LAND-USE EFFECTS ON SOIL METHANE AND CARBON-DIOXIDE FLUXES IN FORESTSNEAR ITHACA, NEW-YORK

Consumption of atmospheric methane (CH4) and fluxes of carbon dioxide (CO2) were higher for soil in (i) mixed hardwood forest on historicall y unplowed land than in (ii) 80-year-old mixed hardwood forest and (ii i) 80-year-old conifer plantations both established on post-agricultur al land, whereas flux rates were lowest in (iv) adjoining agriculture sites, showing that past and present land-use in forest ecosystems aff ects fluxes of atmospheric CH4 and CO2. Site differences in CH4 fluxes were more pronounced in drier 1993 and 1995 than in wetter 1994, wher eas site differences in CO2 fluxes disappeared during winter and durin g pronounced drought in summer 1995. Seasonal variation in CH4 fluxes in forest sites were related to soil moisture but not CH4 concentratio ns in soil air. Notably, all four sites occasionally exhibited CH4 eff lux 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 w ere related to soil temperature and CO2 concentrations in soil air, bu t not in the agricultural site that maintained somewhat higher soil CO 2 levels. Future studies of soil CH4 and CO2 dynamics should recognize the persistent effects of historical (and recent) changes in land use .