Trees Shaping the Global Greenhouse Gas Dynamics

20.08.2018
Blog

There is a vast body of literature on trees’ role in tackling the greenhouse effect, especially by reducing CO2 emissions. As is known, during the Northern winter, as our green friends hibernate, the CO2 levels skyrocket globally. When summer finally arrives in the North, forests get back to work and absorb a huge cloud of CO2, bringing the levels down. Trees, in other words, have always been one of our main allies in battling the greenhouse effect. 

Did you know that trees have an important role in the exchange of methane, as well? According to recent research, it is not just livestock and rice plantations, et cetera, that release methane – plants do it too.

The volume of methane emissions from forest and plants seems lower, but significant nonetheless: up to 10-30% of the world’s total emissions. If true, this will require thorough examination and repair to our annual methane budgets

Boreal Forests as CH4 Source

 For this article, we interviewed Iikka Haikarainen, a doctoral student in Environmental Soil Science at Helsinki University’s Department of Agricultural Sciences. Haikarainen is part of a research group that focuses on emissions of CH4 (methane) from trees in boreal forest ecosystems. They are currently conducting research on greenhouse gases from soil and tree bark in Sweden.

Methane_emissions1

Generally, boreal forests have been conceived as an important methane sink, but Haikarainen’s research might prove us all wrong. The purpose of their research is to gain a deeper insight into the role of forests as methane source, which previous research has not placed much importance on. Their results point out that boreal forests might, in fact, have a more notable role in the global atmospheric methane budget than we thought.

The group is using Gasmet’s DX4040 gas analyzer for measurements in the forests of Sweden, and we were very eager to hear how their research was getting along, and how it was in line with the bigger picture of understanding the climate change.

Greenhouse Gas Emissions from Trees Are Common

Researchers have realized that especially in tropical rainforests, methane emissions from trees are, in fact, quite significant. In Haikarainen’s research, the measured greenhouse gas emissions remain lower, as they focus on the Boreal vegetation zone in the Northern hemisphere. He adds that in spite of methane exchange from tree trunks being lower than in the tropic, the phenomenon is taking place in wetlands in colder climate zones as well.

”Even though we know relatively little about the methane exchange in trees, there definitely is a lot of fluctuation between different vegetation zones and even between forest stands (a smaller unity of trees that share common characteristics)”, he explains. 

Methane Needs Low Water Table Level

According to Haikarainen, the methane that forests release develops in the anaerobic circumstances in the soil, where there is very little oxygen. These kinds of premises exist, for example, in woody marshlands where the water table level (WTL) stays fairly close to the Earth’s surface, approximately 5-30 cm deep. 

From these anaerobic circumstances in the soil, methane then starts to make its way to the root system and gets absorbed in the trunk as part of the natural oxygen exchange. It slowly rises up in the trunk towards the leaves, where it finally gets discharged as methane emissions.

Haikarainen adds that according to some findings, methane might even develop inside the tree. It is produced by the microorganisms that produce methane as the by-product of their methanogenic activity.

“In addition to CO2 and CH4, nitrous oxide (N2O) measurements are also getting in the mix in the study of greenhouse gas dynamics”, he explains.

Measurements with DX4040

Haikarainen’s research group chose DX4040 for measuring the gases due to its multicomponent capability. It was vital for the research that they were able to measure all three gases, CH4, CO2 and N20, simultaneously.

What is more, taking into consideration that the group worked outdoors, portability of the DX4040 was an asset. Upon measuring, the DX4040 analyzer was calibrated and placed on the ground near the subject. The analyzer was then attached to the tree trunk with siphons, which, in turn, were attached to the branches and leaves, where the gas concentrations were measured.

Methane_emissions2


New Horizons of Greenhouse Gas Dynamics

What kind of results is the research group expecting to get? According to Haikarainen, they hope to indicate that water table level (WTL) and temperature of the soil are the two main factors affecting the amount of methane trees release. In practice, the water table level dictates the location of the anaerobic activity in the soil. The deeper the WTL, the less likely the roots are to reach down to the pockets of methane in the soil.

As stated, methane emissions from trees might shape the way we think about the greenhouse gas dynamics all in all. Research such as Haikarainen’s, offers valuable and fresh information on natural greenhouse gases, and helps us connect the dots in the complex puzzle of climate change. What is more, that as the research develops, we need to be ready to take rapid action in adjusting the annual greenhouse gas budgets globally.

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Soil Flux Measurements Report

This study report compares six different technologies for measurements of greenhouse gases (GHGs) from the soil. Read the report and find out the agreement between different measurement technologies and suitabilities for GHG flux measurements from soil!

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