Methane emissions from tree stems: a new frontier in the global carbon cycle

Barba, Josep; Bradford, Mark A.; Brewer, Paul E.; Bruhn, Dan; Covey, Kristofer; Haren, Joost van; Megonigal, J. Patrick; Mikkelsen, Teis Nørgaard; Pangala, Sunitha Rao; Pihlatie, Mari; Poulter, Benjamin; Rivas‐Ubach, Albert; Schadt, Christopher W.; Terazawa, Kazuhiko; Warner, Daniel L.; Zhang, Zhen; Vargas, Rodrigo

doi:10.1111/nph.15582

Cited by 131 publications

(157 citation statements)

References 76 publications

(150 reference statements)

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“…CH 4 fluxes exhibit finescale spatial variability that can span orders of magnitude within a landscape (Peltola et al 2015;Marushchak et al 2016;Desai et al 2015;Treat et al 2018a;Iwata et al 2018), attributable to heterogeneous soil properties and moisture conditions, vegetation composition, and land use (Davidson et al 2016;Parmentier et al 2011;Chamberlain et al 2018). Furthermore, there is evidence that traditionally unmeasured surfaces (i.e., tree stems) are important sources of CH 4 to the atmosphere and could explain spatial heterogeneity within ecosystems (Barba et al 2019). Accurately representing spatial heterogeneity and the relative fraction of uplands and wetlands is imperative for interpreting and predicting CH 4 emissions within many ecosystems, and for upscaling flux measurements regionally and globally as wetlands are hot spots for carbon cycling (Treat et al 2018a;Tuovinen et al 2019;Rößger et al 2019).…”

Section: Ec Flux Data Quality Assessmentmentioning

confidence: 99%

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

Knox¹,

Jackson²,

Poulter

et al. 2019

Bulletin of the American Meteorological Society

143

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This paper describes the formation of, and initial results for, a new FLUXNET coordination network for ecosystem-scale methane (CH4) measurements at 60 sites globally, organized by the Global Carbon Project in partnership with other initiatives and regional flux tower networks. The objectives of the effort are presented along with an overview of the coverage of eddy covariance (EC) CH4 flux measurements globally, initial results comparing CH4 fluxes across the sites, and future research directions and needs. Annual estimates of net CH4 fluxes across sites ranged from −0.2 ± 0.02 g C m–2 yr–1 for an upland forest site to 114.9 ± 13.4 g C m–2 yr–1 for an estuarine freshwater marsh, with fluxes exceeding 40 g C m–2 yr–1 at multiple sites. Average annual soil and air temperatures were found to be the strongest predictor of annual CH4 flux across wetland sites globally. Water table position was positively correlated with annual CH4 emissions, although only for wetland sites that were not consistently inundated throughout the year. The ratio of annual CH4 fluxes to ecosystem respiration increased significantly with mean site temperature. Uncertainties in annual CH4 estimates due to gap-filling and random errors were on average ±1.6 g C m–2 yr–1 at 95% confidence, with the relative error decreasing exponentially with increasing flux magnitude across sites. Through the analysis and synthesis of a growing EC CH4 flux database, the controls on ecosystem CH4 fluxes can be better understood, used to inform and validate Earth system models, and reconcile differences between land surface model- and atmospheric-based estimates of CH4 emissions.

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Section: Ec Flux Data Quality Assessmentmentioning

confidence: 99%

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

Knox¹,

Jackson²,

Poulter

et al. 2019

Bulletin of the American Meteorological Society

143

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“…Only recently have tree stem CH 4 emissions been investigated as an important source of CH 4 to the atmosphere (Terazawa et al, 2007;Covey et al, 2012;Pangala et al, 2015). Tree stem CH 4 emissions have been found to account for up to 50% of the Amazon basin CH 4 budget (Pangala et al, 2017), and characterizing and quantifying tree stem CH 4 fluxes is now recognized as 'a new frontier in the global carbon cycle' (Barba et al, 2019a).…”

Section: Introductionmentioning

confidence: 99%

“…Recent reviews of tree-mediated CH 4 emissions rely upon data synthesized from mostly living trees of freshwater wetlands, floodplains and upland forested origins (Barba et al, 2019a;Covey & Megonigal, 2019). To date, very few studies have assessed CH 4 fluxes from standing dead tree stems (Carmichael et al, 2014;Warner et al, 2017) and/or saline wetlands.…”

