Nature is what I live in the city to get away from. “Turning Back,” the exhibition of works by Robert Adams now at the Matthew Marks Gallery is therefore a real challenge. To be in determinedly urbane Chelsea contemplating pictures of environmental degradation in Oregon takes me around several bends, especially since I come knowing that for the past several decades the United States has had an average net gain of 7 million acres of new forest every year.

Robert Adams is an important photographer for two reasons: the excellence of his work, of course, but also the impact this work, in conjunction with his writing and teaching, has had on the practice of landscape photography. Although Mr. Adams was born in New Jersey (in 1937), his grandfather took wide panorama pictures of the South Dakota plains, and Mr. Adams has made his own career mostly west of the Mississippi.

Mr. Adams studied his predecessors carefully, not just the big names like Timothy O’Sullivan, Eadweard Muybridge and Carleton Watkins, but the less renowned journeyman photographers who accompanied the mid-19thcentury geological and topographical surveys that introduced Americans to their Western domains. He meditated on the works of such 20th-century masters as Ansel Adams, Edward Weston, and Minor White. And he considered the way the West is shown on postcards, and the snapshots tourists take for their vacation albums.

But mostly he looked at what was out there, and noticed the ways in which it was different than the glorious pictures. There was development, much of it gimcrack and poorly planned. There was litter. There was spoilage in obtaining natural resources. There was smog that hid the distant vistas. He saw a new reality, was troubled by it, and devoted himself to recording it.

“On Humbug Mountain, Clatsop County, Oregon” (all the pictures are dated are 1999-2003), a 16-inch-by-20-inch black-and-white gelatin-silver print, is typical of many of the pictures in “Turning Back,” and the style is similar to much else in Mr. Adams’s work.The picture shows an area cleared of timber, which looks pretty awful. It is shot near the top of a hill, and the ground is littered with the detritus of the cutting: bits of branches and tree trunks cast about chaotically.The hilltop slopes down gently from each side so that a few distant hills can be seen in the shallow crotch. The sky is a white blank, the lighting flat. It is not a terribly interesting picture.

Ansel Adams tells in his autobiography how the religious feelings he had in church as a young boy were invoked later by his experiences in the mountains; the pictures he took were meant to inspire a transcendental awe. Robert Adams specifically seeks to avoid such cosmic sensations. He wants to be objective, to present evidence, to make documents that can be kept on record. His images are not composed for modernist drama, but to facilitate an autopsy. The sky is empty because spectacular clouds would be distracting. When a picture hints at the glory of nature, it is usually juxtaposed with the image of a trashed Eden. This implies a utilitarian, even propagandistic, function for the photographs, and Mr. Adams certainly means to instruct.

The foreground of “Clatsop County, Oregon” has been cleared of trees. In the middle, a stump seems to have been pulled up so its roots are exposed. Beyond the cleared space is a wall of standing evergreens, and over head a few wispy clouds. Is it wrong that these trees were cut down? Timber is used for making paper and for construction, two activities vital to civilization. Will the area be replanted? And where is the beauty in all of this? There are other criteria for the success of a photograph than beauty, and if Mr. Adams’s intentions are pedagogical, perhaps that is the standard by which they should be judged.

“Sitka Spruce, Cape Blanco State Park, Curry County, Oregon” is a different order of image. This tree has a thick trunk and branches that grow parallel to the ground so it looks like a stack of wooden wagon wheels. Mr. Adams’s camera is close enough to the tree that it seems to be reaching out to engulf him. The even lighting exposes the texture of the bark and the fuzz of the needles on the upper branches. Some branches are broken, but there is no evidence I can see that this was done by men. This is an interesting picture, but what are we supposed to learn from it? The expectation of instruction is so great that the inclination to enjoy a picture is thwarted by the fear some lesson is being missed.

“On Humbug Mountain, Clatsop County, Oregon” is shot looking up a steep hill that has been cleared of trees. The light emphasizes the irregular contour of the hill. The majestic stand of fir trees that crowns the hill seems in danger of washing down be cause of the loss of ground cover. Here Mr. Adams has permitted himself the luxury of some drama, and it makes his case more effective.

Elsewhere, a series of pictures of poplar trees, all titled “Harney County, Oregon,” show him working changes on a subject. Some show poplars along a road with open plain behind and electric wires strung on poles running through the branches. A few are close-ups of the middle section of a poplar, and these, because of the dense texture of the leaves and branches, have great charm.

There are 137 pictures in “Turning Back,” and many of them are so similar I could not understand why they had not been edited down. And many pictures have the same name, which makes them difficult to discuss. Quibbles aside, the ability to look dispassionately at the environment, the aim of Mr. Adams and others in the New Topographers school, is a major accomplishment. Over a long career, Robert Adams has worked with intelligence and talent at a difficult task. It is in the nature of his project that not every photograph will please all comers.

I find it hard not to admire a man who can write, “No place is boring, if you’ve had a good night’s sleep and have a pocket full of unexposed film.”

Until February 25 (522 W. 24th Street, between Tenth and Eleventh Avenues, 212-243-0200).