Drought and fuel structure controls on fire severity. Effects on post-fire vegetation and soil carbon dynamics.

Grau Andres, Roger (2017) Drought and fuel structure controls on fire severity. Effects on post-fire vegetation and soil carbon dynamics. PhD thesis, University of Glasgow.

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Abstract

Calluna-dominated habitats, including dry heaths and peat bogs, provide
important ecosystem services such as biodiversity, soil carbon stores and water
supply. Climate change projections estimate drier conditions throughout their
range, which could lead to increased wildfire activity. Such altered fire regime
could induce a fundamental change to the ecology of Calluna moorlands
and increase carbon emissions from their carbon-rich soils. The aim of this
research was to understand how ecosystem response varies in relation to
increased fire severity in Calluna heathlands and peat bogs. I completed
experimental fires at two sites in Scotland, a dry heath and a raised bog, where
I manipulated pre-fire fuel structure and fuel moisture content to achieve a
gradient of fire severity and investigated the subsequent effect on post-fire
vegetation regeneration and soil carbon dynamics.
I found that drought increased fire severity in terms of ground fuel consumption
and soil heating through increased flammability of the moss and
litter layer. Substantially higher fire-induced ground heating was recorded
when this layer ignited. When consumption of the moss and litter layer
was extensive, post-fire soil thermal dynamics were altered and diurnal and
seasonal thermal variation was higher, resulting in warmer soils that may lead
to higher soil carbon emissions. Fire effects (ground fuel consumption, ground
heating, changes in post-fire soil thermal dynamics) were much stronger at
the dry heath than at the raised bog, likely due to ecohydrological differences
between sites, i.e. thicker moss layer and deeper, wetter soil at the raised bog.
For example, average fire-induced maximum temperatures at the soil surface at the dry heath increased from 31 degree C to 189 C due to drought, but at the
raised bog they increased from 10 C to 15 C.
Post-fire vegetation community composition varied in relation to the
gradient of fire severity at the dry heath. Higher fire severity increased
abundance of dominant ericoid species (Calluna vulgaris, Erica cinerea and
Erica tetralix ) through improved substrate conditions (consumption of the
moss and litter layer leading to bare soil), despite the fact that higher fire-induced soil heating hindered their regeneration.
Short-term soil carbon emissions increased after burning due to a greater
reduction in photosynthesis than in ecosystem respiration. Methane fluxes
were negligible at the dry heath, but increased after burning at the raised
bog, especially in warmer conditions. Generally, higher fire severity had little
effect on soil carbon dynamics (ecosystem respiration, net ecosystem exhange,
methane flux and dissolved organic carbon concentration), but higher autumn
emission after higher fire severity at the dry heath and the important control
of plant functional type cover suggest differences may become apparent in
the longer term.
This research advances our understanding of how an altered fire regime
with higher fire severity could alter ecosystem functioning in Calluna moorlands
and impact on its conservation value and belowground carbon stores.
The work presented here can be useful to managers using burning as a land
management tool, or who need to plan for wildfire occurrence in these fire-prone habitats, to inform strategies to accomplish a range of objectives,
including conservation, protection of carbon stores and recreation, and to
researchers interested in environmental change in Calluna moorlands.
This research was funded by the University of Glasgow with support from
the Centre for Ecology and Hydrology, the Ohio State University and Glen
Tanar Estate.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Calluna, heathland, moorland, peatland, fire, wildfire, prescribed burning, muirburn, fire behaviour, vegetation regeneration, respiration, photosynthesis, net ecosystem exchange.
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Q Science > Q Science (General)
Q Science > QK Botany
Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
Supervisor's Name: Waldron, Professor Susan
Date of Award: 2017
Depositing User: Dr Roger Grau Andres
Unique ID: glathesis:2017-7929
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 13 Feb 2017 13:13
Last Modified: 09 Feb 2018 09:55
URI: http://theses.gla.ac.uk/id/eprint/7929

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