Harvest of warmth from fast-growing firewood

Here on the banks of the St. Lawrence River, in the northernmost point of New York State, Reynolds Metals Company is planting the fuel that within a few years will provide much of the heat the company needs to keep its massive factory complex warm in winter.

Reynolds, in short, is turning the unused lands around its plant into an energy bank.

Like some other companies pioneering home-produced energy, Reynolds - a houshold name because of the foil wrap it produces - has turned to trees, specifically the relatively new ''super poplars,'' as a fuel source for its boilers.

Reynolds hopes to demonstrate to others in industrial and commercial sectors that unused land can readily be utilized this way. Private landowners might even do the same.

Beginning with a small cuttings nursery last year, Reynolds expects to have 600 acres under the poplars by 1986, which will provide an annual harvest of 3, 000 tons of wood fuel - the equivalent of some 40 million cubic feet of natural gas or enough fuel to heat 105 homes for an entire winter season.

As Paul Tebo, who oversees the plantation project for Reynolds, sees it, ''every little bit helps. Whatever (oil or gas) we don't use to heat our plant means that that much more fuel remains in the ground for future generations or is available for the production of other products.'' Nitrogen fertilizers, for instance, are made from natural gas.

''When you produce the energy you need in your own backyard you save energy in two ways,'' Tebo points out. ''Not only is there a saving on oil or gas, but on the energy needed to transport it to the plant.''

Multiply what Reynolds is doing by the number of other concerns which could undertake a similar program and ''the little dent we are making (in the nation's oil and gas consumption) could become a mighty big one,'' he says. He sees the Reynolds poplar program as significant for the company itself, but even more significant for the United States in the example it presents.

Reynolds is one of two pioneering US companies with land to spare doing work with hybrid poplars. The other is Packaging Corporation of America in Filer City , Mich. A Canadian company, Domtar, Ltd., also has a major poplar program under way.

Poplars were frequently looked on as nothing more than a weed and as big a nuisance in the forest as the dandelion is to the front lawn. But now that same weedlike propensity is what makes it so sought after for fuel production.

Not every poplar grows as fast as the ''super'' varieties, which have become readily available by hybridizing vigorous trees found growing in the wild and then cloning the best of the progeny. Fortunately, poplars are easily propagated from cuttings. This means a single tree can readily become a forest of trees, all with almost identical characteristics simply by sticking pieces of the parent tree in the ground.

Growth of the trees is incredibly rapid. The 10-inch cuttings at Reynolds averaged 51/2 feet at the end of the first growing season. Within five years super poplars grow 17 to 20 feet tall with trunks 5 to 6 inches in diameter, large enough to be turned into stove wood or chips for industrial boilers.

In 10 years, however, the trees top 50 feet in height with trunks more than 8 inches across. In one Canadian hybrid poplar program a tree produced a 42 -inch-diameter trunk in 18 years. With most other tree species a forest giant of that size would be harvested only by the grandson of the man who planted it.

The poplar's value doesn't end with the first cutting, either. It promptly renews itself, growing even more rapidly than it did from a cutting because of its now established root system. Tests show that a poplar plantation can renew itself approximately four to five times before it begins to noticeably lose vigor and ''we have to start all over again,'' according to Maurice Demerritt, an expert on poplars with the US Forest Service in Durham, N.H.

Poplars, according to Demerritt, grow best in well-drained sandy loam with the water table not less that 3 feet and preferably no more than 10 feet deep. By getting too far away from this ideal soil situation into either heavy clay or very dry sand, even super poplars will grow like any other tree - slowly.

Little work has been done, so far, on the long-term effects of heavy tree cropping on the land. Fortunately, the poplar makes light demands on the soil, but ultimately some sort of soil-building program might be necessary, according to Demerritt.

The poplar isn't the only tree being looked at for energy production. In the South the US Department of Energy is working with sycamores, eastern cottonwood, and sweet gum for the more hilly sites. In Europe, particularly Sweden, much work is being done with vigorous willow species. Some preliminary indications suggest that poplars and willows, planted in alternate rows, complement one another, producing more fuel in a given time than either species does on its own.

In May 1981 Reynolds established its nursery by planting 23,000 cuttings on four acres of land. By year's end, the new trees, as tall as a man, yielded 110, 000 cuttings which, in turn, were planted out the following May in the first of the company's energy orchards.

Meanwhile, the original nursery stock, now with a vastly increased root system, grew back to produce many more cuttings. By 1986 the Reynolds energy plantations will cover some 600 acres ''which is as far as we plan to go at present,'' according to Mr. Tebo of Reynolds.

Anyone or any company interested in growing super poplars, either as an energy source or for the production of low-stress construction timber, should begin, says Demerritt, by contacting the US Forest Service in the state where the company is located.