutritional demands, a series of behavioral changes occur that are important for the outcome of the fire. That is, when the resource pulse co-occurs with herbivore nutritional demands, herbivore diet preferences shift away from herbaceous plants to focus on vigorously resprouting hardwoods, most of which are undesirable species for most objectives of fire management. Simultaneously, the magnet effect coupled with strong preference for those species, slows regeneration of undesirable hardwoods and makes them more vulnerable to subsequent fires. As a result, both fire and herbivory independently homogenize plant communities, but their interaction increases heterogeneity across sites. The strong herbivory pressure on regenerating hardwoods also delays leaf maturation which increases the rate of leaf decomposition in the fall, decreasing subsequent fuel loads and increasing nutrient turnover rate. Because herbivory is focused on faster growing hardwoods, slower growing oak species may gain a competitive advantage potentially increasing the success of regeneration. When fires are timed so that resource pulses and herbivore demands do not align, the magnet effect and preference shift are weakened, and the aforementioned benefits of herbivory after fire are lost. Our understanding of the importance of indirect effects of fire on plant community succession is still in its infancy, but results from these experiments indicate they may explain some of the hard-to-predict context-dependence of prescribed fire.