Greenhouse fact and fiction.

Concern over the steady buildup of "greenhouse gases" in the atmosphere and the likelihood that it could result in significant and very destructive global warming has captured front stage on the environmental agenda recently, and all indications are that global warming is here to stay as a critical environmental issue. In the process of seeking ways to slow the buildup of one greenhouse gas-carbon dioxide-the spotlight falls on trees and forests.

As a result, the public's interest in trees and forests is high, and the Association's Global ReLeaf campaign has helped direct this interest toward positive efforts to plant trees and improve forests everywhere. It has also caused policy makers to look at forests and forestry in a new light. If slowing the greenhouse effect becomes a national or worldwide priority, what are the implications for forest policies and programs? What are the practical opportunities to increase forest areas and growth, and what are the potential impacts on global warming?

We've started to study these questions, because we think the pressures for mitigating global warming could become a major societal justification for forestry programs. One way to get the input of AFA members and scholars on this question is to review what we think we know and don't know, and invite your comments and criticism. So here goes.

As with most environmental situations, we can fairly well define the extremes, but getting accurate estimates of the middle" situations is more difficult.

If someone gave us an area of forest land and told us to manage it for maximum beneficial greenhouse impact, our strategy would be something like the following:

1) Manage the trees to encourage maximum growth rates. (It is the growth of trees that converts carbon dioxide into sugars, cellulose, and oxygen. Building up biomass through growth is what results in net reduction of atmospheric carbon dioxide.)

2) As trees approach maturity and growth slows or stops, harvest them in a way that minimizes damage to topsoil and maximizes growth of the next crop of trees.

3) Convert as much of each tree as possible into products with a long storage life, such as structural building materials, and use the rest as fuel. (The latter use releases carbon dioxide back to the atmosphere, but since it replaces the use of fossil fuels, it represents recycling rather than a new net carbon addition to the atmosphere.)

4) Spread the ashes from burning the wood for fuel back on the land to help recycle nutrients; replant the land with the fastest-growing trees best adapted to the site, and start the management cycle over again.

If that prescription sounds too much like modern industrial forestry to suit your taste, look at it again. It wasn't intended to justify any particular type of land management or maximize all forest values-it simply focuses on creating maximum biomass and using that biomass in ways that reduce or constrain the buildup of atmospheric carbon dioxide. The truth is that in terms of favorable impact on the greenhouse effect, modern industrial forestry works pretty well. If we had more acres of forest, managed better, the atmosphere and the environment would be improved. The key factors are: fast timber growth; conversion of the wood into long-lasting, useful products; and rapid reforestation and regrowth.

An increasing number of voices today are using the greenhouse issue to support theories that trees should be planted but never harvested. Critics of old-growth timber harvest, for example, cite the cutting of old-growth trees as a practice that should be halted to help curb global warming. That argument simply won't stand up to the facts. Protecting old-growth ecosystems and properly managing old-growth forests for sustained production is a very important goal for managing some forests, and we've spoken out on it regularly. But from a strictly greenhouse effect, the world would be better off if those old trees were made into a bridge or a bungalow, and replaced by a new, fast-growing forest.

Let's look at the other extreme. If we were told to manage forest for the worst possible greenhouse impact, pact, we'd cut and burn the trees to convert most of the biomass into instant carbon dioxide. Then we'd keep the forest from regrowing, and encourage soil erosion, speeding the destruction of the organic matter in the soil and releasing the rest of the land's biomass to the atmosphere. When we got the land sterile enough that it wouldn't grow anything in the future, we'd have completed the job of maximizing the greenhouse effect on that land. "Ecotastrophe" would be accomplished.

If that prescription sounds uncomfortably like what we read and hear about in parts of the world today, it helps explain why the public is so concerned about tropical deforestation.

But what about the "middle" situations between these extreme examples?

