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

Abstract

In many forested ecosystems, it is increasingly recognized that the probability of burning is substantially reduced within the footprint of previously burned areas. This self-limiting effect of wildland fire is considered a fundamental emergent property of ecosystems and is partly responsible for structuring landscape heterogeneity (i.e., mosaics of different age classes), thereby reducing the likelihood of uncharacteristically large fires in regions with active fire regimes. However, the strength and longevity of this self-limiting phenomenon is not well understood in most fire-prone ecosystems. In this study, we quantify the self-limiting effect in terms of its strength and longevity for five fire-prone study areas in western North America and investigate how each measure varies along a spatial climatic gradient and according to temporal (i.e., annual) climatic variation. Results indicate that the longevity (i.e., number of years) of the self-limiting effect ranges between 15 yr in the warm and dry study area in the southwestern United States to 33 yr in the cold, northern study areas in located in northwestern Montana and the boreal forest of Canada. We also found that spatial climatic variation has a strong influence on wildland fire's self-limiting capacity. Specifically, the self-limiting effect within each study area was stronger and lasted longer in areas with low mean moisture deficit (i.e., wetter and cooler settings) compared to areas with high mean moisture deficit (warmer and drier settings). Last, our findings show that annual climatic variation influences wildland fire's self-limiting effect: drought conditions weakened the strength and longevity of the self-limiting effect in all study areas, albeit at varying magnitudes. Overall, our study provides support for the idea that wildland fire contributes to spatial heterogeneity in fuel ages that subsequently mediate future fire sizes and effects. However, our findings show that the strength and longevity of the self-limiting effect varies considerably according to spatial and temporal climatic variation, providing land and fire managers relevant information for effective planning and management of fire and highlighting that fire itself is an important factor contributing to fire-free intervals.

Examining forest resilience to changing fire frequency in a fire‐prone region of boreal forest

“…To evaluate the potential effects of self‐regulation of area burned, we examined scenarios where flammability was 2‐times greater in stands older than 50 years than younger stands, consistent with empirical evidence in support of the self‐regulation hypothesis from results herein and research from Quebec (Erni et al, ; Héon et al, ) and Alberta (Beverly, ). The negative effect of time since fire on fire likely decreases as stands accumulate fuels over the 50 years following fire (Beverly, ; Parks, Parisien, Miller, Holsinger, & Baggett, ), and the scenario used here should estimate the maximum potential effect of self‐regulation on area burned. Nevertheless, our modeling results suggest this negative feedback was not great enough to counteract the effect of a climate change‐type increase in the probability of fire.…”

Fire regime on a cultural landscape: Navajo Nation

“…Second, spatially explicit sampling of fire regime patterns over large landscapes reveals detailed patterns that may not be detected by coarser or finer‐scale approaches. Burning patterns interact with climate variation over space and time to produce a self‐limiting effect on fire characteristics (Parks, Parisien, Miller, Holsinger, & Baggett, ) that may be critical to avoid fuel buildup resulting in large crown fires such as the Asaayi Lake fire. Even the largest fire event—1748—recorded at 41 of the 50 gridpoints (also the largest historical fire year in the entire Southwest, Swetnam & Brown, ) left behind a legacy of fire‐surviving scarred trees at nearly every sampling point on the 1 × 1 km grid, showing that this large fire was not “stand‐replacing.” In contrast, the Asaayi Lake fire burned 59.5 km 2 in the Chuska Mountains in 2014 with mostly lethal intensity, leaving large patches of complete tree mortality.…”

Wildland fire reburning trends across the US West suggest only short-term negative feedback and differing climatic effects

“…Climate and topography strongly influence recovering vegetation that ultimately fuels subsequent fires (Coppoletta et al 2016, Erni et al 2017, Grabinski et al 2017, Parks et al 2018 and climate (especially inter-annual moisture deficits, Westerling 2016) affects flammability as well. Extreme fire conditions, such as intense drought, can overwhelm negative feedbacks on burning associated with low fuel loads (Parks et al 2018, Tepley et al 2018, and increasing aridity will lead to increasing burn probabilities in many locations (Coppoletta et al 2016, Littell et al 2016, Keyser and Westerling 2017. Looking past the first fire, however, suggests that fuel limitations immediately after a burn will limit reburn activity-at least until the landscape regenerates biomass (Heon et al 2014, Coppoletta et al 2016).…”