Land-use effects on soil methane and carbon dioxide fluxes in forests near Ithaca, New York

Consumption of atmospheric methane (CH4) and fluxes of carbon dioxide (CO2) were higher for soil in (i) mixed hardwood forest on historically unplowed land than in (ii) 80-year-old mixed hardwood forest and (iii) 80-year-old conifer plantations both established on post-agricultural land, whereas flux rates were lowest in (iv) adjoining agriculture sites, showing that past and present land-use in forest ecosystems affects fluxes of atmospheric CH4 and CO2. Site differences in CH4 fluxes were more pronounced in drier 1993 and 1995 than in wetter 1994, whereas site differences in CO2 fluxes disappeared during winter and during pronounced drought in summer 1995. Seasonal variation in CH4 fluxes in forest sites were related to soil moisture but not CH4 concentrations in soil air. Notably, all four sites occasionally exhibited CH4 efflux to the atmosphere, and studies confirmed the presence of anaerobic CH4-producing microorganisms (methanogens) in the soil, despite well-drained conditions. Seasonal variation in CO2 fluxes in forest sites were related to soil temperature and CO2 concentrations in soil air, but not in the agricultural site that maintained somewhat higher soil CO2 levels. Future studies of soil CH4 and CO2 dynamics should recognize the persistent effects of historical (and recent) changes in land use.