Impacts of pastoral grazing and climate change on vegetation cover in the central Chilean Andes

The central Chilean Andes present a unique and precious habitat for vegetation and animal species. However, that habitat is perceived to be under threat from both pastoral grazing and climate change. High-altitude summer grazing is a common pastoral management practice in the region. At the same time Central Chile has experienced a prolonged drought since 2010, with winter precipitation down by approximately 40% over the preceding decade, while average monthly temperatures have increased by about 1°C over the last 20 years.

This study investigates the temporal evolution of vegetation cover, over the period 2003-2022, in three neighbouring Andean catchments in Central Chile. The three catchments have experienced different pastoral grazing regimes during this period, which allows an assessment of the impact of pastoral grazing. Vegetation cover is analysed through a sequence of annual NDVI snapshots (MODIS imagery) over the period 2003-2022, taken towards the end of the grazing period in late summer. Data is represented as annual spatial maps, and as time-series of catchment vegetation cover.

Results indicate that all three study sites experienced a continual long-term decline in vegetation cover. Since the decline is similar in all three catchments, it cannot be unequivocally attributed to the pastoral grazing. Instead, the results suggest a strong correlation between temporal trends in key climate indicators (temperature, rainfall, evaporation soil moisture) and the declining NDVI, especially for seasonally-averaged temperature (R = - 0.75) and soil moisture (R = 0.76). The projected continuation of recent climatic trends suggests that the region’s high-altitude vegetation cover will continue to deteriorate in the coming years.