Vegetation controls soil CO2 flux in a complex moist Appalachian Watershed

Background/Question/Methods

The controls on the spatial variability of CO₂ flux from watershed soils is poorly understood.  Recent work in the northern Rocky Mountains (USA) identified topographically driven lateral redistribution of soil water as the primary non-seasonal factor influencing spatial variability of CO₂ flux.  However, when those concepts were applied to a small watershed in the northern Appalachians, no relationship between flux and topography was found.  We established a study to identify the spatial controls on soil CO₂ flux in this small Appalachian watershed, testing the hypothesis that local site conditions, such as vegetation cover and soil properties, were of a greater impact on spatial variability of CO₂ flux than topography.  We identified three topographically similar locations, all <100m apart, with different vegetation cover; black cherry (Prunus serotina), American beech (Fagus grandifolia), and red spruce (Picea rubens).  Soil CO₂ efflux was monitored hourly over a 24 hour period at each site, four times through the growing season.

Results/Conclusions

Results show a typical seasonal pattern, but superimposed on this seasonality is the influence of vegetation, with the Fagus site having the highest flux values, and the Picea site always having the lowest.  We test these relationships against other spatial flux data collected through the watershed, and find good agreement, indicating that in moist, topographically complex eastern watersheds with heterogeneous vegetation, vegetation type, and resulting soil properties, may be the dominant control on spatial variability of soil CO₂ flux.