Tropical wetlands are not included in Earth system models, despite being an important source of methane (CH4) and contributing a large fraction of carbon dioxide (CO2) emissions from land use, land use change, and forestry in the tropics. This review identifies a remarkable lack of data on the carbon balance and gas fluxes from undisturbed tropical wetlands, which limits the ability of global change models to make accurate predictions about future climate. We show that the available data on in situ carbon gas fluxes in undisturbed forested tropical wetlands indicate marked spatial and temporal variability in CO2 and CH4 emissions, with exceptionally large fluxes in Southeast Asia and the Neotropics. By upscaling short-term measurements, we calculate that approximately 90 ± 77 Tg CH4 year−1 and 4540 ± 1480 Tg CO2 year−1 are released from tropical wetlands globally. CH4 fluxes are greater from mineral than organic soils, whereas CO2 fluxes do not differ between soil types. The high CO2 and CH4 emissions are mirrored by high rates of net primary productivity and litter decay. Net ecosystem productivity was estimated to be greater in peat-forming wetlands than on mineral soils, but the available data are insufficient to construct reliable carbon balances or estimate gas fluxes at regional scales. We conclude that there is an urgent need for systematic data on carbon dynamics in tropical wetlands to provide a robust understanding of how they differ from well-studied northern wetlands and allow incorporation of tropical wetlands into global climate change models.

Pristine tropical peat swamp forests (PSFs) represent a unique wetland ecosystem of distinctive hydrology which support unique biodiversity and globally significant stores of soil carbon. Yet in Indonesia and Malaysia, home to 56% of the world's tropical peatland, they are subject to considerable developmental pressures, including widespread drainage to support agricultural needs. In this article, we review the ecology behind the functioning and ecosystem services provided by PSFs, with a particular focus on hydrological processes as well as the role of the forest itself in maintaining those services. Drawing on this, we review the suitability of current policy frameworks and consider the efficacy of their implementation. We suggest that policies in Malaysia and Indonesia are often based around the narrative of oil palm and other major monocrops as drivers of prosperity and development. However, we also argue that this narrative is also being supported by a priori claims concerning the possibility of sustainability of peat swamp exploitation via drainage-based agriculture through the adherence to best management practices. We discuss how this limits their efficacy, uptake and the political will towards enforcement. Further, we consider how both narratives (prosperity and sustainability) clearly exclude important considerations concerning the ecosystem value of tropical PSFs which are dependent on their unimpacted hydrology. Current research clearly shows that the actual debate should be focused not on how to develop drainage-based plantations sustainably, but on whether the sustainable conversion to drainage-based systems is possible at all.

(2017) Impacts of conversion of tropical peat swamp forest to oil palm plantation on peat organic chemistry, physical properties and carbon stocks. Geoderma, 289 . pp. 36-45. ISSN 1872-6259 Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/43906/1/Tonks%20et%20al.%20for %20Geoderma_18%20Oct.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the Creative Commons Attribution Non-commercial No Derivatives licence and may be reused according to the conditions of the licence. For more details see: http://creativecommons.org/licenses/by-nc-nd/2.5/ A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk greater than decomposition rates (Jauhiainen et al., 2008). 54These unique systems are valuable resources, contributing a multitude of ecosystem services. 55Above ground, tropical rainforests maintain areas of high biodiversity by providing habitats 56 for a variety of species, many of which are endemic (Posa et al. 2011; Keddy et al., 2009). 57Below ground, the sequestration of atmospheric carbon is interwoven into the fabric of the 58 ecosystem (Jauhiainen et al., 2008). An estimated 42,000 megatons of ancient carbon is 59 stored in 12% of the total land area of Southeast Asia alone, making this one of the largest 60 stores of terrestrial carbon on Earth (Wetlands International, 2014). Peat soil structure is 61 responsible for ecosystem processes by controlling hydrology, which regulates hydrological 62 features within the catchment. For example, its high organic matter content and low bulk 63 density allows peat to acts as a water reservoir, mitigating extreme conditions such as floods 64 and droughts (Huat et al., 2011;Wösten et al., 2008). 65Land use change over the past century has been a key driver of peatland degradation, with 66 conversion to agriculture and forestry, and peat extraction sites, leading to artificially lowered 67 water tables (Haddaway et al., 2014 (Hooijer et al., 2010; Couwenberg et al., 2010). 85A greater degree of peat decomposition results in loss of structure as fresh litter is first broken 86 down to fibrous hemic peat, and then, following sustained decomposition, to sapric peat 87 (Wüst et al., 2003). The progressing decomposition process alters the organic components 88 and chemistry due to loss of carbon and conversion of readily decomposable materials, such 89 as polysaccharides, celluloses and hemicelluloses, with only more recalcitrant compounds 90 such as lignin and humic substances remaining (Andriesse, 1988; Broder et al., 2012; Kuhry 91 and Vitt, 1996;...