Salt Lake residents need to plant thousands of trees if they want to help end global warming and make the urban environment nicer.

That was the message of R. Neil Sampson, vice president of the American Forestry Association, who visited Utah recently. The association, based in Washington, D.C., has launched an informational campaign to urge the improvement of forests, including urban forests, as part of the battle against global warming.The program is called "Global Releaf." The group maintains that tropical forests are being lost at the rate of 27 million acres a year. At the same time, more fossil fuel is burned than ever, releasing more carbon dioxide.

These factors might be connected with global warming due to the "greenhouse effect."

The tie-in with the forestry association is that trees absorb carbon dioxide and release oxygen. So the group believes Americans should plant 100 million new trees in the cities and towns by 1992.

Sampson said of deforestation and global warming, "I'm convinced of several things. One, it's affecting the carbon dioxide balance, and atmospheric carbon dioxide levels are up significantly in the last 30 years.

"Secondly, it's clearly affecting rainfall and water patterns in the tropics themselves. Now, beyond that, I happen to believe that the climatologists are right, that the greenhouse effect and the long-term warming trend are highly likely."

He conceded he is "less convinced that what we're seeing in these recent years is some early manifestation of that. I don't know that's been demonstrated."

Still, he said, "If we're going to do anything positive to head it off, we're going to have to do that a long time in advance, because it's going to work slowly."

The problem for groups like his, Sampson said, is that it wants to build public concern about what may be a serious problem, but at the same time, it doesn't want to trumpet "some false emergency."

But to be on the safe side, the group launched its program to plant 100 million trees in American communities. Los Angeles wants to plant 5 million, he said, and other communities have set goals for planting trees. So far, 32 states are involved, according to Sampson.

Citing a report by the forester for Salt Lake City, he said, "It looks like they've got 17,000 planting sites for new street trees." With 46,500 trees growing in the city, he said, the figures show there should be one-third more.

The city also needs to diversify its trees, he said. The report says most of the trees are from only eight species.

"Anybody who knows anything about ecosystems knows that a simple monoculture ecosystem is subject to disease," Sampson said. What's better is a healthy mix, as in a natural forest, he said.

"So Salt Lake City has some work to do. Over half its existing street trees are in a declining condition."

He complimented the city's recycling program by which recycled newsprint helps to pay for new plantings. Last year, the program generated almost $4,000, he said.

Scout troops and other groups are encouraged to plant trees, he said. Sampson invited those who are interested to contact the association at 1516 P Street, N.W., Washington, D.C. 20005 or to telephone him at (202) 667-3300.