A Topographic Gradient Drives Spatial Variability of Stem CH4 Fluxes in a Temperate Alder Stand

Autor: Köhn, Daniel; Günther, Anke; Smiljanic, Marko; Jurasinski, Gerald
In:

Ecosystems

ISBN: 1435-0629
DOI: 10.1007/s10021-025-00989-2
Seite: 1 - 15
Jahr: 2025

Einordung:
Institut: Professur Landschaftsökologie und Standortkunde

Abstract:
Tree stems in both wetland and upland forests are a potentially significant source of the greenhouse gas methane (CH4). Stem CH4 emissions are assumed to play an important role on a global scale. Yet, uncertainties regarding temporal and spatial variability as well as transport processes of stem emissions remain high. Here, we assess the spatial variability and range of CH4 egress from 28 black alder (Alnus glutinosa (L.) Gaertn.) trees based on data we recorded during three measurement campaigns in a mature alder carr in spring 2019. Fluxes varied significantly in time and space. The overall temporal variability during the three campaigns was larger than the spatial variability. The fluxes ranged from less than 1 µg m−2 h−1 to 450 µg m−2 h−1 with an average overall flux of 25 ± 59 µg m−2 h−1 (± SD). Stem CH4 fluxes were highest (61.6 ± 104.5 µg m−2 h−1) during higher soil temperatures in spring, with increasing sap flux density and an intermediate water level just above the surface (+ 2.7 ± 0.3 cm). Morphological properties of the trees, including diameter at breast height, their position on hummocks or hollows and height of the measurement on the stem, largely failed to explain variability in stem CH4 fluxes. Large-scale topography (overall elevation gradient) within the study site and CO2 flux were the best predictors of stem CH4 emissions, but inundation and leaf out also significantly influenced stem CH4 fluxes. Thus, large-scale factors such as topography as an indirect indicator for water level can potentially facilitate upscaling of tree stem CH4 emissions.

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