Planting trees in snowy areas may worsen global warming as their canopies absorb sunlight which would otherwise be reflected by the snow, a study says.
The report suggests deforestation is not always harmful
The report in US journal Proceedings of the National Academy of Sciences says the pine forests of Europe, Siberia and Canada may contribute to warming.
Only tropical forests effectively cool the earth by absorbing carbon dioxide and creating clouds, the report says.
But the report's authors stress they are not advocating chopping down trees.
They say forests are a valuable resource and remain vital for bio-diversity, providing a home for animals and plants.
Scientists have long argued that planting and preserving forests helps reduce global warming because trees absorb carbon dioxide from the atmosphere and convert it to oxygen.
Trees also absorb water from the ground, helping to form clouds that shield the earth from sunlight.
But the report's findings, discussed last year at an American Geophysical Union meeting and now published in the Proceedings of the National Academy of Sciences, suggest planting forests indiscriminately may be counter-productive.
Rainforests do help stop global warming, the report says
"Our new study shows that only tropical rainforests are strongly beneficial in helping slow down global warming," Govindasamy Bala of the Lawrence Livermore National Laboratory says.
In cooler areas of the earth, tree cover helps store sunlight reflected by snow on the ground and this "cancels or exceeds" the net cooling effect, Mr Bala told the AFP news agency.
Another author of the report, Ken Caldeira of the Carnegie Institution, said the report suggested it is "more important to preserve and restore tropical forests than had been previously realised".
But, he told the Associated Press news agency, he was "a little concerned about this being misapplied as an excuse to chop down the forests in the name of saving the environment".
Computer models produced by the report's authors suggested deforestation in higher latitudes could reduce global warming.
Steven W Running, a professor of ecology at the University of Montana, praised the report's authors for "sparking a lively scientific discussion".
But Mr Running, who was not involved in the report, said it was too early to base policy on the report's conclusion that certain types of reforestation might be counter-productive.