What was done
In an area that extends from 72°02'N to 72°40'N and from 101°15'E to 102°06' E - a total of approximately 36,000 ha that includes the Ary-Mas forest (the northernmost forest on the planet) plus larch forests on southeastern slopes descending to the Khatanga River - the authors analyzed remote-sensing images made by Landsat satellites in 1973 and 2000.

What was learned
In the words of the authors, "the most significant changes were observed in the class of normal larch stands (canopy density > 0.3): their area increased by 66%," while "the areas of open and sparse forests (0.1 < canopy density < 0.3, and canopy density < 0.1) increased by 16 and 8%, respectively, whereas the background area became 19% smaller." In addition, they report that the rates of expansion of larch onto tundra "for sparse, open, and normal stands were estimated at 3, 9, and 11 m per year, respectively." However, they remark that "since sparse stands are at the forefront of advancement to the tundra, the rate for this class (approximately 3 m per year) should be regarded as the rate of larch expansion in general," and that "the above rates reflect not only the expansion of trees to the tundra, but also an increase in the density of sparse and open stands."

What it means
Kharuk et al. feel that the late 20th-century increases in the densities of larch stands in the Ary Mas forest and the expansion of larch onto what previously was tundra was "induced by climatic trends," and that the continuation of this process "will result in the expansion of larch to the Arctic coast," which they describe as a "phenomenon that took place in the Holocene [our italics]." Hence, it would appear that whatever is driving the forest changes they have chronicled (they mention temperature, to which we would add the aerial-fertilization and transpiration-reducing effects of atmospheric CO2 enrichment) is merely enabling forests such as the Ary Mas to reclaim that which had previously been lost by the progressive cooling of the planet after the Holocene Climatic Optimum, which cooling culminated in the record interglacial cold of the Little Ice Age from which the earth and its biosphere are now making an impressive comeback.