9:30 AM - 9:45 AM
[BCG05-02] The effects of bark stripping by bears on CH4 emissions from Cryptomeria japonica trunks
Keywords:Methane, Forest, Greenhouse gas, Flux, Carbon cycling, Soil
CH4 is one of the most important greenhouse gases, along with CO2. Forest ecosystems were considered methane sinks because forest soils consume atmospheric CH4. However, CH4 produced by microbes in the deep soil and tree trunks has been shown to be emitted into the atmosphere through tree trunks. Moisan et al. (2024) has shown that CH4 emissions from gymnosperms like Cryptomeria japonica (Sugi) were much lower than those from other species. Nevertheless, C. japonica trunks can serve as habitats for methane-producing archaea (Harada et al. 2024), and the potential CH4 production capacities of their trunks were comparable to those of other species (Epron et al. 2022). Additionally, some studies on other species have suggested that wounds on tree trunks can be overlooked as CH4 sources(Gorgolewski et al. 2022; Jeffrey et al. 2021), which may also apply to C. japonica. Therefore, we expected that C. japonica trunks with bark-stripped by bears would emit significant amounts of CH4. Unlike previous studies focusing on healthy trees, we specifically examined C. japonica trunks with bark-stripped by bears.
The field investigations were conducted in the Ashiu Experimental Forest of Kyoto University in the northeastern part of Kyoto Prefecture. The forest is a cool temperate forest with well-drained soils, dominated by C. japonica. We measured the CH4 fluxes from bark-stripped and unstripped C. japonica trunks and soils using a dynamic closed chamber system connected to a portable trace gas analyzer (Li-7810, Licor, USA). The measured trunk CH4 fluxes were scaled up to tree level and stand level, and the measured soil CH4 fluxes were scaled up to stand level. We also evaluated the internal status of each subject tree by acoustic tomography using ArborSonic (Fakopp Enterprise Bt., Agfalva, Hungary) and the relative wood density Resistograph (IML-RESI F-Series, IML, Germany) to detect decays in trunks.
CH4 fluxes from bark-unstripped C. japonica trunks were close to zero, while fluxes from bark-stripped C. japonica were always positive and exceeded at most 190 nmol m-2 s-1. This value was two orders of magnitude higher than other measurements conducted previously at the same study site (Epron et al. 2022; Epron & Mochidome 2024; Mochidome & Epron 2024). At stand level, CH4 emissions from C. japonica trunks offset soil CH4 consumption by approximately 17 %. Inter-individual variability in CH4 emissions from bark-stripped C. japonica trunks was explained by variations in DBH (diameter at breast height) between trees. Moreover, even within the same individuals, CH4 fluxes from bark-stripped trunks differed by 10 to 380 times. These variations in CH4 emissions can be attributed to differences in CH4 diffusivity, production, and consumption by methane-oxidizing bacteria living in bark and trunks. These factors influencing CH4 emissions may be affected by wood decay caused by bark stripping by bears.
This study contributes to the understanding of CH4 emission from tree trunks and deepens our knowledge of greenhouse gas dynamics in forest ecosystems. By elucidating the impact of bark stripping on CH4 emissions, this research provides new insights that can improve the accuracy of forest CH4 budget estimates.
The field investigations were conducted in the Ashiu Experimental Forest of Kyoto University in the northeastern part of Kyoto Prefecture. The forest is a cool temperate forest with well-drained soils, dominated by C. japonica. We measured the CH4 fluxes from bark-stripped and unstripped C. japonica trunks and soils using a dynamic closed chamber system connected to a portable trace gas analyzer (Li-7810, Licor, USA). The measured trunk CH4 fluxes were scaled up to tree level and stand level, and the measured soil CH4 fluxes were scaled up to stand level. We also evaluated the internal status of each subject tree by acoustic tomography using ArborSonic (Fakopp Enterprise Bt., Agfalva, Hungary) and the relative wood density Resistograph (IML-RESI F-Series, IML, Germany) to detect decays in trunks.
CH4 fluxes from bark-unstripped C. japonica trunks were close to zero, while fluxes from bark-stripped C. japonica were always positive and exceeded at most 190 nmol m-2 s-1. This value was two orders of magnitude higher than other measurements conducted previously at the same study site (Epron et al. 2022; Epron & Mochidome 2024; Mochidome & Epron 2024). At stand level, CH4 emissions from C. japonica trunks offset soil CH4 consumption by approximately 17 %. Inter-individual variability in CH4 emissions from bark-stripped C. japonica trunks was explained by variations in DBH (diameter at breast height) between trees. Moreover, even within the same individuals, CH4 fluxes from bark-stripped trunks differed by 10 to 380 times. These variations in CH4 emissions can be attributed to differences in CH4 diffusivity, production, and consumption by methane-oxidizing bacteria living in bark and trunks. These factors influencing CH4 emissions may be affected by wood decay caused by bark stripping by bears.
This study contributes to the understanding of CH4 emission from tree trunks and deepens our knowledge of greenhouse gas dynamics in forest ecosystems. By elucidating the impact of bark stripping on CH4 emissions, this research provides new insights that can improve the accuracy of forest CH4 budget estimates.