Evidence for A Weakening Relationship between Interannual Temperature Variability and Northern Vegetation Activity
Wednesday, 17 December 2014
Satellite derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation productivity, is known to be correlated with temperature in northern ecosystems. Here we show that above 30 oN, the strength of the relationship between the interannual variability of growing season NDVI and temperature (partial correlation coefficient RNDVI-GT) has declined substantially between 1982 and 2011, although with a heterogeneous spatial pattern. This decrease of RNDVI-GT is mainly observed in temperate and arctic ecosystems, and this phenomenon also partly reproduced by process-based ecosystem model results. In the northern temperate zone, the decrease of RNDVI-GT coincides with an increase of drought. In the arctic 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 decadal response of plants to ongoing warming.