Pyric-herbivory

archived

Our overall goal is to evaluate the conceptual model proposed by Fuhlendorf and Engle (2001) and determine role of fire in altering grazing behavior of native herbivores to create a shifting mosaic that is critical to grassland conservation and management. The pyric-herbivory model suggests an alternative perspective where fire and grazing are largely interactive in space and time. This model is largely driven by positive and negative feedbacks. Positive feedbacks occur where fire promotes site selection by herbivores (Figure 1D). This is a positive feedback because one disturbance increases the likelihood of another disturbance. A negative feedback also occurs where areas burned and graze result in lower fuel accumulation reducing the probability and intensity of fire (Figure 1C). This model is fairly intuitive but we know little about the strength of these feedbacks or the effects of the interaction of the two disturbance processes. We are proposing an innovative approach based on global positioning systems (GPS) technology to understand pyric-herbivory that is critical to many fire and grazing-dependent ecosystems across the world. Our approach will allow us to study the feedback mechanisms and the interactive effects that result in highly variable patterns in space and time. In evaluating this goal we will address the following objectives: 1. Determine the strength of feedback mechanisms associated with herbivore selection following fires. 2. Determine the strength of feedback mechanisms associated with probability and intensity of fire. 3. Evaluate the effects of pyric-herbivory when applied with multiple herbivores. Understanding fire and grazing in the context of pyric-herbivory requires a new paradigm for experimental design (Figure 1b). Specifically, we hypothesize that much of understanding of fire and grazing is limited by our experimental design. Understanding the roles of spatial and temporal heterogeneity and disturbance feedbacks may change many of our generalizations. An alternative, heterogeneity-based paradigm suggests that herbivores must be able to select from a diverse landscape that is variable in season and time since fire. This complex landscape will then become more complex as fire and grazing start to interact in space and time. This will require a multiscale approach where landscape patterns and plot level studies are evaluated simultaneously with a focus on heterogeneity rather than uniform treatment effects.

High