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Where fire stops: vegetation structure and microclimate influence fire spread along an ecotonal gradient

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Positive feedbacks influenced by direct and indirect interactions between fire, vegetation, and microclimate can allow pyrophilic and pyrophobic ecosystems to co-occur in the same landscape, resulting in the juxtaposition of flammable and non-flammable vegetation. To quantify the drivers of these feedbacks, we combined measurements of vegetation, fuels, and microclimate with observations of fire spread along ecotonal gradients. We established 113 permanent transects (consisting of 532 plots), each traversing an ecotone between savanna and wetland in the Sandhills of North Carolina, USA. In each plot, we recorded cover of ten plant functional types. We collected surface fuels at a subset of our transects. We continuously monitored microclimate (nine meteorological variables) across 21 representative ecotones. Following prescribed fire, we measured fire spread along each transect. Vegetation structure and microclimate significantly predicted fire spread along the savanna-wetland ecotone. Fire spread was most influenced by vegetation structure, specifically C-4 grass cover, which accounted for 67 % of the variance explained by our model. We have identified the components of the fire, vegetation, and microclimate feedback that control where fires stop under current conditions, but their control should not be considered absolute. For example, when ignited in savanna, prescribed burns continued through wetland vegetation 43 % of the time. The feedback operating within these systems may be relatively weak as compared to other savanna systems. Environmental changes may alter fire spread extent, and with it ecosystem boundaries, or even ecosystem states.
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Where fire stops: vegetation structure and microclimate
influence fire spread along an ecotonal gradient
Michael G. Just .Matthew G. Hohmann .
William A. Hoffmann
Received: 22 July 2015 / Accepted: 16 November 2015 / Published online: 23 November 2015
ÓSpringer Science+Business Media Dordrecht 2015
Abstract Positive feedbacks influenced by direct
and indirect interactions between fire, vegetation, and
microclimate can allow pyrophilic and pyrophobic
ecosystems to co-occur in the same landscape, result-
ing in the juxtaposition of flammable and non-
flammable vegetation. To quantify the drivers of these
feedbacks, we combined measurements of vegetation,
fuels, and microclimate with observations of fire
spread along ecotonal gradients. We established 113
permanent transects (consisting of 532 plots), each
traversing an ecotone between savanna and wetland in
the Sandhills of North Carolina, USA. In each plot, we
recorded cover of ten plant functional types. We
collected surface fuels at a subset of our transects. We
continuously monitored microclimate (nine meteoro-
logical variables) across 21 representative ecotones.
Following prescribed fire, we measured fire spread
along each transect. Vegetation structure and micro-
climate significantly predicted fire spread along the
savanna-wetland ecotone. Fire spread was most influ-
enced by vegetation structure, specifically C
4
grass
cover, which accounted for 67 % of the variance
explained by our model. We have identified the
components of the fire, vegetation, and microclimate
feedback that control where fires stop under current
conditions, but their control should not be considered
absolute. For example, when ignited in savanna,
prescribed burns continued through wetland vegeta-
tion 43 % of the time. The feedback operating within
these systems may be relatively weak as compared to
other savanna systems. Environmental changes may
alter fire spread extent, and with it ecosystem bound-
aries, or even ecosystem states.
Keywords Feedback Fire ecology Longleaf pine
Savanna Streamhead pocosin Wetland
Introduction
Understanding the role of fire in controlling the
distribution of vegetation is complicated by positive
feedbacks that commonly exist between vegetation
and fire (Murphy and Bowman 2012; Fill et al. 2015).
Within these feedbacks, vegetation structure (i.e.,
physical structure and species composition) influences
Communicated by Prof. Michael Lawes, Prof. Ross Bradstock,
and Prof. David Keith.
Electronic supplementary material The online version of
this article (doi:10.1007/s11258-015-0545-x) contains supple-
mentary material, which is available to authorized users.
M. G. Just (&)W. A. Hoffmann
Department of Plant and Microbial Biology, North
Carolina State University, Raleigh, NC 27695, USA
e-mail: mjust@ncsu.edu
M. G. Hohmann
US Army Corps of Engineers, Engineer Research and
Development Center, P.O. Box 9005, Champaign,
IL 61826, USA
123
Plant Ecol (2016) 217:631–644
DOI 10.1007/s11258-015-0545-x
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