Background
The authors write that "Myneni et al. (1997, 1998) were the first to report evidence of the pan-Arctic increase in vegetation cover," noting that "by analyzing worldwide NDVI [Normalized Difference Vegetation Index] trends between 1981 and 1991, they showed that the greatest increase in photosynthetic activity occurred in regions above 50°N," and that "since then, this phenomenon has been observed for different regions," including Alaska (Silapaswan et al., 2001; Jia et al., 2003; Verbyla, 2008), Russia (Forbes et al., 2010), Western Canada (Olthof and Pouliot, 2010), over a longer time span (Jia et al., 2003; Goetz et al., 2005; Verbyla, 2008; Forbes et al., 2010; Olthof and Pouliot, 2010) and at a better resolution (Jia et al., 2003; Olthof and Pouliot, 2010).

What was done
Focusing on an area near the Boniface River research station 35 km east of Hudson Bay and 10 km south of the treeline in subarctic Quebec (Canada), Ropars and Boudreau evaluated changes in shrub cover over a full half-century, via their comparison of two aerial photographs taken in July 1957 and a satellite image of the same area obtained in July 2008.

What was learned
The efforts of the two researchers revealed that "both hilltops and terraces recorded an increase in shrub cover," and they say that "the increase was significantly greater on terraces than on hilltops (21.6% versus 11.6%)," while further noting that "this finding corroborates other studies using a similar method conducted in different regions of the Arctic," including Alaska (Sturm et al., 2001; Tape et al., 2006), northern Quebec (Tremblay, 2010), Russia (Forbes et al., 2010) and studies which revealed a major increase of the NDVI over the last few decades (Jia et al., 2003; Verbyla, 2008).

What it means
Ropars and Boudreau conclude their report by stating that "according to ground truthing, the shrub cover densification is associated mainly with an increase of Betula glandulosa Michx" - more commonly known as dwarf birch - and by noting that "the numerous seedlings observed during the ground truthing suggest that shrub densification should continue in the future," as, we would add, the warming- and CO2-induced greening of planet earth continues!

References
Forbes, B.C., Fauria, M.M. and Zetterberg, P. 2010. Russian Arctic warming and greening are closely tracked by tundra shrub willows. Global Change Biology 16: 1542-1554.

Goetz, S.J., Bunn, A.G., Fiske, G.J. and Houghton, R.A. 2005. Satellite-observed photosynthetic trends across boreal North America associated with climate and fire disturbance. Proceedings of the National Academy of Sciences 102: 13,521-13,525.

Jia, G.S.J., Epstein, H.E. and Walker, D.A. 2003. Greening of Arctic Alaska, 1981-2001. Geophysical Research Letters 30: 10.1029/2003GL018268.

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.

Myneni, R.B., Tucker, C.J., Asrar, G. and Keeling, C.D. 1998. Interannual variations in satellite-sensed vegetation index data from 1981 to 1991. Journal of Geophysical Research 103: 6145-6160.

Olthof, I. and Pouliot, D. 2010. Treeline vegetation composition and change in Canada's western Subarctic from AVHRR and canopy reflectance modeling. Remote Sensing of the Environment 114: 805-815.

Silapaswan, C.S., Verbyla, D.L. and McGuire, A.D. 2001. Land cover change on the Seward Peninsula: the use of remote sensing to evaluate the potential influences of climate warming on historical vegetation dynamics. Canadian Journal of Remote Sensing 27: 542-554.

Sturm, M., Racine, C. and Tape, K. 2001. Increasing shrub abundance in the Arctic. Nature 411: 546-547.

Tape, K., Sturm, M. and Racine, C. 2006. The evidence for shrub expansion in Northern Alaska and the Pan-Arctic. Global Change Biology 12: 686-702.

Tremblay, B. 2010. Augmentation recente du couvert ligneux erige dans les environs de Kangiqsualujjuaq (Nunavik, Quebec). Master Thesis, Universite du Quebec a Trois-Rivieres, Quebec, Canada.

Verbyla, D. 2008. The greening and browning of Alaska based on 1982-2003 satellite data. Global Ecology and Biogeography 17: 547-555.