Humans need stability, but ecosystems need constant change. Humans laud a stable marriage, a stable economy and particularly a stable flight. Weddings, dismissals and rough landings cause tension and stress. While stress sucks, stability is a good thing. Since it is good for us, it must be good for ecosystems, we might assume. But it's not so.

Stability and change, of course, are fuzzy ideas that can mean different things to different people. Stability is commonly defined as freedom from change or resistance to change. That is a good start, but there is more to it.

Some questions have only two sides: a light switch is either on or off, a coin toss is either heads or tails, a woman is pregnant or not. In ecology, we call this "binomial" "bi" as in bicycle, meaning two. It's one or the other, and there is not much in between.

Ecosystems, however, function more like a rheostat, a dimmer switch or a volume control. Fine-tuning is essential. Like brightness or loudness, stability comes in small increments depending on circumstance.

Take, for example, "terra firma," the idea that our earth is stable. In 1912 in "Origins of Continents and Oceans," Alfred Wegener declared that continents moved about like plates floating on water. Scientists thought he was crazy. Maybe he was, but by 1963 a mere 50 years later, Tuso Wilson published an article in Scientific American titled "Continental Drift" that shocked the world. Wegener had been dead for 32 years.

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Our plate, the Juan de Fuca plate off the coast of Oregon, moves at a blistering rate of less than 3 inches per year. Anyone moving at that speed would be considered stable or maybe decomposing. Anyway, it certainly isn't something you need to warn your children about. But, over the long run, drifting continents slowly change global climate and interaction among species.

Fire, floods and hurricanes, on the other hand, can quickly and intensely change how ecosystems function. Last year's Hurricane Katrina certainly changed the South, and the 2002 Biscuit fire a 500,000-acre blaze west of Cave Junction changed how streams and forests function locally. Water retention is reduced, and the probability of flooding is increased. In addition, a new community of plants is now being selected from millions of seeds and spores continually raining down on the area, all competing for limited space and resources.

Continental drift is usually imperceptible and events like Katrina and Biscuit are blatantly apparent. Both are change; only the rate is different. So what in the world is stable? Although we may yearn for stability, it's a myth. Even the "solar constant" is not constant. The "balance of nature" is a myth. Constant change regardless of the rate is reality. From the slow drifting plates to the acute change associated with climatic extremes, ecosystems thrive on it.

In fact, nature constantly uses three major processes, birth or regeneration, growth and mortality to assure change. It's similar to term limits in politics. Limits mortality is the ultimate limit are established to assure responsive adaptation to constantly changing conditions well, maybe politics is not the best example.

For many, maintaining health has evolved into attempting to stop or significantly slow the aging process. Spending on cosmetic plastic surgery in the United States has reached $9.4 billion. This figure does not include the cost of cosmetics, drugs and herbals. Do we baby boomers actually believe we can stabilize aging the money seems to say yes, or are we just conveniently ignoring reality? Where is the line separating stability from stagnation?

In ecology, it's like trying to preserve old-growth or any age class, for that matter or trying to stop the processes that assure change, one of Mother Nature's prime objectives. Mother Nature speaks last and often with finality. If wisdom really does come with age, I hope to appreciate the instability that comes with growth.

Tom Atzet is a retired Forest Service ecologist living in Merlin. He can be reached at P.O. Box 1226, Merlin, OR 97532.