Trees Absorb Methane, Too? What Will Fractivists Do Now?

When it became clear CO2 was not the big bugaboo the anti-fossil fuels crowd thought it was and that natural gas produced less of the stuff than other fossil fuels anyway, the NGO-subsidized Cornell University gang of fractivists shifted their emphasis to methane. They said methane (CH4) was far worse than CO2 and started developing scare theories along that line.

This was useful for their cause because few among us understand methane much at all, although, like CO2, it arises naturally from swamps and the like and is also a valuable energy source in its more popular form a/k/a natural gas. The fractivists have put out numerous papers suggesting, for instance, we can’t rid of the methane, once it’s dumped into the atmosphere, for a century or so and, therefore, it’s far worse than CO2 as a greenhouse gas, blah, blah, blah…

But, now we learn that methane, just like CO2, can be absorbed by trees! A study titled “Global Atmospheric Methane Uptake by Upland Tree Woody Surfaces” was just published in Nature and the results are fascinating, to say the least. It’s an academic document, of course, but you’ll get the gist of it from the abstract (emphasis and pargraphing added):

Methane is an important greenhouse gas, but the role of trees in the methane budget remains uncertain. Although it has been shown that wetland and some upland trees can emit soil-derived methane at the stem base, it has also been suggested that upland trees can serve as a net sink for atmospheric methane.

Here we examine in situ woody surface methane exchange of upland tropical, temperate and boreal forest trees. We find that methane uptake on woody surfaces, in particular at and above about 2 m above the forest floor, can dominate the net ecosystem contribution of trees, resulting in a net tree methane sink.

Stable carbon isotope measurement of methane in woody surface chamber air and process-level investigations on extracted wood cores are consistent with methanotrophy, suggesting a microbially mediated drawdown of methane on and in tree woody surfaces and tissues.

By applying terrestrial laser scanning-derived allometry to quantify global forest tree woody surface area, a preliminary first estimate suggests that trees may contribute 24.6–49.9 Tg of atmospheric methane uptake globally. Our findings indicate that the climate benefits of tropical and temperate forest protection and reforestation may be greater than previously assumed.

The implications of this are huge, of course, and here are a few more items from the study:

Recently, we showed that mature trees in saturated soils can emit substantial quantities of soil-produced methane, which has been confirmed by others. In the Amazon, for example, flooded trees are the single largest emission source from the region. However, endophytic methane-using bacteria have been identified in temperate poplar trees and in tropical wetland tree bark, in which bark methanotrophy attenuated 36% of CH₄ emissions. Collectively, these lines of evidence raise the possibility that trees have the capacity not only to serve as an internal sink for otherwise emitted CH₄ but also, where soil CH₄ production is limited by low soil moisture, to serve as net sinks of atmospheric CH₄…

Collectively, these studies do, however, present the possibility that if higher portions of upland tree stems and branches are considered, then trees on free-draining soils may be net sinks of atmospheric CH₄. The net outcome of CH₄ emission and uptake processes associated with tree surfaces would depend on the hydrological status of the soil and the methane-consuming capacity of the tree surface area of exchange. The large surface area of tree stems, branches and twigs (hereafter referred to as woody surfaces) and the relative abundance of upland (herein referring to trees on free-draining soils with low water tables) versus wetland forests means that even small fluxes, in either direction (emission and uptake), may result in large cumulative exchanges of CH₄ associated with upland trees at the global scale…

We consider the CH₄ sink consequences of removing trees to be small relative to total biomass C loss; however, the impact of reforestation may be more significant. Despite the lower biomass of secondary forests, their large numbers of small trees mean that they often have high woody surface area, similar to or higher than that of old growth forests. We estimate an extra greenhouse gas mitigation value from CH₄ uptake as equivalent to 0.131 and 0.586 Mg of C ha⁻¹ yr⁻¹ in temperate and tropical forests, respectively, corresponding to a 7% and 12% extra climate benefit of new trees in these respective biomes. This suggests a possible global extra climate benefit, through the enlarged tree CH₄ sink, equivalent to up to 0.3 Pg of C yr⁻¹ or 1.1 Pg of CO₂-we yr⁻¹. This is equivalent to a 10% extra mitigation potential over benefits already estimated for expansion of temperate and tropical forests. Hence, the tree CH₄ sink may have a particularly important climate mitigation role in the context of reforestation, though this prediction needs to be tested through field studies in regrowing forests.

So, there you go. Trees and reforestation could substantially affect the amount of methane in the atmosphere. And, there are secondary implications as well. Obviously, clearing large swaths of woodlands for wind and solar facilities works counter to realizing the benefits of forestation. Moreover, covering land in the process of reversion to forest with solar panels doesn’t help either.

There will surely be more to come on this and a nice layman’s summary of the study may be found here. What we know for now is that trees matter and there are some fractivists out there crying in their beer right now.

#CH4 #CO2 #Nature #Methane #Trees #NaturalGas #Climate #Fractivists

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