Sleeping Beauty's enchanted castle stood in a forest. Little Red Riding Hood had to brave the woods to reach grandma's house. And in Christopher Robin's 100 acres, stuffed toys came to life. It just takes a quick look back at the fairy tales and fantasies we grew up with to see that forests have always been perceived as mysterious places, where things aren't always what they seem.

DRI's Dr. Dale Johnson has spent the last 24 years studying the facts about forests around the world, but he'd probably agree with what our childhood literature implies: forests are full of mysteries. Armed with a Ph.D. in Forest Soils, and the latest research techniques, Johnson has traveled the world-from Alaska to Costa Rica-to learn how forests work, particularly how plants and soils interact. And, in keeping with their enigmatic nature, he's found forests slow to divulge their secrets.

Borrowing from his standard lecture for the course he teaches at the University of Nevada, Reno, Johnson relates something of the history behind forest research. "In Germany, back in the late 1800s, they noticed a decline in forest areas where litter, the debris dropped by the trees and plants, was being raked up from the forest floor." That's when science begin to recognize the importance of the interactions between soils and plants, and the way nutrients cycle through a forest ecosystem. "Forests recycle 90 percent of their nutrients," explains Johnson. "The litter dropped by trees decomposes and nourishes them. That's why forests can grow such large biomass with very little nutrient input. They are self-sufficient."

If they're so self-sufficient, you might wonder why they need the scrutiny of Johnson and scientists like him. The reason, as is often the case with environmental research, has to do with the unavoidable impact of civilization onnature. Three decades ago, the focus was improving the productivity of commercial forests, often by fertilization. In the last two decades, the focus changed to things like rising atmospheric carbon dioxide, acid rain, and intensive forestry practices and how they affect the well-being of the world's forests. Over the years, Johnson has studied various aspects of them all. Often he's discovered as many new questions as answers.

Take the issue of rising atmospheric carbon dioxide. Some seven billion metric tons of carbon dioxide are released into the air each year, primarily from the burning of fossil fuels. Bear in mind that while carbon dioxide is a noxious waste product to us, it's food to trees. They pull it out of the air and use it to grow. Given this, it may be that trees could actually help mitigate the potential problems of rising carbon dioxide, and grow faster and better in the future. It sounds good, but as Johnson's current studies of ponderosa pines growing in carbon dioxide-enriched air point out, things aren't that simple.

For instance, there is the important issue of other nutrients. Forests depend on many nutrients in addition to carbon dioxide, and the availability of one can have a great effect on the usefulness of another. Nitrogen is one of the most important plant nutrients, and often the hardest to come by, especially in soils in the western United States.

Johnson says that trees can use nitrogen more efficiently under high levels of carbon dioxide, and thus can grow faster, even with limited amounts of available nitrogen. However, very low nitrogen can counteract any benefits from the extra carbon dioxide. "In extremely nitrogen-limited soils, we're getting no response to the elevated carbon dioxide."

There's also the issue of time. "We're seeing so far, that under the right conditions, extra carbon dioxide can help the growth of tree seedlings, but will that effect last as they grow and form a mature forest? There's some disagreement among us on this question." And since forests age much more slowly than scientists and their funding, it's nearly impossible to design and conduct the kind of study needed to settle this question.

But Johnson is excited about an upcoming opportunity to find at least part of the answer. He'll be participating in a study of pygmy oak trees in Florida. These trees grow only six to eight feet high and can form a mature, closed-canopy forest in a matter of four years, as opposed to generations. "It's a rare opportunity to track the whole cycle of a forest's growth, and see how its needs change."

While slow-growing forests present a problem to researchers who study them, they also have an impact on the forestry industry, which looks to science to find the best ways to grow and harvest timber. Johnson recently reported on a Tennessee study where the long-term effects of two different harvesting practices were compared.

In one area, only the harvested logs were removed from the forest. The slash-branches and other debris-was left to rot on the forest floor. In another area, the slash was removed. Then science stepped back and let nature take its course. Fifteen years later, in 1995, the researchers returned to sample the soils and see how the rotting debris had affected the nutrients in the soil. What they found was surprising. "The carbon and the nitrogen in those rotting logs did nothing to enrich the soil. It was gone," said Johnson. "The soil basically got no organic matter or nitrogen out of the decomposition of the slash left behind, only other kinds of nutrients like calcium."

What this may mean, in some forests at least, is that the timber industry has nothing to lose in the short term by cleaning up after itself, and that otherwise wasted timber slash could be used for fuel or other purposes. In the long term, however, fertilization to replace nutrients that are removed in slash may be needed to maintain productivity.

Johnson says it's not entirely clear why the decomposing debris didn't have some effect on the carbon and nitrogen in the forest soil, but has some theories based on a Truckee, California, study. "In Truckee, the slash was masticated, or cut up, and significantly raised levels of nitrogen and carbon in the soil. The size of the chips, and the climate, probably have something to do with that."

What does become clear after discussing the various projects Johnson has been involved in over the years, is that the influence of human activity on forests is never going to be easy to predict. "To a forest, `pollution' like carbon dioxide, oxides of nitrogen, or even logging slash may just be nutrients where and when nature didn't originally intend them. How different forest systems react will depend on a complicated balance of factors."

And even if researchers do come up with some clear-cut answers about the here and now, the future is sure to change things. "Atmospheric levels of nitrogen in China are on the rise because of increasing development there," says Johnson. "As that nitrogen moves across the globe and is eventually deposited, we may see some major effects on the growth of our own nitrogen-limited forests."

What those effects might be, of course, remains to be seen, and perhaps even predicted by Johnson and others in his field. One thing does seem sure, however, the forest will still hold secrets for science to unlock.
-Jackie Allen