Abstract
The role of fire in the maintenance of oak-dominated ecosystems is widely recognized. Fire exclusion results in structural and compositional shifts that alter fuelbed composition and structure, together influencing fire behavior and effects. To clarify the influence of overstory structure on fuels and fire intensity in oak woodlands and savannas, we examined fuelbeds across a gradient from open grassland to Douglas-fir- (Pseudotsuga menziesii (Mirb.) Franco) invaded Oregon white oak (Quercus garryana Douglas ex Hook.) woodland in the Bald Hills of Redwood National Park, California, USA. Herbaceous mass decreased markedly from a high in grasslands (3.38 Mg ha−1) to a low in invaded woodlands (0.03 Mg ha−1), whereas leaf litter and woody fuel mass increased substantially along this gradient. Mean fire temperatures at 30 cm height ranged from 74.7 °C in invaded woodland up to 207.9 °C in grassland. Highly flammable grassland and savanna communities maintain heavy herbaceous mass, but low woody mass, favoring quick-spreading, relatively high-intensity fires. The encroachment of Douglas-fir into grasslands and oak-dominated communities dampens flammability through changes in fuelbed composition and structure (e.g., the replacement of herbaceous fuels with woody fuels), underscoring the necessity for ecological restoration efforts that focus on fuelbed structure in addition to other common restoration goals.
Highlights
Fire influences the structure and composition of savanna and woodland ecosystems worldwide (e.g., Higgins et al 2000, Peterson and Reich 2001, Hoffmann and Solbrig 2003, Bond and Keeley 2005)
In the Pacific Northwest region of the US, fire exclusion has resulted in a suite of structural and compositional changes in Oregon white oak (Quercus garryana Dougl. ex Hook.) woodlands and other plant communities
Lawson) in the southwestern United States (Abella and Fulé 2008), savannas of northeastern South Africa (Govender et al 2006), and Brazilian cerrado (Hoffman 1999), among others. Plant modifications to their immediate environment that lead to differential flammability has been termed niche construction (Schwilk 2003), and recruitment of fire-sensitive species in these fire-prone environments may be mediated by fire intensity generated by flammable fuels provided by firefacilitating species (e.g., Rebertus and Burns 1997, Fonda 2001, Hoffman et al 2003, Kane et al 2008, Beckage et al 2009)
Summary
Fire influences the structure and composition of savanna and woodland ecosystems worldwide (e.g., Higgins et al 2000, Peterson and Reich 2001, Hoffmann and Solbrig 2003, Bond and Keeley 2005). Lawson) in the southwestern United States (Abella and Fulé 2008), savannas of northeastern South Africa (Govender et al 2006), and Brazilian cerrado (Hoffman 1999), among others Plant modifications to their immediate environment that lead to differential flammability has been termed niche construction (Schwilk 2003), and recruitment of fire-sensitive species in these fire-prone environments may be mediated by fire intensity generated by flammable fuels provided by firefacilitating species (e.g., Rebertus and Burns 1997, Fonda 2001, Hoffman et al 2003, Kane et al 2008, Beckage et al 2009). Findings of this study offer particular relevance to managers faced with the invasion of fire-sensitive species in fireprone ecosystems, documenting how community structure alters fuelbeds and, the ability of managers to meet restoration objectives with managed fire
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