Methane Fluxes from Living and Dead Trees in a Temperate Forest

Trees have been identified as an important source of methane in forest ecosystems, but little research exists on fluxes beyond their stems, such as those from foliage, branches, wounds, and coarse woody debris. Recent instrumentation advances allow rapid and accurate measurements of relatively low methane flux rates in-situ; this thesis takes advantage of such technology to explore methane fluxes from these tree components in northern hardwood forests of central Ontario, Canada. Foliage was found to represent a substantial component of forest methane budgets, acting as a sink in upland forests and a source in lowland forests (averages = -0.54, 6.06 nmol m-2 s-1; n = 27, 12, respectively). Uptake is hypothesized to occur through methanotrophs within foliage, and emissions from channelling of methane that originates in soil. In an upland site tree branches, wounds, and stems emitted methane (averages = 0.61, 10.58, 0.59 nmol m-2 s-1; n = 18, 83, 79, respectively), and at the stand scale represented 83%, 8%, and 9% of emissions from trees respectively. Emissions are hypothesized to occur through anoxic decomposition within the tree, which often occurs due to wounding. Coarse woody debris was found to act as a methane source in early decay classes and a sink in later decay classes (average flux rates ranged from 0.78 to -1.58 nmol m-2 s-1; n = 94). Immediately after harvest there was a large pulse of emissions from the cut surfaces of trees (>4000 nmol m-2 s-1 for Acer saccharum boles), but on average coarse woody debris was a methane sink in both managed and unmanaged stands. These results represent some of the first and most comprehensive in-situ methane flux measurements from tree branches, wounds, foliage, and coarse woody debris, and help to improve estimates of forest methane budgets. Inclusion of wounds and branches into calculations of tree methane fluxes will increase net emissions, but inclusion of upland foliage and dead wood as methane sinks can offset them. Strengthening forest methane sinks and reducing sources is an attractive policy option for “climate-smart” forestry, and this research can be built upon to support future efforts in this field.

Department dc:contributor.department

Forestry

Year dc:date.issued

2022

Author dc:creator

• Gorgolewski, Adam Stefan

Advisors dc:contributor.advisor

• Caspersen, John P
• Thomas, Sean C

• Forestry
• Methane budgets
• Methane sink
• Methane source
• Methanogens
• Methanotrophs

Handle dc:identifier.uri

http://hdl.handle.net/1807/125154

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/125154