Methane Dynamics of Vegetation-Soil Interactions in Bald Cypress and Other Bottomland Hardwood Forests

Authors

Bassil El Masri¹* (belmasri@murraystate.edu), Jessica Moon¹, Gary Stinchcomb², Benjamin R. K. Runkle³

Institutions

¹Murray State University, Murray, KY;  ²University of Memphis, Memphis, TN; ³University of Arkansas, Fayetteville, AR

Abstract

Methane (CH₄) is one of the most important greenhouse gases and more than 30% of its total emissions originate from wetlands. There is high uncertainty in the contribution of mineral soil wetlands to global CH₄ budgets. The project objectives are: (1) to improve the understanding of the controls on CH₄ fluxes in forested mineral soil wetlands; and (2) to better understand the effects of landscape position and forest composition on the CH₄ fluxes between terrestrial ecosystems and the atmosphere. Using a coupled modeling-experimental approach, researchers started measuring the spatial and temporal dynamics of CH₄ fluxes in soils and woody structures (stems and knees) of temperate bald cypress (Taxodium distichum) and other bottomland hardwood stands and incorporating the measurements into a land surface model to improve the model representation and predictions of CH₄ fluxes. Soil collars and custom-built chambers were installed in the stems and knees of trees along eight sites that span a hydrologic gradient from the terrace to the stream channel in Western Kentucky’s Clarks River National Wildlife Refuge (CRNWR). Results showed that the Cherry Bark Oak (Quercus stellate) stand was a greater soil CH₄ sink (-1.47 ± 0.60 nmol/m²/s) than a nearby Bald cypress stand (-0.44 ± 0.35 nmol/m²/s).

The team found significant differences in soil CH₄ fluxes (p-value < 0.02) between stand species composition (p-value < 0.02; T. distichum vs. rest of species, and Q. stellate vs. Quercus pagoda), but no significant differences in stem CH₄ fluxes among species (p-value = 0.25). Contrary to some studies, researchers found no significant difference among CH₄ fluxes across stem heights. There were significant differences among stem and soil fluxes (T. distichum: p-value = 0.01, Acer rubrum + Liquidambar styraciflua: p-value < 0.001). Soils took up CH₄, while stems emitted CH₄. The results showed higher average soil CH₄ uptake rate in high knee density areas compared to no knee areas (p = 0.004) that can offset the observed knees CH₄ emission. Researchers will use ongoing monitoring to improve the understanding of soil-vegetation interaction in hardwood bottomland wetlands and incorporate these functions into ongoing land surface modeling efforts.