Carbon-Use Efficiency of Terrestrial Ecosystems under Stress Conditions in South East Europe (MODIS, NASA)

Carbon Use Efficiency (CUE) is the ratio of net primary production (NPP) to gross primary production (GPP) and shows the capacity of terrestrial ecosystems to transfer carbon from the atmosphere to biomass. The aim of this study is to examine the CUE under the stress conditions using NPP/GPP data products from the MODIS (NASA) spectroradiometer for the period 2000– 2014. The drought reduced the CUE by 10 to 20% and, as a result, the region has shifted from a carbon sink to a carbon source. The stress affects mostly forest biomes, which are the lowest effective. The most significant impact on terrestrial ecosystems productivity and CUE are five-months-lasting droughts in terms of SPEI drought index. Drought also increases the variation of CUE. The degree of CUE reduction depends not only on drought strength, but also on its duration and the time of year when it occurs (perhaps phenophase). Further research is needed to understand the mechanisms of dependencies between CUE and the combination of high temperatures and water deficit conditions in terrestrial ecosystems.