Characteristics of CO2 flux over a forest on complex topography

Abstract

The CO2 flux over a mixed forest of evergreen and deciduous broad-leaved trees on complex topography was measured by using an eddy covariance method. To evaluate the CO2 flux over such a forest and to ascertain the effect of topography, the eddy covariance measurement was conducted at the top of each of two meteorological towers erected in a basin (1.6 ha). The CO2 flux measured by the eddy covariance method was also evaluated by comparing it with the CO2 flux from leaf photosynthesis and soil respiration as continuously measured by automatic chamber methods on the forest floor and in the foliage. The daily variations in the daytime CO2flux values measured at the two towers were each quite similar. However, for the night-time CO2 flux values, there was about 36% difference between the towers, even though the flux was measured in the same basin. The CO2 flux as measured by eddy covariance and including CO2 storage change (Fn) was 60% lower than that estimated by the chamber methods (Fchm). The CO2 flux as measured by using the relation between Fn and soil temperature at 2 cm depth obtained only under conditions of low stability (U*≥ 0.25 m s−1) was 32% lower than Fchm.