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Alternative community states maintained by fire in the Klamath Mountains, USA

Alternative community states maintained by fire in the Klamath Mountains, USA Summary 1. The earliest examples of alternative community states in the literature appear to be descriptions of natural vegetation said to both depend on and promote fire. Nonetheless, alternative community states determined by fire have rarely been documented at landscape scales and in natural vegetation. This is because spatial autocorrelation may confound analyses, experimental manipulations are difficult and a long‐term perspective is needed to demonstrate that alternative community states can persist for multiple generations. 2. We hypothesized that alternative community states occur in a largely forested landscape in the Klamath Mountains, north‐western California, USA, where shrub‐dominated sclerophyllous vegetation establishes after fire that is lethal to forests. Forests redevelop if succession is not arrested by fire. Our hypothesis would require that sclerophyll and forest vegetation states each be maintained by different self‐reinforcing relationships with fire. 3. To test this hypothesis, we examined pyrogenicity of forest and sclerophyll vegetation as a function of time since the previous fire, accounting for spatial autocorrelation. Fire exclusion served as a de facto experimental treatment. Areas where fire had proceeded to occur served as controls. 4. Our findings are consistent with the occurrence of alternative community states established and maintained by different self‐reinforcing feedbacks with fire. Sclerophyll vegetation was more pyrogenic, especially where time‐since‐fire (TSF) was relatively short, a favourable relationship for this fire‐dependent vegetation. Forests were much less pyrogenic, especially where TSF was long, favouring their maintenance. Fire exclusion therefore has led to afforestation and rapid retreat of fire‐dependent vegetation. 5. Synthesis: We have documented how different self‐reinforcing combustion properties of forest and sclerophyll vegetation can naturally produce alternative states coexisting side‐by‐side in the same environment. Such fire‐mediated alternative states may be underappreciated, in part, because they are difficult to demonstrate definitively. In addition, the dynamics they exhibit contrast with common perceptions that fire hazard increases deterministically with TSF in forests and shrublands. Addressing the impacts of fire exclusion will probably require a management shift to better allow fire to perform its ecological role in shaping landscape diversity and maintaining fire‐dependent biota. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Ecology Wiley

Alternative community states maintained by fire in the Klamath Mountains, USA

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References (103)

Publisher
Wiley
Copyright
© 2009 The Authors. Journal compilation © 2009 British Ecological Society
ISSN
0022-0477
eISSN
1365-2745
DOI
10.1111/j.1365-2745.2009.01597.x
Publisher site
See Article on Publisher Site

Abstract

Summary 1. The earliest examples of alternative community states in the literature appear to be descriptions of natural vegetation said to both depend on and promote fire. Nonetheless, alternative community states determined by fire have rarely been documented at landscape scales and in natural vegetation. This is because spatial autocorrelation may confound analyses, experimental manipulations are difficult and a long‐term perspective is needed to demonstrate that alternative community states can persist for multiple generations. 2. We hypothesized that alternative community states occur in a largely forested landscape in the Klamath Mountains, north‐western California, USA, where shrub‐dominated sclerophyllous vegetation establishes after fire that is lethal to forests. Forests redevelop if succession is not arrested by fire. Our hypothesis would require that sclerophyll and forest vegetation states each be maintained by different self‐reinforcing relationships with fire. 3. To test this hypothesis, we examined pyrogenicity of forest and sclerophyll vegetation as a function of time since the previous fire, accounting for spatial autocorrelation. Fire exclusion served as a de facto experimental treatment. Areas where fire had proceeded to occur served as controls. 4. Our findings are consistent with the occurrence of alternative community states established and maintained by different self‐reinforcing feedbacks with fire. Sclerophyll vegetation was more pyrogenic, especially where time‐since‐fire (TSF) was relatively short, a favourable relationship for this fire‐dependent vegetation. Forests were much less pyrogenic, especially where TSF was long, favouring their maintenance. Fire exclusion therefore has led to afforestation and rapid retreat of fire‐dependent vegetation. 5. Synthesis: We have documented how different self‐reinforcing combustion properties of forest and sclerophyll vegetation can naturally produce alternative states coexisting side‐by‐side in the same environment. Such fire‐mediated alternative states may be underappreciated, in part, because they are difficult to demonstrate definitively. In addition, the dynamics they exhibit contrast with common perceptions that fire hazard increases deterministically with TSF in forests and shrublands. Addressing the impacts of fire exclusion will probably require a management shift to better allow fire to perform its ecological role in shaping landscape diversity and maintaining fire‐dependent biota.

Journal

Journal of EcologyWiley

Published: Jan 1, 2010

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