Vegetation phenology dynamics from long term NDVI time series in La Pampa province

Abstract

Plant structure and function are natural indicators of environmental health and climatic trends, since photosynthetic activity allows to detect spatial and temporal variation. The evaluation of these trends at a regional scale is a challenging task due to shortages of multi-temporal inventories. Remote sensing has simplified the study of spatial distribution and dynamics of vegetation from an estimator of leaf area index and fraction of photosynthetically active radiation intercepted, known as the Normalized Green Index (NDVI). La Pampa province has a study of floristic composition and distribution at the landscape and regional scales, where degradation processes were recognized. The objective of this work was to characterize vegetation cover dynamics in La Pampa province from long term NDVI time series analysis, with different spatial and temporal resolution (MODIS and NOAA GIMMS). We specifically identified temporal NDVI patterns, characterized their typical biometrics, their variability under contrasting water availability and NDVI evolution over the last 31 years. Twenty four temporal patterns were detected and re-grouped into 8 clusters according to their most representative botanical component. Typical biometric parameters were defined for each group and significant changes were found for them under water stress condition. Photosynthetic activity increments were detected in the west of the province, consistent with shrubbing degradation processes. In the southeast and over the entire 500 mm isohyet region, significant reductions in the NDVI were identified process compatible with wood logging and shrubs clearance. We also detected a significant fall in the northeast NDVI, also compatible with changes in land use.