Standing Dead Trees: a Conduit for the Atmospheric Flux of Greenhouse Gases from Wetlands?

Wetlands represent the largest natural source of methane flux to the atmosphere, which can occur across the sediment/water/plant-atmosphere interface. Of these three potential methane sources, the role of vegetation in this flux is the least well understood. Both living and dead herbaceous vegetation have been demonstrated to act as methane sources, while knowledge regarding the contribution of woody vegetation to this flux is restricted to live plants. For dead woody vegetation to act as a methane source, two conditions must occur: (1) gas evolution/accumulation within the trunk airspace of a dead tree (e.g. snag) and (2) flux of this gas across the plant-atmosphere interface. The research presented here investigates condition (1) and provides evidence for a significant accumulation of both CH4 and CO2 in trunk airspace at water level (104.4 +/- 19.0 and 1785.5 +/- 470.7 mu L L-1 for CH4 and CO2 respectively) and CO2 at breast height (1257.6 +/- 294.4 mu L L-1) as compared to ambient air immediately outside the trunk (ca. 3 and 370 mu L L-1 for CH4 and CO2 respectively) in dead snags located within two ghost forest landscapes at the Timberlake Observatory for Wetland Restoration (Tyrrell County, North Carolina). A more finely resolved understanding of this potential pathway for methane flux to the atmosphere is important given the predicted increase in dead carbon stocks within coastal wetland ecosystems, as global climate change can lead to the conversion of these ecosystems into ghost forest landscapes.