10:45 〜 12:15
[BBC02-P02] Vertical patterns of CH4 emissions from the trunks of four cool-temperate tree species
キーワード：メタン、幹メタン放出、温室効果ガス、森林、葉、冷温帯林
CH4 is a more potent greenhouse gas than the same amount of CO2. It turned out that tree trunks can emit CH4 even in upland forests where the soil is a CH4 sink. Few studies have scaled up CH4 flux from trunks to stand level. However, these studies only measured CH4 flux with one or few chambers below 3 m for scaling up to tree level. This can result in under- or overestimating the flux from trees because the measured part of the trunk is short compared to the total tree height. Therefore, it is necessary to clarify the vertical patterns of the trunk CH4 flux to the upper part of trunks, especially for trees in upland forests where, unlike trees in wetlands, a clear decreasing pattern of flux depending on the height is lacking.
The field investigations were done in the Ashiu Forest Research Station of Kyoto University (35.34 N, 135.76E). The forest is a cool-temperate natural mixed forest with well-drained soil, dominated by Cryptomeria japonica (Japanese cedar). We measured the trunk CH4 fluxes of eight trees of four species at several heights up to 15 m, manipulating a crane truck and using the dynamic closed chamber system connected to a portable trace gas analyzer (Li-7810, Licor, USA). We also measured CH4 flux from shoots including foliage using a transparent bag chamber made of PVC film. The measured trunk CH4 flux was scaled up into tree level by extrapolating the flux using a power function of flux versus height on the trunk.
All trees emitted CH4 at all sampling heights along the trunk, while foliage emitted almost no CH4. We observed similar vertical patterns of trunk emissions in two species (Aesculus turbinata and Fagus crenata) characterized by an increase followed by a decrease with height (range of peak height: 1.8 to 7.5 m above the soil). In the other two species, the vertical pattern in the emission was not consistent between two individuals. One Carpinus turbinata showed increasing emission with trunk height up to 12.4 m above the soil, the position of the highest chamber. Overall, the trunk CH4 emission measured at the base of the trunk (0 to 2.0 m above the soil) was significantly related to the estimated trunk emission at tree level after a logarithm transformation.
Our results showed potential of improving the accuracy of tree-scale CH4 flux estimates, although the vertical patterns of CH4 emissions might somtime differ between species and individuals. The origin of these patterns may be linked to both vertical variations in the CH4 production inside the trunk and to the reduction in trunk diameter with height, increasing the radial diffusion of gases.
The field investigations were done in the Ashiu Forest Research Station of Kyoto University (35.34 N, 135.76E). The forest is a cool-temperate natural mixed forest with well-drained soil, dominated by Cryptomeria japonica (Japanese cedar). We measured the trunk CH4 fluxes of eight trees of four species at several heights up to 15 m, manipulating a crane truck and using the dynamic closed chamber system connected to a portable trace gas analyzer (Li-7810, Licor, USA). We also measured CH4 flux from shoots including foliage using a transparent bag chamber made of PVC film. The measured trunk CH4 flux was scaled up into tree level by extrapolating the flux using a power function of flux versus height on the trunk.
All trees emitted CH4 at all sampling heights along the trunk, while foliage emitted almost no CH4. We observed similar vertical patterns of trunk emissions in two species (Aesculus turbinata and Fagus crenata) characterized by an increase followed by a decrease with height (range of peak height: 1.8 to 7.5 m above the soil). In the other two species, the vertical pattern in the emission was not consistent between two individuals. One Carpinus turbinata showed increasing emission with trunk height up to 12.4 m above the soil, the position of the highest chamber. Overall, the trunk CH4 emission measured at the base of the trunk (0 to 2.0 m above the soil) was significantly related to the estimated trunk emission at tree level after a logarithm transformation.
Our results showed potential of improving the accuracy of tree-scale CH4 flux estimates, although the vertical patterns of CH4 emissions might somtime differ between species and individuals. The origin of these patterns may be linked to both vertical variations in the CH4 production inside the trunk and to the reduction in trunk diameter with height, increasing the radial diffusion of gases.