The first thing a biologist wants to know about a piece of land or water is what lives there. Gather as many specialists as you can — a moth woman, a worm man — and take a census. It's the logical first step when a university acquires a new field station or the Nature Conservancy a new preserve. The urge to know what's there runs much deeper and wider, however. In the United States, for example, both the government and field biologists have long wanted to know everything that lives here in the whole country. People have tried to do that in Costa Rica, a very small country. We've tried, too.

A century ago the U.S. Biological Survey, a new division of the Department of Agriculture, set out to discover what we have in the way of living natural resources. It was no small effort. In Texas, for example, a dozen scientists and field agents worked from 1889 to 1906 at 178 different sites in all ten ecological regions of the state. As the years went by, however, the emphasis changed, and the division, by now a bureau, became part of today's U.S. Fish and Wildlife Service at the Department of the Interior.

In this decade the government made a new start on the original goal, with the formation of the National Biological Service within the Department of the Interior. In 1995 it produced Our Living Resources, a compilation of reports from scientists on what they were monitoring — and what they were finding. In 1996 the service was folded into the U.S. Geological Survey as a fourth major branch, the Biological Resources Division. And now this incarnation has produced the first comprehensive report, Status and Trends of the Nation's Biological Resources. By no means a complete census, it is more a synthesis of what we do know so far and a look at where we're going.

Now a 964-page government report, in two volumes no less, is not the first thing most of us would turn to for fun and relaxation. This one, however, may belong to a previously unknown phylum. The language is what computer people call "user friendly." It's loaded with color pictures, sidebars, tables, drawings and graphs. The big news, though, is the effect it has on the reader. In the process of detailing the sorts of problems our remaining wild things face, and going through region by region overviews, Status and Trends is a reminder of how much is still left, how many creatures and ecosystems the reader may have never seen. The logical response to Stock #024-001-00717-6 at the U.S. Government Printing Office would be to rush out to the airport, run up to any counter, and say: "Quick! Give me a ticket to anywhere," or simply drop to the ground (not on the sidewalk) with a magnifying glass.

The first part of the book is a minicourse in ecology, a discussion of forces that have an impact on our natural resources. Some forces are natural — hurricanes and volcanic eruptions. Some may or may not be natural, such as climate change. Some are our own handiwork: land use, water use, nonindigenous species, pollution and "harvest," meaning the mammals, birds, fish, shellfish, mushrooms, orchids and medicinal plants we remove. Those of us who live east of the Mississippi would do well to contemplate the maps showing the history of virgin old-growth forest in these United States. Most of ours is long gone. So we are hardly in a position to complain about what's going on today in the Pacific Northwest — or in Latin America, for that matter.

Climate change can give you a chill when you learn what it is that limits birds from extending their range northward. It has to do with how much fat a bird has left at dawn, when it can renew the search for food. (That's not a rule that can be extrapolated to humans. If it were, I could live comfortably at the North Pole.) Another way to say the same thing is that if a bird has to run its metabolism at more than 2.5 times the basal rate on a winter night, it won't make it.

Alien invaders are doing much better than I ever dreamed: New York may have lost the human population crown to California decades ago, but it maintains a lead in nonindigenous plant species, 1,122 to 1,113.

The second part of the book is the one that could send you to the airport. It describes trends in the biological resources of 14 regions of the country, with an additional chapter on our marine ecosystems. Each section provides a physical description of the region and outlines historical and current land use. It then describes the principle ecosystems to be found, giving their status and trends. Next it does the same for fishes, reptiles and amphibians, birds, mammals and, sometimes, invertebrates. Plants tend to be discussed in the ecosystem write-ups.

In the section on the Southeast, there is a sidebar on the southern tip of Texas, where the Rio Grande meets the Gulf of Mexico. (Texas west of the Pecos River appears in the Southwest section.) A habitat I'd never heard of, Tamaulipan brushland, hangs on by a thread there.

It comes in several varieties, but all consist of dense, woody and usually thorny vegetation, often interlaced with streams. Not very interesting or inviting, until you read that more than 600 vertebrate and 1,100 plant species are found there. The vertebrates include two rare cats, the jaguarundi and the ocelot. Chances of seeing either are vanishingly low, but it's nice to know they're still there.

Most of the trends reported in these volumes are, unsurprisingly, negative: declines in the numbers of individual species, declines in habitats such as wetlands. But there are surprises. In the section on grasslands, running up the center of the country from Texas to Canada, there are maps of the ranges of endemic bird species. The maps are color-coded, with shades of purple indicating declines and shades of green for increases.

On the maps, most of the birds appear to be holding their own, and some, photogenic ones like the ferruginous hawk and the Mississippi kite, are increasing across parts of their range. Some of it has to do only with shifts in where they breed, but it's nice to look at the maps and see more green than purple.

Nature isn't all handsome birds of prey. In the section on the Southwest, I came across cryptobiotic crusts found in arid lands: living layers on top of what would otherwise be bare soil. It never would have occurred to me that this crunchy stuff was alive, but apparently it is a community of blue-green algae (now also known as cyanobacteria), lichens, mosses, microfungi and bacteria. The "crust" is created whenever there's enough moisture for the algal filaments to move through the soil, leaving behind a mucilaginous substance that binds loose dirt particles. The crusts reduce wind erosion, store water when it rains, and add nitrogen and organic matter — both always in short supply in desert soils — to the ecosystem.

Pleasant little surprises pop up here and there. In the references for the section on Puerto Rico and the Virgin Islands, the name T. A. Wiewandt appears. This is Tom Wiewandt, a first-rate photographer whose work has appeared in this magazine. The reference is to his 1977 doctoral dissertation, "Ecology, behavior, and management of the Mona Island ground iguana, Cyclura stejnegeri." (Mona Island is a 13,633-acre wildlife refuge off the west coast of Puerto Rico.)

For the people who manage our natural resources, Status and Trends is an important beginning. For amateur naturalists, it is somewhere between a reference book and a travel guide. It is something I never thought I'd say of a government report: hard to put down.

By John P. Wiley, Jr.