Variation in Methane Emissions from Tree Stems in Upland and Seasonally Flooded Forests in the Amazon Basin

Authors

Joost van Haren¹* (jvanhare@arizona.edu), Jose-Mauro de Moura², Raphael Tapajos², Miércio Ferreira Jr.², Taiane Alves², Rodrigo da Silva², Cosme de Oliveira Jr.³, Laëtitia Bréchet¹, Scott Saleska¹

Institutions

¹University of Arizona, Tucson, AZ; ²Federal University of Western Pará, Santarém, Pará, Brazil; ³Brazilian Agricultural Research Corporation (Embrapa), Santarém, Pará, Brazil

Abstract

Methane emissions of tree stems have been gathering much attention (Pangala et al. 2017; Barba et al. 2019); however, in seasonally flooded (várzea) forests along the Amazon river, researchers have only scant measurements of the dynamics of stem emissions. The team is developing seasonal ecosystem and component methane flux measurements in both a várzea and an upland forest near Santarém, Brazil. The team will present preliminary eddy covariance and monthly tree and soil flux results from the upland tower site and stem flux measurements from specific tree stems in the seasonally flooded sites. These initial measurements have been made as part of the measurement systems’ development and testing and the várzea forest site selection process. All fluxes will be analyzed using gasfluxes R package, which the team modified to work R scripts for flux measurement data gathering methods.

Methane stem fluxes in the upland site appear to be higher in tree species with lower wood density and higher sap flux rates. Seasonal variability of stem fluxes in the upland forest is very small, suggesting that the source methane variability is much lower than in the várzea forests. Várzea tree stem fluxes are several orders of magnitude higher in the wet (flooded) season relative to the dry season and the upland forest site. Tree stem flux measurements along vertical profiles show an exponential decay of methane emissions with height, suggesting that most methane is emitted within the first 2 m of height along the stem. Cylindrical diffusion of methane flux along tree stems best fits the measured flux data from the várzea forest sites.

References

Barba, J., et al. 2019. “Methane Emissions from Tree Stems: A New Frontier in the Global Carbon Cycle,” New Phytologist 222(1), 18–28. DOI:10.1111/nph.15582.

Pangala, S. R., et al. 2017. “Large Emissions from Floodplain Trees Close the Amazon Methane Budget,” Nature 552, 230–34. DOI:10.1038/nature24639.