Last summer's devastating fires in the Rocky Mountains had the same "greenhouse impact" in the short term as tropical deforestation does. Millions of tons of biomass that had been building up in those over-mature forests was instantly released into the atmosphere to contribute to the greenhouse effect. The only way to keep this situation from becoming a "worst case" scenario is to help hasten forest recovery rather than encouraging or allowing continued soil deterioration.

Happily, the pine ecosystems that characterize much of the Yellowstone region bounce back quickly after a fire. For the most part, reforestation will take place rapidly and efficiently under natural conditions. In some areas, repair of damage caused by firefighting is needed; in others, replanting or other land treatment may still be necessary. Thus, though the fires themselves had a very negative "greenhouse impact," the long-term damage will be lessened because of the nature of these sites and the efforts made by land managers to encourage rapid recovery. Many other forest regions in the country are significantly different from Yellowstone, however, and wildfires may not be followed by the recovery of a healthy forest, or any forest at all. Increasing incidence of wildfires (a likely scenario in the event of global warming) makes the management of forest lands for "greenhouse impact" even more difficult.

In terms of "greenhouse impact," however, the kind of "let-the-ecosystem-build-up-and-then-crash-due-to-natural (or unnatural) causes" management proposed by some people in the name of "environmentalism" doesn't offer much benefit-to either people or the environment. It simply recycles carbon on a one- or two-century time scale, with no net storage or reduction in the amount of carbon flowing between earth and air. So this kind of management would rate low on our "greenhouse scale." How low, and compared to what options? Those are questions that we need to know more about.

If we do begin to get significant global warming, huge acreages of mature or over-mature forests will become a significant greenhouse liability. As temperatures rise, the decomposition rates of organic matter go up rapidly, much faster than rates of tree growth, particularly in mature forests. This will result in forests that produce more net carbon dioxide than they take up, contributing to the greenhouse problem rather than helping solve it.

Under this deteriorating situation, and with drier climates, fires will become more common and natural reforestation less effective. This could make park and wilderness management very different in the next century than it has been in the past, with managers trying to decide between human interventions that will reduce the "natural" character of the ecosystem they are charged with protecting, or simply watching from the sidelines as an ecosystem set aside for public enjoyment is replaced by something quite different and perhaps far less enjoyable.

On managed forest lands, not all trees are managed for rapid growth, harvested efficiently, converted into longlived products, or rapidly replaced with thrifty, fast-growing forests. In other words, a lot of situations don't match our fictional "best case. " Most forests don't, in fact. So what can we say for sure about these situations?

From a standpoint of "greenhouse impact," a forest-management system will score higher if it results in rapid tree growth, both in the current crop and in each future crop, and also results in a high proportion of long-lived products that can keep carbon from recycling back to the atmosphere too rapidly. Since most forests today are converted into a variety of products ranging from chemicals to paper to manufactured wood to structural wood, we need to know the relative value of each type of product. Since there are various ways to enhance forest growth rates, and to protect the soil so that the next forest can grow rapidly, we need to know which management systems give the best "greenhouse impact."

Because of the importance of such new knowledge in guiding forest policy and management in the future, AFA has entered into a cooperative study with several federal and state agencies and universities to try to capture the best possible answers. Some of the other questions we will be asking, with the help of scientists all over America, are:

*What is the net effect on the carbon cycle of converting marginal cropland and pasture to forest?

*Can timber-stand improvements in existing forest increase net carbon fixation? How much?

* What is the storage life of different forest products?

* What impact can urban and community forests have on the carbon cycle, in terms of biological effect, and shading and energy conservation?

*How much net carbon-dioxide savings are possible by substituting wood as fuel for coal or oil, in such strategies as "energy plantations?"

We'll share the results of these inquiries in the pages of AMERICAN FORESTS and in technical publications over the coming year. In the meantime, we invite your comments and contributions. Our goal is to make sure the majority of the public-and public decision makers-can tell the difference between fact and fiction in this matter. AF