Environmental drivers of large, infrequent wildfires: the emerging conceptual model

Abstract

Large, infrequent fires (LIFs) can have substantial impacts on both ecosystems and the economy. To better understand LIFs and to better predict the effects of human management and climate change on their occurrence, we must first determine the factors that produce them. Here, we review local and regional literature investigating the drivers of LIFs. The emerging conceptual model proposes that ecosystems can be typified based on climatic conditions that determine both fuel moisture and fuel amount. The concept distinguishes three ecosystem types: (1) biomass-rich, rarely dry ecosystems where fuel moisture rather than fuel amount limits LIFs; (2) biomass-poor, at least seasonally dry ecosystems where fuel amount rather than fuel moisture limits LIFs; and (3) biomass-poor, rarely dry ecosystems where both fuel amount and fuel moisture limit the occurrence of LIFs. Our main goal in this paper is to discuss the drivers of LIFs and the three mentioned ecosystem types in a global context. Further, we will discuss the drivers that are not included within the `fuels' versus `climate' discussion. Finally, we will address the question: what kinds of additional information are needed if models predicting LIFs are to be coupled with global climate models? As with all generalizations, there are local deviations and modifications due to processes such as disturbance interaction or human impact. These processes tend to obscure the general patterns of the occurrence of LIFs and are likely to cause much of the observed controversy and confusion in the literature.

Relationships between annual plant productivity, nitrogen deposition and fire size in low-elevation California desert scrub

“…This biomass threshold is at the higher end of the range of fine fuel thresholds of 70-150 g m À2 reported as being able to carry fire in grass-dominated systems (Anderson 1982;Scifres and Hamilton 1993;Fenn et al 2003a). For reasons already discussed, no biomass threshold appeared to influence most of the fire size distribution, although the change in fire size at the 99th percentile of the fire size distribution when fine fuel loads exceeded 125 g m À2 does support the hypothesis that annual biomass production above a certain threshold creates a continuous fine fuel load that facilitates fire spread and is necessary for the occurrence of large fires in a low-elevation desert ecosystem that would otherwise be fuel limited (Brown and Minnich 1986;Brooks and Matchett 2006;Meyn et al 2007).…”

Defining Extreme Wildfire Events: Difficulties, Challenges, and Impacts

“…Fernandes et al [24] consider a minimum threshold of 2,500 ha, equivalent to the 99.9 th percentile of fire size in Portugal, to be an ELF. Meyn et al [47] prefer the term large infrequent fires to label the events that are exceptional in their large spatial size, if compared with the fires that usually affect the ecosystems. Schmoldt et al [48] use the term extensive fire to describe very large wildfires, without reference to specific fire features.…”

Predictability of biomass burning in response to climate changes

“…If this is indeed the case, a key issue is whether there is further potential for landscape fragmentation to offset climateinduced increases in fire in the future [see, e.g., Kloster et al, 2012] given that over 75% of the land area is considered to already be impacted by human activities [Ellis and Ramankutty, 2008]. The large number of regional studies documenting increases in fires in the last two decades [e.g., Barlow and Peres, 2004;Cary, 2002;Gillett et al, 2004;Groisman et al, 2007;Kajii et al, 2002;Meyn et al, 2007;Le Page et al, 2007;Pausas et al, 2008;Soja et al, 2007;Stocks et al, 2003;Westerling et al, 2006;Williams et al, 2010] suggest that we may already have reached the point at which landscape fragmentation is not an effective means of fire suppression, and indeed these recent increases have been explicitly linked to global warming [Running, 2006;Soja et al, 2007] Indeed, projections of future fire activity by Pechony and Shindell [2010] show an increase in global fire activity with warming that is not offset by human influences on ignitions or land use.…”