Section: Introductionmentioning

confidence: 99%

“…To date, very few studies have assessed CH 4 fluxes from standing dead tree stems (Carmichael et al, 2014;Warner et al, 2017) and/or saline wetlands. Furthermore, there is no consensus for the biophysical mechanisms transporting CH 4 along the soil-tree-atmosphere continuum (Barba et al, 2019a), with debate continuing as to whether trees: act as passive pipes (diffusion) connecting the rhizosphere to the atmosphere; participate as active pipes (via xylem flow); or produce CH 4 internally in the heartwood (Covey et al, 2012;Barba et al, 2019b). Tree species, tree size, ecological adaptations, seasonality and hydrogeophysical context all likely play a role in the production and pathways of tree stem CH 4 flux (Keppler et al, 2006;McLeod et al, 2008;Pangala et al, 2017;Pitz et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Are methane emissions from mangrove stems a cryptic carbon loss pathway? Insights from a catastrophic forest mortality

et al. 2019

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Summary Growing evidence indicates that tree‐stem methane (CH4) emissions may be an important and unaccounted‐for component of local, regional and global carbon (C) budgets. Studies to date have focused on upland and freshwater swamp‐forests; however, no data on tree‐stem fluxes from estuarine species currently exist. Here we provide the first‐ever mangrove tree‐stem CH4 flux measurements from >50 trees (n = 230 measurements), in both standing dead and living forest, from a region suffering a recent large‐scale climate‐driven dieback event (Gulf of Carpentaria, Australia). Average CH4 emissions from standing dead mangrove tree‐stems was 249.2 ± 41.0 μmol m−2 d−1 and was eight‐fold higher than from living mangrove tree‐stems (37.5 ± 5.8 μmol m−2 d−1). The average CH4 flux from tree‐stem bases (c. 10 cm aboveground) was 1071.1 ± 210.4 and 96.8 ± 27.7 μmol m−2 d−1 from dead and living stands respectively. Sediment CH4 fluxes and redox potentials did not differ significantly between living and dead stands. Our results suggest both dead and living tree‐stems act as CH4 conduits to the atmosphere, bypassing potential sedimentary oxidation processes. Although large uncertainties exist when upscaling data from small‐scale temporal measurements, we estimated that dead mangrove tree‐stem emissions may account for c. 26% of the net ecosystem CH4 flux.

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“…Several important processes may be missing from wetland models: (i) The production and transport of CH 4 by trees has recently been observed in forested systems in temperate and tropical biomes (Barba et al, 2019;Covey & Megonigal, 2019;Welch et al, 2019). In the tropics, for example, transport of CH 4 via tree stems accounts for a large part of the overall CH 4 budget (Pangala et al, 2017).…”

Section: Wetlands and Other Natural Water Bodiesmentioning

confidence: 99%

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

Ganesan

Schwietzke²,

Poulter

et al. 2019

Global Biogeochemical Cycles

102

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The 2015 Paris Agreement of the United Nations Framework Convention on Climate Change aims to keep global average temperature increases well below 2 °C of preindustrial levels in the Year 2100. Vital to its success is achieving a decrease in the abundance of atmospheric methane (CH4), the second most important anthropogenic greenhouse gas. If this reduction is to be achieved, individual nations must make and meet reduction goals in their nationally determined contributions, with regular and independently verifiable global stock taking. Targets for the Paris Agreement have been set, and now the capability must follow to determine whether CH4 reductions are actually occurring. At present, however, there are significant limitations in the ability of scientists to quantify CH4 emissions accurately at global and national scales and to diagnose what mechanisms have altered trends in atmospheric mole fractions in the past decades. For example, in 2007, mole fractions suddenly started rising globally after a decade of almost no growth. More than a decade later, scientists are still debating the mechanisms behind this increase. This study reviews the main approaches and limitations in our current capability to diagnose the drivers of changes in atmospheric CH4 and, crucially, proposes ways to improve this capability in the coming decade. Recommendations include the following: (i) improvements to process‐based models of the main sectors of CH4 emissions—proposed developments call for the expansion of tropical wetland flux measurements, bridging remote sensing products for improved measurement of wetland area and dynamics, expanding measurements of fossil fuel emissions at the facility and regional levels, expanding country‐specific data on the composition of waste sent to landfill and the types of wastewater treatment systems implemented, characterizing and representing temporal profiles of crop growing seasons, implementing parameters related to ruminant emissions such as animal feed, and improving the detection of small fires associated with agriculture and deforestation; (ii) improvements to measurements of CH4 mole fraction and its isotopic variations—developments include greater vertical profiling at background sites, expanding networks of dense urban measurements with a greater focus on relatively poor countries, improving the precision of isotopic ratio measurements of 13CH4, CH3D, 14CH4, and clumped isotopes, creating isotopic reference materials for international‐scale development, and expanding spatial and temporal characterization of isotopic source signatures; and (iii) improvements to inverse modeling systems to derive emissions from atmospheric measurements—advances are proposed in the areas of hydroxyl radical quantification, in systematic uncertainty quantification through validation of chemical transport models, in the use of source tracers for estimating sector‐level emissions, and in the development of time and space resolved national inventories. These and other recommendations are proposed for...

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Methane emissions from tree stems: a new frontier in the global carbon cycle

Cited by 131 publications

References 76 publications

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

Are methane emissions from mangrove stems a cryptic carbon loss pathway? Insights from a catastrophic forest mortality

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

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