Background
The authors write that "the Normalized Difference Vegetation Index (NDVI), which acts as a proxy for the density and photosynthetic capacity of vegetation, is strongly correlated with leaf area index, aboveground biomass, community coverage, and phenological change (Tucker et al., 1985; Badeck et al., 2004; Lu, 2006; Levin et al., 2007; Ma et al., 2010," and they say that "trends in NDVI can thus be used to monitor changes in vegetation cover, productivity, phenology, as well as vegetation health status at both large spatial and long temporal scales (Myneni et al., 1997; Tucker et al., 2001; Nemani et al., 2003; Fang et al., 2001, 2004; Pettorelli et al., 2005; Cleland et al., 2007; de Jong et al., 2011)." And they additionally - and more specifically - note that "previous results have shown increasing NDVI trends evident at a national scale, with large spatial heterogeneity (Piao et al., 2003; Fang et al., 2004)" for China.

What was done
In a review paper on the subject, Zhao et al. provide an overview of "the current status of large-scale vegetation studies using remote sensing techniques in China to understand the temporal and spatial patterns of vegetation activity in China over the past few decades, the inter-annual variations of phenology for the main vegetation types, and desertification status - particularly regarding vegetation degradation in arid and semi-arid regions."

What was learned
In the words of the three Chinese researchers, "over the past 2-3 decades our review shows that the satellite-derived index (NDVI) during the growing season and the vegetation net primary productivity in major terrestrial ecosystems (for example forests, grasslands, shrubs, and croplands) have significantly increased."

What it means
One study after another continues to provide striking evidence for the ongoing Greening of the Earth in which the great expanse of China plays a major role. Thus, the question we must now ask ourselves is: Has this transformation occurred in spite of or because of the documented contemporaneous increases in the air's CO2 concentration and temperature? Our entire website testifies to the fact that the latter of the two choices is the correct one.

References
Badeck, F.W., Bondeau, A., Bottcher, K., Doktor, D., Lucht, W., Schaber, J. and Sitch, S. 2004. Responses of spring phenology to climate change. New Phytologist 162: 295-309.

Cleland, E.E., Chuine, I., Menzel, A., Mooney, H.A. and Schwartz, M.D. 2007. Shifting plant phenology in response to global change. Trends in Ecology and Evolution 22: 357-365.

de Jong, R., de Bruin, S., de Wit, A., Schaepman, M.E. and Dent, D.L. 2011. Analysis of monotonic greening and browning trends from global NDVI time-series. Remote Sensing of the Environment 115: 692-702.

Fang, J.Y., Piao, S.L., He, J.S. and Ma, W.H. 2004. Increasing terrestrial vegetation activity in China, 1982-1999. Science China Series C 47: 229-240.

Fang, J.Y., Piao, S.L., Tang, Z.Y., Peng, C.H. and Ji, W. 2001. Interannual variability in net primary production and precipitation. Science 293: 1723a.

Levin, N., Shmida, A., Levanoni, O., Tamari, H. and Kark, S. 2007. Predicting mountain plant richness and rarity from space using satellite-derived vegetation indices. Diversity and Distributions 13: 692-703.

Ma, W.H., Fang, J.Y., Yang, Y.J. and Mohammat, A. 2010. Biomass carbon stocks and their changes in northern China's grasslands during 1982-2006. Science China Series C 53: 841-850.

Myneni, R.B., Keeling, C.D., Tucker, C.J., Asrar, G. and Nemani, R.R. 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature 386: 698-702.

Nemani, R.R., Keeling, C.D., Hashimoto, H., Jolly, W.M., Piper, S.C., Tucker, C.J., Myneni, R.B. and Running. S.W. 2003. Climate-driven increases in global terrestrial net primary production from 1982 to 1999. Science 300: 1560-1563.

Piao, S.L., Fang, J.Y., Zhou, L.M., Guo, Q.H., Henderson, M., Ji, W., Li, Y. and Tao, S. 2003. Interannual variations of monthly seasonal normalized difference vegetation index (NDVI) in China from 1982 to 1999. Journal of Geophysical Research 108: 4401-4413.

Pettorelli, N., Vik, J.O., Mysterud, A., Gaillard, J.M., Tucker, C.J. and Stenseth, N.C. 2005. Using the satellite-derived NDVI to assess ecological responses to environmental change. Trends in Ecology and Evolution 20: 503-510.

Tucker, C.J., Slayback, D.A., Pinzon, J.E., Los, S.O., Myneni, R.B. and Taylor, M.G. 2001. Higher northern latitude NDVI and growing season trends from 1982 to 1999. International Journal of Biometeorology 45: 184-190.

Tucker, C.J., Vanpraet, C.L., Sharman, M.J. and Van Ittersum, G. 1985. Satellite remote sensing of total herbaceous biomass production in the Senegalese Sahel: 1980-1984. Remote Sensing of the Environment 17: 233-249.