European beech is a net annual source of methane (CH4)

Trees are known to be sources of methane (CH₄), an important greenhouse gas, into the atmosphere. However, still little is known about the seasonality of the tree stem CH₄ fluxes, particularly for the dormant season, and about the impact of environmental parameters on this gas exchange. This makes the estimation of net annual ecosystem CH₄ fluxes difficult.

We determined seasonal dynamics of CH₄ exchange of mature European beech stems (Fagus sylvatica) and of adjacent forest floor in a temperate montane forest of White Carpathians, Czech Republic, from November 2017 to December 2018. We used static chamber methods and gas chromatographic analyses. We aimed to understand the unknown role in seasonal changes of CH₄ fluxes of these forests, and the spatiotemporal variability of the tree fluxes.

The beech stems were net annual sources for atmospheric CH₄, whereas the forest floor was a predominant sink for CH₄. The stem CH₄ emissions showed high inter-individual variability and clear seasonality following the stem CO₂ efflux. The fluxes of CH₄ peaked during the vegetation season, and remained low but significant to the annual totals during winter dormancy. By contrast, the forest floor CH₄ uptake followed an opposite flux trend with low CH₄ uptake detected in the winter dormant season and elevated CH₄ uptake during the vegetation season. Based on our preliminary analyses, the detected high spatial variability in stem CH₄ emissions can be explained neither by the CH₄ exchange at the forest floor level, nor by soil CH₄ concentrations, soil water content and soil temperature, all measured in vertical soil profiles close to the studied trees.

European beech trees, native and widely spread species of Central Europe, seem to markedly contribute to the seasonal dynamics of the ecosystem CH₄ exchange, and their CH₄ fluxes should be included into forest greenhouse gas emission inventories.

 

Acknowledgement

This research was supported by the Czech Science Foundation (17-18112Y), National Programme for Sustainability I (LO1415), CzeCOS (LM2015061), and SustES - Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797). We thank Libor Borák and Leszek Dariusz Laptaszyński for their technical and field support.