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URI [dataset] UNIVERSITY OF SOUTHAMPTON FACULTY OF SOCIAL, HUMAN AND MATHEMATICAL SCIENCES Geography and Environment Volume 1 of 1 Blanket peatland carbon dynamics: palaeoenvironmental contributions to the land use debate by Robert Charles Collier Thesis for the degree of Doctor of Philosophy November 2017 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF SOCIAL, HUMAN AND MATHEMATICAL SCIENCES Geography and Environment Thesis for the degree of Doctor of Philosophy BLANKET PEATLAND CARBON DYNAMICS: PALAEOENVIRONMENTAL CONTRIBUTIONS TO THE LAND USE DEBATE Robert Charles Collier Blanket peatlands are the most efficient UK terrestrial habitat for carbon storage and their protection is essential to meet greenhouse gas reduction targets. ‘Carbon conscious’ management seeks to manage the ecosystem specifically to maintain or enhance future carbon sequestration. Uncertainty over the impact of land use on blanket peatland carbon sequestration hampers attempts to manage the ecosystem in a sustainable manner. This thesis addresses both the poor understanding of the relationship between land use and carbon accumulation and the lack of palaeoenvironmental records which assess the integrity of Welsh blanket peatlands. A suite of dating techniques are used to reconstruct carbon accumulation rates across a range of peatlands. Data are combined with plant macrofossil results to offer insight into how land use has affected peatland development. Reported results emphasize that management cannot be considered a constant, linear forcing on blanket peatland development. An alternative method for examining the impacts of land management is presented, namely focussing on the cumulative expression of land management as manifested in vegetation records. Results suggest Sphagnum-dominated sites exhibit the most favourable conditions for carbon accumulation and the expansion of Molinia caerulea should be of concern to a carbon conscious peatland manager. Future directions for research are also discussed in light of the demonstrated fixation of the land use debate on comparatively recent anthropogenic impacts (i.e. post-AD 1850). Table of Contents Table of Contents ....................................................................................................................i Table of Tables ...................................................................................................................... ix Table of Figures ................................................................................................................. xiii Academic Thesis: Declaration Of Authorship .................................................. xxix Acknowledgements ........................................................................................................ xxxi Definitions and Abbreviations ................................................................................ xxxv Chapter 1 Introduction...................................................................................................... 1 1.1 Project rationale ................................................................................. 1 1.2 Project aim ......................................................................................... 3 1.3 Thesis structure ................................................................................. 4 1.4 Notes on terminology ........................................................................ 4 1.4.1 Peatland classification ................................................................ 4 1.4.2 Intact condition ........................................................................... 7 1.4.3 National Vegetation Classification .............................................. 8 Chapter 2 Literature review ........................................................................................ 11 2.1 Introduction ..................................................................................... 11 2.2 Blanket peatland carbon dynamics .................................................. 12 2.2.1 Blanket peatland ecosystems .................................................... 12 2.2.1.1 Blanket peatland formation and development .................. 12 2.2.1.2 Blanket peatlands and land management .......................... 16 2.2.1.3 An ecosystem services framework to promote sustainable management ...................................................................... 18 2.2.1.4 Palaeoenvironmental contributions to land management policy .................................................................................. 21 2.2.2 The carbon accumulation process ............................................ 21 2.2.3 Measuring peatland carbon dynamics ...................................... 26 2.2.4 Controls on carbon accumulation ............................................ 31 2.2.4.1 Plant community structure ................................................. 31 2.2.4.2 Water table position ........................................................... 34 2.2.4.3 Peat matrix characteristics ................................................. 35 i 2.2.4.4 Chemical composition of plant tissues and peat .............. 37 2.2.5 Section summary ...................................................................... 38 2.3 Impacts of burning on carbon accumulation .................................. 38 2.3.1 Background to the use of burning in blanket peatland management ........................................................................ 38 2.3.2 The effect of burning on plant community structure .............. 41 2.3.3 The effect of burning on water table position ......................... 44 2.3.4 The effect of burning on peat matrix characteristics .............. 45 2.3.5 The effect of burning on the chemical composition of plant tissues and peat ................................................................... 46 2.3.6 Section summary ...................................................................... 46 2.4 Impacts of drainage on carbon accumulation ................................. 47 2.4.1 Background to the use of drains in blanket peatland management ........................................................................ 47 2.4.2 The effect of drainage on plant community structure ............. 48 2.4.3 The effect of drainage on water table position ........................ 49 2.4.4 The effect of drainage on peat matrix characteristics ............. 50 2.4.5 The effect of drainage on the chemical composition of plant tissues and peat ................................................................... 52 2.4.6 Section summary ...................................................................... 52 2.5 Impacts of forestry on carbon accumulation .................................. 53 2.5.1 Background to the use of forestry in blanket peatland management ........................................................................ 54 2.5.2 The effect of forestry on plant community structure .............. 55 2.5.3 The effect of forestry on water table position ......................... 57 2.5.4 The effect of forestry on peat matrix characteristics............... 58 2.5.5 The effect of forestry on the chemical composition of plant tissues and peat ................................................................... 59 2.5.6 Section summary ...................................................................... 59 2.6 Impacts of grazing on carbon accumulation .................................. 60 2.6.1 Background to the use of grazing in blanket peatland management ........................................................................ 60 ii 2.6.2 The effect of grazing on plant community structure ............... 63 2.6.3 The effect of grazing on water table position .......................... 66 2.6.4 The effect of grazing on peat matrix characteristics ............... 66 2.6.5 The effect of grazing on the chemical composition of plant tissues and peat ................................................................... 67 2.6.6 Section summary....................................................................... 68 2.7 Environmental change in the Welsh uplands ................................... 68 2.8 Conclusions of the literature review ................................................ 74 2.8.1 Research question one: Do differing land use practices affect blanket peatland carbon accumulation in a characteristic manner? ................................................................................ 74 2.8.2 Research question two: Is it appropriate to treat peatland management regimes as