The USA's vanishing forests
By Peter Montague Trees are sick and dying everywhere in the US. At first blush this seems like an extreme statement. But a new book, The Dying of the Trees by Charles Little, will convince you it is true. This book gives a detailed picture of trees sick and dying. It seems clear that the dying trees are one more sign of danger, one more warning that something is terribly wrong. Why are the trees dying? The reasons are many and varied. In New England, New York, North Carolina, Tennessee, Georgia, Ohio, Indiana and Kentucky, it's a combination of acid rain and clear-cuts; in California it's killer smog; in Arizona and New Mexico and elsewhere, it's excessive ultraviolet light filtering through the earth's damaged ozone shield; other places, it's pesticides, or toxic heavy metals released by burning coal and oil; in Alaska and Florida it's rising temperatures and rising sea levels from global warming; in Colorado, Oregon and Washington state it's destructive forestry practices that leave forests weakened, unable to withstand extremes of weather or attacks by insects or fungi. In most places, it's probably combinations of all these factors. Scientists are playing catch-up now, conducting studies that may explain the complicated causes of widespread tree death. Answers come slowly. Hubert "Hub" Vogelmann, a botanist at the University of Vermont, wanted to study an undisturbed forest, so in 1965 he made a thorough survey of Camel's Hump, a 1245-metre peak in the Green Mountains. So far as he knew, he was describing a healthy ecosystem. He measured the types and sizes of the trees, and various other aspects of the ecosystem. He had no particular purpose in mind, other than to gather knowledge about nature. Periodically, he re-surveyed Camel's Hump, and a pattern began to emerge. The trees were dying. His survey in 1979, compared to the baseline study of 1965, showed a 48% loss of red spruce; a 73% loss of mountain maple; a 49% loss of striped maple; and a 35% loss of sugar maple. Vogelmann was able to show that the health of Camel's Hump had begun to decline in the period 1950-1960. Similar studies in the Black Forest of Germany, and in southern Canada, revealed that the most likely cause was acid rain. Acid rain occurs when coal and oil are burned, releasing sulfur which combines with rain (or fog or snow) to make acid precipitation. Acidity is measured in units called pH. Pure water has a pH of 7 — it is "neutral" — neither acidic nor alkaline. Pure rainwater has a pH of 5.6 — slightly acidic because, while in the air, rain absorbs carbon dioxide to form a weak solution of carbonic acid. After World War II the US saw a massive rise in use of fossil fuels, coal and oil. The resulting smoke was obvious, and obviously harmful; in Donora, Pennsylvania, in 1948, half the people in the town fell ill for three days because of coal smoke in the air. Twenty people died. In London in 1952, coal smoke killed 4000 people during a pollution episode. The official response in the 1950s was to build smokestacks hundreds of metres tall, to dilute the pollution. Today the Ohio River valley is still dotted by enormous coal-burning power plants with stacks as high as 200 or even 300 metres. These tall stacks allow the sulfurous pollution to travel 1500 km or more, where it forms acid rain across the Adirondack Mountains of New York, and across northern New England and southern Canada. In Vermont, the rain has a pH of 3.8 to 4.0. The pH scale is "logarithmic" so a change from normal (5.6) down to 4.6 means the rain has gotten 10 times as acidic; at 3.6 the rain is 100 times as acidic as normal. It wasn't until 1972 that Eugene Likens (then at Cornell University) and F. Herbert Bormann at Yale discovered acid rain. But meanwhile acid rain had been falling on northern New York and New England and on southern Canada for about 20 years. What Vogelmann has been able to show by studying Camel's Hump for 30 years is that acid rain doesn't affect just the trees; it affects the soil and thus the entire ecosystem. Soil contains a large amount of aluminium, but it occurs in the form of aluminium silicates; in that form, aluminium is not available to the roots of plants. But acid rain dissolves the silicates, releasing the aluminium and making it available to plants. When plants get aluminium into their roots and their vascular system, the roots clog, which prevents the plant from taking up adequate nutrients and water. The trees are weakened, and may then fall prey to extreme cold, or to insects or pathogens. Acid rain not only releases aluminium. It also releases other minerals — calcium, magnesium, phosphorus — which are fertiliser for the tree. Acid rain releases these fertilisers to be washed out of the soil, leaving the soil depleted of nutrients. That is not the end of the problem. The roots of many trees create a symbiotic relationship with an orange-coloured sponge-like fungus called mycorrhiza. The tree roots provide sustenance to the mycorrhiza, and the mycorrhiza help the tree roots gather water and nutrients from the soil. But acid rain kills mycorrhiza, thus further reducing the ability of trees to absorb water and nutrients. Acid rain also kills off portions of the detritus food chain. The detritus food chain is all the microscopic creatures that "compost" leaves, twigs, pine needles, dead branches and so forth, turning them back into soil. Because the detritus food chain is damaged by acid rain, forest "litter" builds up on the floor of the forest. The litter prevents new saplings from taking root — they cannot reach through the litter to make contact with the soil below. Furthermore, the litter promotes the growth of ferns, which give off substances that inhibit the growth of red spruce saplings, among others. This is not a complete description of problems caused by acid rain, but it gives a sense of the complexity of ecosystems and how they can become unbalanced by thoughtless human intrusions. Given the high rates of tree death and the widespread nature of the problem, one would think that the community of botanists, forest ecosystem specialists and US Forest Service employees would be up in arms, advocating change. But one would be disappointed. Throughout the book, Charles Little describes studies and statements by the US Forest Service downplaying the importance of tree disease and death. For example, in 1991 the Procter Maple Research Center at the University of Vermont pinpointed acid rain and other air pollution as an important cause of decline of sugar maples in Vermont. "We think we are looking at the early stages of an epidemic problem", the centre's report said. The following year the US Forest Service issued a report saying that 90% of the sugar maples surveyed were healthy and the overall numbers and volume of sugar maples was increasing. It turned out the Forest Service had used a tricky way of counting dead trees; only the standing dead were counted — those lying on the ground were not. Forest-protection activists in the Pacific north-west have long considered the Forest Service a rogue agency, captured by the forest products industry. Under the Reagan and Bush administrations, the situation grew so extreme that when Jack Ward Thomas took over the leadership of the Forest Service in 1992, he immediately issued six "messages" to personnel throughout the agency. The first three messages were: (1) Obey the law; (2) Tell the truth; (3) Implement ecosystem management. That such orders had to be issued speaks volumes about the past performance of this federal agency. In 1993 there was evidence of new candour in the Forest Service. A report issued that year said timber mortality, on a volume basis, had increased 24% between 1986 and 1991, "in all regions, on all ownerships, and for both hardwoods and softwoods". Hardwoods were particularly affected, and particularly in the south, where the mortality increase was 37%. [From
Rachel's Environment and Health Weekly.]