Successional theory as it relates to fire effects and forest conversion.
Christensen, Norman1, 1 Duke University, Durham, NC, USA
ABSTRACT- One of the earliest papers on fire effects and post-fire succession was written by none other than Frederic Clements, and for many decades thereafter, fire and the patterns of change it initiated were interpreted as an exemplar of the classical model of directional succession. With the recognition that post-fire vegetation change in some ecosystems may actually produce flammable conditions that ensure the next fire event, linear, notions of cyclic succession and pulse stability became fashionable. Although directional and cyclic models of succession remain useful in interpreting fire effects and post-fire change in different systems, neither model is adequate to describe the full range of variation in fire behavior and post-fire response, and ecologists are today inclined toward more probabilistic patch-mosaic successional models in which fire is understood to behave along gradients of size, severity and frequency. Variations in behavior interact with the environmental mosaic to produce varying patterns of ecosystem response. Rather than end points or mean return times, these models focus attention on historic and likely future range of variation (HRV and FRV) and the concept of minimum dynamic area. Much recent attention has been dedicated to factors such as climate change, invasive alien species and catastrophic fire that produce state changes (e.g., forest to non-forest) that appear to be outside the HRV, and terms such as multiple stable points, meta-stability and state-change threshold have been added to the successional lexicon. The value of this framework for understanding fire-related conversion of forest to non-forest will be discussed.
Key words: historic range of variation, state change, threshold
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