Online Resource 3 to Table 3
This table is a summary of all previously published field studies of stem CH4 emissions. Some studies included cover extensive time periods. To make data more comparable to ours, when possible, only a subset representing the growing season were included in mean and range estimates. For example, in Pangala et al. (2015) values from only June- October were used, however, in Warner et al. (2017) all values were used.
Terazawa et al. (2007): Values for the range at each chamber height were extracted from Figure 1a using WebPlotDigitizer(Rohatgi 2017). Range estimates represent the minimum and maximum sampling round means from five trees, not a high or low measurement from a single tree stem. The values for the mean (n=5) at each height were taken directly from the text.
Gauci et al. (2010): Values for the range were taken directly from Table 1. The mean (n=9) and standard deviation was calculated using values from Table 1.
Covey et al. (2012): This study is unique within this table because stem CH4 fluxes were modeled and estimated from measurements of CH4 concentration within the tree stem. The original units were based on stem volume and biomass. Used a factor of 0.007316 m3 of wood per m2 of forest to convert to flux per unit area per time. This factor was derived from the paper.
Pangala et al. (2013): Range estimates were obtained using values extracted from Figure 4b with WebPlotDigitizer. The mean (n=32) and standard deviation were calculated using the same set of values.
Pangala et al. (2015): Range estimates were obtained using values extracted from Figure 1 using WebPlotDigitizer and separated by species. This study included measurements from April 2011 to April 2012. To more accurately reflect growing season mean fluxes only measurements from June thru October 2011 were included in the calculations.
Terazawa et al. (2015): Values for the range estimate were taken directly from the text. Mean value was estimated using values extracted from Figures 4a and 4e with WebPlotDigitizer. All data points from the two figures were included in the mean (n=30) and standard deviation.
Wang et al. (2016): Values for the range and mean were taken directly from the text. No standard deviation was available.
Machacova et al. (2016): No range estimates were available. The value for the median was taken directly from the text. No standard deviation was available. The authors of this study also measured shoot fluxes but those values were not included in this table. It may be of note that each stem chamber measurement was made over a six hour period, which is longer than other studies cited here.
Warner et al. (2017): The original stem CH4 flux units for this study were nmol m-2 s-1. Only maximum, mean and standard deviation were provided in the text.
Maier et al. (2017): The original stem CH4 flux units for this study were nmol m-2 s-1. Values for the range and mean were taken directly from the text. Two sites were studied but measureable stem CH4 fluxes were only observed at one of the sites (Stitna). This table only shows data from the Stitna site.