A new study from North Carolina State University finds that greenhouse gas
(GHG) emissions from standing dead trees in coastal wetland forests -
colloquially called "tree farts" - need to be accounted for when assessing
the environmental impact of so-called "ghost forests."
In the study, researchers compared the quantity and type of GHG emissions
from dead tree snags to emissions from the soil. While snags did not release
as much as the soils, they did increase GHG emissions of the overall
ecosystem by about 25 percent. Researchers say the findings show snags are
important for understanding the total environmental impact of the spread of
dead trees in coastal wetlands, known as ghost forests, on GHG emissions.
"Even though these standing dead trees are not emitting as much as the
soils, they're still emitting something, and they definitely need to be
accounted for," said the study's lead author Melinda Martinez, a graduate
student in forestry and environmental resources at NC State. "Even the
smallest fart counts."
In the study, researchers measured emissions of carbon dioxide, methane and
nitrous oxide from dead pine and bald cypress snags in five ghost forests on
the Albemarle-Pamlico Peninsula in North Carolina, where researchers have
been tracking the spread of ghost forests due to sea-level rise.
"The transition from forest to marsh from these disturbances is happening
quickly, and it's leaving behind many dead trees," Martinez said. "We expect
these ghost forests will continue to expand as the climate changes."
Using portable gas analyzers, researchers measured gases emitted by snags
and from soils in each forest in 2018 and 2019. Overall average emissions
from soils were approximately four times higher than average emissions from
snags in both years. And while snags did not contribute as much as soils,
researchers said they do contribute significantly to emissions.
In addition to finding that soils emit more GHGs than snags, the work lays
the foundation for the researchers' ongoing work to understand the role
snags are playing in emissions - whether they prevent emissions, like corks,
or release them like straws. That is an area of future research they're
currently continuing to explore.
"We started off this research wondering: Are these snags straws or corks?"
said study co-author Marcelo Ardón, associate professor of forestry and
environmental sciences at NC State. "Are they facilitating the release from
soils, or are they keeping the gases in? We think that they act as straws,
but as a filtered straw. They change those gases, as the gases move through
the snags."
Reference:
Martinez M, Ardón M. Drivers of greenhouse gas emissions from standing dead
trees in ghost forests. Biogeochemistry. 2021. doi:
10.1007/s10533-021-00797-5