Forest Decline: What's Putting Our Forests in Danger?

In 1985, forest decline was becoming a major concern worldwide. The MOTHER EARTH NEWS editors attempt to answer the question, what's putting our forests in danger?

| March/April 1985

  • 092-107-01
    In 1985, MOTHER EARTH NEWS' editors agreed that widespread forest decline was probably caused by a handful of pollutants.

  • 092-107-01

In 1982, the Federal Republic of Germany reported that 8 percent of its forests had lapsed into serious decline. A number of species showed yellowing, loss of leaves, deformed shoots, deteriorating roots, thinning crowns and loss of growth, and many trees had died. Cries of alarm went forth. But by the next year the damage estimate had grown to encompass a full 34 percent of Germany's forests — including 76 percent of all firs, more than 40 percent of spruce and pine and half of all the trees in the famous Bavarian and Black forests. The total area affected by such tree damage in Germany is now estimated to be almost 6,200,000 acres, and sick trees in other western European nations — such as Austria, Switzerland and France — bring the total threatened acreage to almost 10,000,000.

In the U.S. — after several years of sporadic reports of forest decline at high-elevation locations such as Camel's Hump, Vt., where 70 percent of the red spruce have died since 1964 — researchers around the country are beginning to confirm that forest decline isn't confined to the Northeast.

At altitudes above 6,300 feet on Mount Mitchell, N.C., and the surrounding Blue Ridge and Smoky Mountain peaks, the growth rate of red spruce and Fraser fir has dropped 40 percent since the early 1960s, and many trees have died. The defoliated white corpses of many of these evergreens stand as testimony to some new weakness ... one that can't be attributed solely to known natural causes. For example, though red spruce may have become more susceptible to the ravages of the balsam woolly aphid, a long-standing enemy, the effects of that pest don't explain the dieback of Fraser fir, which is immune to that insect's attack.

At lower elevations, the United States Forest Service has tentatively concluded, stands of southern yellow pine have for some reason experienced a 25 percent growth decline in the last 30 years. And researchers in the Ohio Valley have identified damage and growth declines of evergreens and hardwoods over an area stretching from Wisconsin through Indiana and Ohio. What's more, besides the well-known damage to evergreens in New England, maples in parts of Vermont have recently been found to be reproducing poorly and to have declined 25 percent in overall mass.

Toxic Pollutants

What's putting the world's forests in danger? Are these die-offs attributable to natural stresses? Few scientists believe so. More and more experts are concluding that the trees are succumbing, at least in part, to man-made pollution — in the forms of acid rain, ozone, nitrogen oxides, sulfur dioxide and toxic heavy metals. It may be that just one of these toxicants is overwhelming trees in isolated instances, but in general the problem seems to be the combined effects of all or many of these pollutants.

Because the Germans have such a serious problem, they've been quick to search for the specific causes of forest decline. Though German scientists were ready initially to place the blame on acid rain and the aluminum it can liberate from a bound state in soil, a closer look pointed out a number of deficiencies in that theory. For one, forest damage has been found in acid and alkaline soils alike. What's more, an examination of soil chemistry showed that natural (humic) acids in the organic litter layer on top of forest soil could be a much more powerful influence than low-pH rainfall, particularly in soils that lack calcium carbonate for buffering. In fact, if a cubic yard of 3.5-pH rain were to fall on a square yard of forest soil covered with a 2-inch layer of organic matter, the total acidity of the natural acids in the soil would be 500 times that of the rainfall. The effects of these natural acids, which might typically have a pH of 4.0 to 4.5, would easily outweigh the influence of acid rainfall, even though the rainfall might have a lower pH.


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