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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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
Funder's Name: UNSPECIFIED
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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