Intra-annual dynamical persistent mechanisms in mediterranean ecosystems revealed SPOT-VEGETATION time series

Multi-temporal series of satellite SPOT-VEGETATION normalized difference of vegetation index (NDVI) and normalized difference infrared index (NDII) data from 1998 to 2003 were exploited for studying persistence in mediterranean ecosystems of the Sardinia region (southern Italy). Three different vegetation covers (shrub-land, transitional and forest) were analysed. The NDVI and NDII provide information on the vegetation status and water content, respectively. The detrended fluctuation analysis (DFA), which permits the detection of persistent properties in nonstationary signal fluctuations, was applied to the NDVI and NDII time series for the three vegetation covers. Our findings point out that the investigated ecosystems are characterized by persistent behaviour of NDVI and NDII, which means that they are governed by positive feedback mechanisms, which tend to destabilize the systems under external forces. The NDII exhibits a more persistent behaviour than NDVI, and the shrub-land shows a more persistent feature than the other two cover types.