The ranks of sugar maple trees are dwindling throughout the northeastern United States, and at faster rates in Quebec and Ontario. In some places most of the once-leafy stands have been reduced to a tangle of naked branches. The forest floor seems to be spawning few young seedlings for replacement.
''It wasn't like this when I was a boy,'' says farmer Marvin Davis, as he kicks a decaying maple stump at his grove here. His stands have thinned by about 10 percent in the last few years. Although last winter brought a bumper crop of sap for maple syrup, he wonders how long it will be before his farm's output begins to dwindle.
''I've got lots of questions and no answers,'' he adds. ''We need help.''
But before they can offer help, scientists are trying to understand what is happening. In June, the Ontario Ministry of Interior launched what is scheduled to be a two-year examination into the cause of declining maple stocks. The Quebec Ministry of Energy and Resources is in the midst of a study that began in 1972.
In the United States, Sen. Patrick Leahy (D) of Vermont last month secured the promise of Senate Agriculture Appropriations Committee chairman Thad Cochran (R) of Mississippi for a $250,000 grant for sugar maple research at the University of Vermont. The US Forest Service is now contemplating an evaluation of the problem, to start as early as this fall.
The studies are coming at a time when the drumbeat of concern from farming interests and researchers continues to increase. Recent reports about the dramatic decline of many forests in Europe have pinpointed contamination by acid rain and air pollution as prime causes. Against a backdrop of similar discoveries about groves in North America, most investigators think that the current drop in maple population may be yet another symptom of a great underlying cause.
Some farmers in central Ontario's Parry Sound and Algonquin district have watched their groves dwindle by 60 percent over five years. There are reports of maple farmers in the Frontenac and Arthabaska regions of central Quebec going out of business, as attrition in their groves exceed 80 percent. Even regions considered less severely affected are reportedly experiencing mortality rates double or triple the normal annual rate of 2 percent.
But for all the accounts, no one really knows the extent of the damage. A helicopter survey by the Quebec government last year observed as many as 2 million dead maples over a 4,000-square-mile region. The University of Vermont has kept tabs on trees at nearby Camel's Hump Mountain for 30 years, noting a 25 percent decrease in maple stocks and an 87 percent decline in the number of young seedlings coming up since 1965.
But the vast majority of surveys are presently no more scientific than taking a stroll around one's yard.
''Actually we haven't noticed it being that bad around here,'' says E. Bradford Walker, director of the Vermont State Forestry Program at his Montpelier office. ''But I know something is happening out there.''
Theories abound as to what that ''something'' is. Defoliation by insects has been cited as one probable factor, as have cold, dry winters, droughts, and pathogens similar to those causing Dutch Elm disease. Some scientists have accused farmers of mismanaging their crops. Acid rain has been seen as perhaps a leading factor. The affected regions are known to be bathed in fog and soaked with rain made acidic by emissions from the industrial plants of the Ohio River Valley as well as the chemical and steel mills outside of Toronto.
''Acid rain is the primary factor,'' asserts Lise Robitaille, a forestry engineer heading up the Quebec Ministry of Energy and Resources' current survey. Forty case studies on individual stands were made last year as part of the effort, and 80 more are scheduled for this year.
Areas most heavily affected, she notes, had granite beds underneath. Where limestone-based soils - which tend to neutralize acidity - predominated, the problem was often lighter. In each situation, she says, soil samples revealed unusually high levels of such heavy metals as aluminum - presently thought to be a hallmark of acid rainfall.
A widely held theory is that the cumulative acid deposition from rainfall will alter a soil's chemistry, releasing such toxic metals as aluminum, which had earlier been innocuously bound in the soil. Once released, it damages fine roots of trees, preventing them from accumulating the critical nutrient phosphorous. Acid rain might also affect the leaves by preventing them from producing necessary sugars and other nutrients through photosynthesis, the process where carbon dioxide, water, and sunlight are turned to energy.
Once this happens the tree becomes vulnerable to attacks from insects, diseases, and other natural occurrences.
In turn, such onslaughts weaken the trees' defenses even further. When a tree's system gives way, it may have the withered appearance of a drought casualty. In fact, so the theory says, the tree has been essentially starved by acid rain deposition.
That theory is not accepted by all scientists. Some say soil conditions and susceptibility to acid deposition can vary from area to area.
''Acid rain is the best working hypothesis we have,'' says University of Vermont botanist Richard Klein. ''But we just don't have enough data or know enough about the problem to be absolute.'' Some researchers, he adds, are not positive that maple trees - or any of the hardwoods and conifers recently identified as victims - are even affected.
''It could be pretty easy to let this thing get out of hand,'' adds Philip Wargo of the New England Forest Experimental Station in New Hampshire.
He points to a 1977 study by the US Forest Service that examined 238 maple stands in New England and concluded that only 2 percent were in poor condition.
Nevertheless, others think the situation has become more severe since then.
''There are probably a dozen factors at work here,'' observes Sam Linzon, manager of phytotoxicology for the Ontario Ministry of Environment.
Says Mrs. Robitaille: ''It's too early to draw any conclusions.'' A large proportion of her team's data has yet to be analyzed. ''But it's quite plain that the condition is spiraling.''