Seasonal variation of the vegetated land surface across tropical South America was evaluated using Trajectory Analysis (TA) on the Pathfinder AVHRR Land (PAL) NDVI data. These 8 km 10-day maximum-value composite images of the Normalized Difference Vegetation Index (NDVI) span nearly two decades (7/81--12/99) that include several ENSO warm/cold phases. The derived trajectory established a baseline to assess the effect of climatic events related to the El Ni¿o/Southern Oscillation (ENSO) on the temporal development of the spatial dependence structure of the NDVI image time series. Results indicate that ENSO phases have significant effects on the spatial dependence structure of the land surface in Tropical South America that would be undetected, if the spatial domain of remotely sensed data were neglected. As such, TA provides an important technique for the assessment of the effects of global change and long-term land use/land cover transformations on phenologies of the vegetated land surface.