Spatial bottom‐up controls on fire likelihood vary across western North America

Abstract

Abstract. The unique nature of landscapes has challenged our ability to make generalizations about the effects of bottom-up controls on fire regimes. For four geographically distinct fire-prone landscapes in western North America, we used a consistent simulation approach to quantify the influence of three key bottom-up factors, ignitions, fuels, and topography, on spatial patterns of fire likelihood. We first developed working hypotheses predicting the influence of each factor based on its spatial structure (i.e., autocorrelation) in each of the four study areas. We then used a simulation model parameterized with extensive fire environment data to create high-resolution maps of fire likelihood, or burn probability (BP). To infer the influence of each bottom-up factor within and among study areas, these BP maps were compared to parallel sets of maps in which one of the three bottom-up factors was randomized. Results showed that ignition pattern had a relatively minor influence on the BP across all four study areas, whereas the influence of fuels was large. The influence of topography was the most equivocal among study areas; it had an insignificant influence in one study area and was the dominant control in another. We also found that the relationship between the influence of these factors and their spatial structure appeared nonlinear, which may have important implications for management activities aimed at attenuating the effect of fuels or ignitions on wildfire risk. This comparative study using landscapes with different biophysical and fire regime characteristics demonstrates the importance of employing consistent methodology to pinpoint the influence of bottom-up controls.

Environmental Influences on Forest Fire Regime in the Greater Hinggan Mountains, Northeast China

“…The interaction of top-down and bottom-up factors governs forest fire regimes over a range of spatial and temporal scales. The bottom-up controls usually act at fine scales by regulating fire physics and behavior [8]. For instance, fire propagation is mainly controlled by weather, local terrain plus fuel load, moisture content, and fuel continuity.…”

Quantifying influences and relative importance of fire weather, topography, and vegetation on fire size and fire severity in a Chinese boreal forest landscape

“…Fire weather is considered a top-down control as its impacts on fire are described at a broad spatial extent. Topography and fuel conditions are usually considered bottom-up controls as their impacts on fire activity are spatially more variable (Cyr et al, 2007;Parks et al, 2012). It has been demonstrated that the relationship between fire activity and patterns of fire-induced ecological consequences could exhibit nonlinearities across a gradient of spatial scales due to interactions between top-down and bottom-up controls (Peters et al, 2004(Peters et al, , 2007.…”

Fine‐scale spatial climate variation and drought mediate the likelihood of reburning

“…In light of increasing fire activity and ever-growing fire-suppression expenditures (Calkin et al 2015), it is imperative that we understand how wildland fire influences subsequent disturbance processes. In addition, improved knowledge of what factors (i.e., spatial and temporal variation in climate) enhance or constrain wildland fire's self-limiting effect could also be useful to those who model fire likelihood and risk across large landscapes (Finney et al 2011, Parisien et al 2011, Parks et al 2012) and potentially inform efforts to predict fire activity under a warming climate (Batllori et al 2013, McKenzie and Littell 2017, Parks et al 2017. Miller 2003, North et al 2012, Hessburg et al 2015.…”