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Abstract:
Satellite-derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation
productivity, is known to be correlated with temperature in northern ecosystems. This
relationship, however, may change over time following alternations in other environmental
factors. Here we show that above 30N, the strength of the relationship between the
interannual variability of growing season NDVI and temperature (partial correlation
coefficient RNDVI-GT) declined substantially between 1982 and 2011. This decrease in RNDVI-GT
is mainly observed in temperate and arctic ecosystems, and is also partly reproduced
by process-based ecosystem model results. In the temperate ecosystem, the decrease in
RNDVI-GT coincides with an increase in drought. In the arctic ecosystem, it may be related to a
nonlinear response of photosynthesis to temperature, increase of hot extreme days and
shrub expansion over grass-dominated tundra. Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming.
