Monitoring of vegetation ecosystems in Greece using vegetation indices time series

Περίληψη

Monitoring vegetation function on large temporal scales is very important in climate change studies. In this direction, satellite remote sensing plays a key role in the systematic monitoring of terrestrial ecosystems function by providing the required spatiotemporal thematic information either in global or in regional scale. In particular, vegetation phenology studying the timing of seasonal events such as lead budburst and leaf senescence are considered as indicators of ecosystem adaptive responses to climate conditions. In this study, a mountainous deciduous forest ecosystem (Fagus sylvatica) is studied in three different locations in Greece with different topographic characteristics. For each study area, NDVI and fAPAR time-series spanning from January 2003 to December 2011 are extracted from ENVISAT MERIS satellite data. Seasonal variations are observed and correlations between these parameters are performed in terms of the seasonal leaf growth cycle of the species. First results show high correlation between NDVI and fAPAR. There is also a general North-South gradient in the average monthly values and the correlation coefficient between the two parameters. However, observed NDVI saturation and fAPAR variability in summer months indicate that the altitude also plays a significant role in canopy d ensity and vitality explaining thus certain variationsfrom the general pattern. Ongoing comparisons to other ecophysiological parameters such as LAI, topographic and climate measurements aim at investigating potential relations and forest responses to local climatic conditions and topographic variations.