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


Bassil El Masri1* (, Jessica Moon1, Gary Stinchcomb2, Benjamin R. K. Runkle3


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


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.