Methane production and emissions in trees and forests

Abstract

Forest ecosystem methane (CH 4 ) research has focused on soils, but trees are also important sources and sinks in forest CH 4 budgets. Living and dead trees transport and emit CH 4 produced in soils; living trees and dead wood emit CH 4 produced inside trees by microorganisms; and trees produce CH 4 through an abiotic photochemical process. Here, we review the state of the science on the production, consumption, transport, and emission of CH 4 by living and dead trees, and the spatial and temporal dynamics of these processes across hydrologic gradients inclusive of wetland and upland ecosystems. Emerging research demonstrates that tree CH 4 emissions can significantly increase the source strength of wetland forests, and modestly decrease the sink strength of upland forests. Scaling from stem or leaf measurements to trees or forests is limited by knowledge of the mechanisms by which trees transport soil-produced CH 4 , microbial processes produce and oxidize CH 4 inside trees, a lack of mechanistic models, the diffuse nature of forest CH 4 fluxes, complex overlap between sources and sinks, and extreme variation across individuals. Understanding the complex processes that regulate CH 4 source-sink dynamics in trees and forests requires cross-disciplinary research and new conceptual models that transcend the traditional binary classification of wetland vs upland forest.

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

“…It is challenging to directly compare our CH 4 fluxes to other studies, as most previous work has only measured fluxes at one or two height increments and/or at different heights, seasons, species, freshwater systems and using different methods. To simplify, we compared our average flux rates from ≤ 40 cm of the arid‐tropical dead mangrove stems (714.5 ± 127.2 μmol m −2 d −1 ), to lowland studies measured from similar stem heights (15–50 cm) as summarized in Covey & Megonigal (). We found our dead tree stem CH 4 fluxes (from ≤ 40 cm) were c .…”

“…Comparison of average dead and living mangrove tree stem methane (CH 4 ) fluxes (our study, Eqn 3) to the range of current literature of wetland tree stem CH 4 fluxes (grey bars) extracted from table 1 in Covey & Megonigal (). Note: height measurements and scaling approaches vary amongst studies.…”

Impact of forest plantation on methane emissions from tropical peatland

“…In tropical peatlands, the majority of root biomass occurs within the upper 50 cm of the peat column (Brady, 1997;Sulistiyanto, 2004), and dissolved CH 4 in the root zone can be significant (100-1,500 µmol/L; Hoyt, 2017;Pangala et al, 2013). The magnitude of vegetation-mediated transport seems to be directly regulated by a well-connected root-stem pathway for the CH 4 transport, although it is strongly (if not primarily) controlled by the availability of dissolved CH 4 in the root zone (Covey & Megonigal, 2019;Pangala et al, 2013Pangala et al, , 2017Waddington, Roulet, & Swanson, 1996). At the natural forest site, S. uliginosa, C. ferrugineum, and Syzygium spp.…”

Longitudinal Gradients in Tree Stem Greenhouse Gas Concentrations Across Six Pacific Northwest Coastal Forests

“…Greenhouse gas (GHG) emissions from herbaceous plants have been extensively studied in wetlands (Frenzel & Rudolph, 1998;Laanbroek, 2009;Nisbet et al, 2009;Nouchi et al, 1990;Yu et al, 1997), and tree stems have long been known to contain elevated concentrations of GHGs, particularly carbon dioxide (CO 2 ; Bushong, 1907). However, it is only in recent years that emissions of major GHGs beyond CO 2 -that is, methane (CH 4 ) and nitrous oxide (N 2 O)-from tree stems have been recognized as a potentially significant component of global GHG budgets (Carmichael et al, 2014;Covey & Megonigal, 2019;Pangala et al, 2013;Pangala et al, 2015;Rice et al, 2010). The omission of GHG fluxes from trees may overestimate the sink potential (Pitz & Megonigal, 2017) and underestimate the release (Covey et al, 2012;Wang et al, 2016) of GHGs from upland and wetland forests, respectively.…”