Vegetation, terrain and fire history shape the impact of extreme weather on fire severity and ecosystem response

Abstract

Questions Do endogenous (landscape/vegetation) or exogenous (weather) factors control fire severity? During severe fire weather, is there convergence in fire severity across rain forest, forests and heathlands such that all locations burn with similarly high severity? Are there long‐term effects of fire severity in temperate crown‐fire ecosystems? Location Montane rain forests, eucalypt forests and heaths in the temperate climate zone of eastern Australia (Washpool/Gibraltar Range National Park). Methods The immediate and longer‐term effects of fire weather and landscape (terrain, previous fire history and vegetation type) factors on fire severity and ecosystem response were measured using remote sensing and ground measures of microclimate, productivity and plant resprouting at 45 sites. Results Fire weather strongly interacted with terrain, antecedent fire history and vegetation type, resulting in complex mosaics of mixed fire severity rather than convergence to uniform fire severity. Vegetation type influenced the effects of time‐since‐fire and fire frequency on fire severity, suggesting differential fire feedbacks. High fire severity left a long‐term imprint on total reflectance, ground temperatures and productivity of the vegetation, but these effects were not uniform across vegetation types. The abundance of resprouting species was not strongly affected by fire severity. Conclusions There was evidence for strong weather control of fire severity but fire history, terrain and vegetation shape the immediate effect due to the contrasting pyrogenic vs pyrophobic nature of the vegetation mosaic. The short‐term dominance of weather as a driver of fire severity is only weakly related to the longer‐term ecosystem response because of the strong resprouting ability of the canopy dominants, even in rain forest. The forest complexes of eastern Australia appear highly resilient to high fire severity in both structure and floristics, which may influence long‐term feedbacks.

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

“…As an example, Miller et al (2012) found increased trends of mean and maximum burned patch size from 1910 to 2008 in the western US, but did not find clear temporal trends of fire severity from 1987 to 2008. Within cool, moist forest ecosystems that belong to the low-and mixed-severity fire regimes, the local bottom-up controls may continue to be important in regulating fire severity even though warmer climate is conducive to larger burns (Cansler and McKenzie, 2014;Clarke et al, 2014). Large high-severity fires will become frequent only if a sufficient existence of coinciding factors such as high fuel continuity and fuel loading, the more frequent and severe drought, and increasing variability in seasonal precipitation (Margolis and Balmat, 2009;O'Connor et al, 2014).…”

“…However, future trends of fire severity may be not as predictable as future trends of fire size. Relationships between fire severity and both short-term severe fire weather and long-term warming climate are weak and tend to be mediated by terrain, vegetation composition and fire history (Clarke et al, 2014;Cansler and McKenzie, 2014). Previous studies have confirmed pre-fire stand conditions such as tree density, canopy coverage, the average stand diameter, and beetle outbreak history to have notable influences on spatial patterns of fire severity (Turner et al, 1999;Bigler et al, 2005;Alexander et al, 2006;Lentile et al, 2006b).…”

“…However, since fire severity has mainly been described at site and stand scales (French et al, 2008;Key and Benson 2006), previous studies primarily focused on characterizing influences of bottom-up controls (Alexander et al, 2006;Lentile et al, 2006b;Holden et al, 2009;Wu et al, 2013a) and contributions of climate and fire weather were seldom discussed (but see Cansler and McKenzie, 2014;Dillon et al, 2011;Parks et al, 2014a). Despite recent studies suggesting that topographic variables are more important than climate or fire weather in driving severe fire occurrence in the western US (Dillon et al, 2011) and eastern Australia (Clarke et al, 2014), there is a lack of understanding concerning whether severity patterns in boreal regions also possess this regulation mechanism. Recent studies have indicated the relative contributions of environmental controls on fire size may vary substantially among spatial scales (Parisien et al, 2011;Liu et al, 2013).…”

Wildfire refugia in forests: Severe fire weather and drought mute the influence of topography and fuel age

“…the consumption of organic matter; Keeley, ), which is driven by complex interactions between weather, fuels and topography (e.g. Bradstock, Hammill, Collins, & Price, ; Clarke, Knox, Bradstock, Munoz‐Robles, & Kumar, ). Fire severity and the spatial patterns of severity classes (e.g.…”

Mapping and exploring variation in post‐fire vegetation recovery following mixed severity wildfire using airborne LiDAR

“…It can be measured in the field or from remote sensing using multi-spectral indices that describe blackening (Hammill and Bradstock 2006). Also, studies have found that high-severity fires often have minimal effects on vegetation diversity, including in North American pine forests and west coast shrublands (Turner et al 1999, Purdon et al 2004, Keeley et al 2008, Fornwalt and Kaufmann 2014 and Australian eucalypt forests (Bradstock 2009, Knox and Clarke 2012, Camac et al 2013, Clarke et al 2014. However, there is increasing evidence that some floristic elements are favored by high-severity fires because these fires are required to trigger seed germination (Ooi et al 2006, Liyanage andOoi 2015).…”