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Despite the large scientific and conservation value of tropical very high elevation Andean ecosystems (above 4500 masl) little is known about environmental trends and ranges of variability. We combined satellite image analyses and dendrochronological methods to quantify changes in water balance and plant productivity of these ecosystems in northern Argentina and southern Bolivia through assessments of lake level fluctuation combined with instrumental climatic records at lower elevation; and to assess the relationships between water balance and two indices of plant productivity: tree ring width of the treelet Polylepis tarapacana and seasonal patterns of vegetation "greenness" (EVI) derived from satellite images. Between 1986 and 2007, inter-annual lake fluctuations were positively correlated with regional precipitation and de Martonne?s aridity index between, showing a decreasing trend during the period. Changes in lake size were correlated with radial growth of P. tarapacana, and with MODIS-derived annual EVI between 2001-2010; thus indicating that water balance has a significant effect on ecosystem functioning. A long term tree ring chronology indicated that recent trends of decreasing plant productivity and lakes size are still within the range of variability of the past 400 years, but such ranges may be exceeded in the coming decades if the trend persists.
