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Disturbance and perturbations

April 18th, 2019 Leave a comment Go to comments

Fire is a key process in many ecosystem (fire-prone ecosystems), where it is best viewed as a natural disturbance that benefits to ecosystem functioning. However, increasingly, we are seeing human interference in fire regimes that alters the historical range of variability for most fire parameters and results in vegetation shifts. Such perturbations can affect all fire regime parameters. In a recent paper [1] we provide a brief overview of examples where anthropogenically driven changes in fire frequency, fire pattern, fuels consumed and fire intensity constitute perturbations that greatly disrupt natural disturbance cycles and put ecosystems on a different trajectory resulting in type conversion. These changes are not due to fire per se but rather anthropogenic perturbations in the natural disturbance regime. That is, the critical factor determining system resilience is not fire but the perturbations of fire regime. Of course, in ecosystems where fire is not a natural process (e.g., rainforests), we should consider fire itself to be a perturbation.

Examples of perturbations of the fire regime, specifically alterations of the fire interval:


Entire chaparral landscape in the frame burned in 1970, half of the foreground burned again in 2001 and the far right third of the foreground burned a third time in 2003, all by human-caused ignitions. Vegetation recovery following the 2001 fire comprises native shrub and subshrub regeneration, those areas burned a third time in 2003 are dominated by alien red brome grass invasion (photo by R. W. Halsey [1]).

 


Massive lodgepole (Pinus cortata) forest regeneration following the 1988 North Fork Fire, which burned over 200.000 ha of Yellowstone lodgepole forests, was partially reburned after 28 years in the 2016 Maple Fire of 18.200 ha. This atypical short interval resulted in very little regeneration (immaturity risk); casual observations in the summer of 2018 revealed, 10 to 1 ratio of adult skeletons to seedlings, clearly not stand-replacing recruitment (photo by J. E.Keeley [1]).

 

References

[1] Keeley J.E. & Pausas J.G. 2019. Distinguishing disturbance from perturbations in fire-prone ecosystems. Int. J. Wildland Fire [doi | IJWF | pdf]

 

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