Methane production and emissions in trees and forests.

Contents Summary 35 I. Introduction 36 II. Tree CH fluxes 36 III. Tree emissions of soil-produced CH 40 IV. Tree-produced CH 42 V. Trees in forest CH budgets 44 VI. Conclusions 46 Acknowledgements 48 Author contributions 48 References 48 SUMMARY: Forest ecosystem methane (CH ) research has focused on soils, but trees are also important sources and sinks in forest CH budgets. Living and dead trees transport and emit CH produced in soils; living trees and dead wood emit CH produced inside trees by microorganisms; and trees produce CH through an abiotic photochemical process. Here, we review the state of the science on the production, consumption, transport, and emission of CH 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 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 , microbial processes produce and oxidize CH inside trees, a lack of mechanistic models, the diffuse nature of forest CH fluxes, complex overlap between sources and sinks, and extreme variation across individuals. Understanding the complex processes that regulate CH 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.