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An international team of researchers recovered ancient DNA from the bottom of an ice core that indicates the presence of pine, yew and alder trees as well as insects.
The researchers, led by Eske Willerslev of the University of Copenhagen, Denmark, say the findings are the first direct proof that there was forest in southern Greenland.
Included were genetic traces of butterflies, moths, flies and beetles, they report in Friday's edition of the journal Science.
The material was recovered from cores drilled through ice 1.2 miles thick at a site called Dye 3 in south central Greenland. Ice cores from another site farther north, 1.8 miles deep, did not yield any DNA.
Greenland was discovered by Vikings sailing from Iceland about 1,000 years ago. While it had an ice cap then, the climate was relatively mild and they were able to establish colonies in coastal areas. Those colonies later vanished as the climate cooled.
But the new research shows it hasn't always been so cold there.
"These findings allow us to make a more accurate environmental reconstruction of the time period from which these samples were taken, and what we've learned is that this part of the world was significantly warmer than most people thought," Martin Sharp, a glaciologist at the University of Alberta, Canada, and a co-author of the paper, said in a statement.
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 The base of the ice is mixed with mud and it was this mud that Willerslev's team studied.
The DNA, dated to between 450,000 and 800,000 years ago, may be the oldest yet recovered, according to the team. DNA found previously in the Siberian permafrost has been dated to 300,000 to 400,000 years ago.
However, because of uncertainties in interpreting the age estimates, they could not rule out the possibility that the newly found DNA dates to the last interglacial, 130,000 to 116,000 years ago.
The research was funded by the Carlsberg Foundation, National Science Foundation of Denmark, the Wellcome Trust, Natural Environment Research Council, European Union, the Natural Sciences and Engineering Research Council of Canada, McMaster University, the Polar Continental Shelf Project, Max Planck Society and the Swiss National Science Foundation.
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On the Net:
Science:
http://www.sciencemag.org
[Associated Press;
by Randolph E. Schmid]
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