DOI: 10.5061/dryad.z34tmpgm4
title: Data from: Drivers of intra-individual spatial variability in methane emissions from tree trunks in upland forest

description: CH4 emissions from tree trunks in upland forests should be scaled
 accurately in order to assess the role of tree trunks in the forest
 CH4 budget. As the chambers used to measure emissions cover only
 a small part of the tree trunks, it is necessary to understand the
 intra-individual spatial variability in trunk CH4 emissions. We
 measured trunk CH4 flux at nine locations per individual on four
 trees in a cool-temperate upland forest. To appreciate the origin of this
 variability and the underlying processes, we also measured the potential
 rate of CH4 production and CH4 concentration at sapwood and characterized
 wood and bark. Up to 15-fold spatial variation in CH4 fluxes were
 observed at the individual level. This variability can be highlighted by
 the variation in the sapwood CH4 concentration which was further
 explained by the variation in CH4 production rate. The radial
 CH4 diffusivity calculated from concentration gradients and
 emissions was not related to the measured characteristics of either wood
 or bark, raising the question of the diffusion pathway. We emphasized the
 importance of sampling trunk CH4 flux at multiple locations on
 the surface of a tree trunk to capture spatial variability, a prerequisite
 for estimating tree-level CH4 emissions.
description: Trunk CH<sub>4</sub> flux was measured using a
 cavity-enhanced absorption spectroscopy gas analyzer (Li-7810, Licor,
 Lincoln, USA), from the trunk surface area of 127 cm2 on average, with a
 volume of a measuring system including a chamber, tubes, and an analyzer
 of 2509 cm3. Changes in the CH<sub>4</sub> and
 CO<sub>2</sub> concentrations in the stem chamber were
 recorded for 4 min at a frequency of 1 Hz. After
 finishing all trunk CH<sub>4</sub> flux measurements, chambers
 were removed, and the wood at these chamber locations was bored with an
 increment borer (5.15 mm internal diameter, Haglof Sweden) to a depth of
 20 cm. After the removal of the wood core, the hole left by the borer was
 enlarged using a driller to a diameter of 10 mm. A stainless-steel tube
 (10 mm outer diameter, 12 cm length) was inserted into the hole to a depth
 of 10 cm. The tube was flushed with pure N<sub>2</sub> to
 expel as much O<sub>2</sub> as possible, then the open end of
 the tube was capped with a rubber septum (Asone, Butyl W Plug, Osaka,
 Japan). As the inner 10 cm part of the hole was not covered with the
 stainless tube, gases inside the trunk can diffuse into the tubing system
 and reach an equilibrium. One week later, 0.1 mL of the gas inside the
 tube was sampled with a syringe penetrating the septum and immediately
 measured by gas analyzer (Li-7810) with a small volume sample kit (Li
 7810-110). Wood cores were extracted from the trunk
 with an increment borer and the innermost 7 cm core was incubated using a
 mixture (N<sub>2</sub>, 10% CO<sub>2</sub> and 1%
 H<sub>2</sub>) at 25 °C in a dark incubator for one week. An
 air sample (10 μl) was then drawn from each vial through the septum into a
 syringe and injected through the septum of the small volume sample kit (Li
 7800-110) connected to the gas analyser. The ex-situ
 CH<sub>4</sub> production rate was calculated by dividing the
 increase in CH<sub>4</sub> concentration by the duration of
 the incubation and the dry mass of the wood segment, accounting for the
 volume of the tube corrected for the volume of the segment.
description: # Drivers of intra-individual spatial variability in methane emissions
 from tree trunks in upland forest
 [https://doi.org/10.5061/dryad.z34tmpgm4](https://doi.org/10.5061/dryad.z34tmpgm4) ## Description of methods Trunk CH4 flux was measured using a cavity-enhanced absorption spectroscopy gas analyzer (Li-7810, Licor, Lincoln, USA), from the trunk surface area of 127 cm2 on average, with a volume of a measuring system including a chamber, tubes, and an analyzer of 2509 cm3. Changes in the CH4 and CO2 concentrations in the stem chamber were recorded for 4 min at a frequency of 1 Hz. After finishing all trunk CH4 flux measurements, chambers were removed, and the wood at these chamber locations was bored with an increment borer (5.15 mm internal diameter, Haglof Sweden) to a depth of 20 cm. After the removal of the wood core, the hole left by the borer was enlarged using a driller to a diameter of 10 mm. A stainless-steel tube (10 mm outer diameter, 12 cm length) was inserted into the hole to a depth of 10 cm. The tube was flushed with pure N2 to expel as much O2 as possible, then the open end of the tube was capped with a rubber septum (Asone, Butyl W Plug, Osaka, Japan). As the inner 10 cm part of the hole was not covered with the stainless tube, gases inside the trunk can diffuse into the tubing system and reach an equilibrium. One week later, 0.1 mL of the gas inside the tube was sampled with a syringe penetrating the septum and immediately measured by gas analyzer (Li-7810) with a small volume sample kit (Li 7810-110). Wood cores were extracted from the trunk with an increment borer and the innermost 7 cm core was incubated using a mixture (N2, 10% CO2 and 1% H2) at 25 °C in a dark incubator for one week. An air sample (10 μl) was then drawn from each vial through the septum into a syringe and injected through the septum of the small volume sample kit (Li 7800-110) connected to the gas analyser. The ex-situ CH4 production rate was calculated by dividing the increase in CH4 concentration by the duration of the incubation and the dry mass of the wood segment, accounting for the volume of the tube corrected for the volume of the segment. ## Description of each column of the table The 2nd row indicates the unit for each quantity. * **Tree**: Tree id consist of species id + individual number. At stands for Aesculus turbinata. Three tree (#1 to #3) were used from this specie. Fc stands for Fagus crenata. One tree (#1) was used. * **DBH**: Diameter at breast height in cm. * **Chamber**: Alphabetical ID. * **Azimuth**: Azimuth from the North seen from the center of the trunk, where the measuring locations (chamber) exists. * **Height**: Chamber height above the ground (soil) in cm. * **FCH4_SM**: Seasonal mean value (from mid-May to October) of trunk CH4 flux. The unit is nmolCH4 m-2 s-1. * **FCH4_OCT**: Single value of trunk CH4 flux measured in October. Each of one chamber per individual was removed before the measurement in October, so in total 4 cells are blank. The unit is nmolCH4 m-2 s-1. * **CH4conc_sw**: CH4 concentration in sapwood of each measuring locations, expressed in ppm. Each of one chamber per individual was not measured. CH4 concentration at “E” chamber location of At#3 was not able to be measured because the stainless steel tube was filled with water which was coming out from the trunk. * **CH4ProductionRate**: ex-situ CH4 production rate of wood core sampled from inner sapwood (15 to 20 cm deep from the bark). The production rate is per 1 g of dry wood and per 1 hour. * **Diffusivity**: Radial diffusibity of wood for CH4. See ‘materials and method’ section of the main body. * **MC_inner**: Dry-base moisture content of inner sapwood where CH4 production rate was quantified. * **BD_inner**: Bulk density of inner sapwood. * **MC_outer**: Dry-base moisture content of outer sapwood where radial CH4 diffusion from the inner sapwood to the trunk surface should occur. * **BD_outer**: Bulk density of outer sapwood where radial CH4 diffusion from the inner sapwood to the trunk surface should occur. * **MC_bark**: Dry-base moisture content of bark. * **BD_bark**: Bulk density of bark. * **BarkThickness**: Bark thickness in cm.