Spatial analysis of growing season length control over NEE

Using data from a large number of flux measurements, analysis of the annual net ecosystem exchange and the length of the carbon uptake period (CUP, number of days with negative flux) from observations suggest linear correlation between the two. The change in annual carbon uptake per CUP day differs significantly between forests and non-forests. Forest stands in this study are mostly young and regrowing. The ratio between mean daily carbon exchange rates during carbon uptake and release periods is conservative (2.73, with st.dv.1.08) for different vegetation types. It implies that a balance between carbon release and uptake periods exists despite different photosynthetic pathways, life forms, and leaf habits. The mean daily carbon sequestration rate of ecosystem never exceeds the carbon emission rate by more then four times. The growing season length derived from AVHRR NDVI data is closely related to the carbon uptake period and consequently can be used to approximate annual carbon exchange values of the ecosystems. The suggested approach has a potential for extrapolations of NEE over large areas from remotely sensed data, while most currently existing techniques still partially rely on modeling for respiration. Remote detection of growing season length in arid and cloud-covered ecosystem is problematic using data from AVHRR and requires improved, next generation remotely sensed data.