By BETTINA BOXALL, TIMES STAFF WRITER CARSON CITY, Nev. — A drive into the Sierra Nevada can seem like a retreat from time, a return to landscapes unmolested by the 20th century. But though California’s signature mountain range remains largely undeveloped, it is far from unaltered. George E. Gruell has the photographs to prove it. The 74-year-old retired federal wildlife biologist hiked, bushwhacked and occasionally helicoptered his way to dozens of mountain spots recorded in photographs taken in the late 1800s and early 1900s. He hunted for the same peaks and boulders, the same vantage points. And when he found them, he took another photo. In a just-published book, Gruell matches the new and old images, showing how much the landscapes have changed. In scene after scene, the contemporary photographs document dense forest and lush growth. Their historical twins show leaner country in which the trees were fewer, the ground more open, the meadows more abundant. The face of the Sierra has filled in–and that, Gruell says, is not a good thing: not for wildlife, not for the forest and not for the future of the range’s ecosystems. It has filled in, he suggests, because of a number of factors. Heavy livestock grazing a century ago bared soil for tree seedlings to take root. Logging cleared the way for new growth. A comparatively wet climate cycle in the 1900s promoted tree growth.Most of all, decades of anti-fire policies banished flames, nature’s gardener, from thewoods. Fire needs to be brought back, Gruell argues, to return the Sierra to what it was.Gruell’s work, partly reimbursed by logging interests, touches on an impassioned debate about the Sierra Nevada’s vast forest land. Logging levels, the role of fire and the decline in wildlife have been the subject of fierce political and environmental battles for years. Both sides may be able to pluck support from Gruell’s work. He advocates prescribed burns–controlled, deliberate fires that many environmentalists favor as a way of clearing dense undergrowth.But Gruell also says that logging limits imposed on federal land in the last decade are too restrictive and that in many places, stands need to be thinned before a regimen of periodic prescribed burns can be started. Gruell is well aware that his work, “Fire in Sierra Nevada Forests: A Photographic Interpretation of Ecological Change Since 1849,” is more than just a picture book. Sitting last week in the study of his Carson City, Nev., home, he said it took him a while to find a publisher because of the work’s implications. “This publicly advocates [forest] management, which involves disturbing the landscape.And there are a great many people out there who don’t want any disturbance in the landscape,” he said. It is not the first time Gruell has said things not everyone wanted to hear. He started using repeat photography–taking photos of the same sites chronicled in historical photographs–early in his career.By documenting changes in the landscape, he could trace changes in wildlife habitat and thus influences on wildlife populations. Sometimes his findings didn’t reflect the common wisdom, but Gruell says he was never told to shut up.After retiring from the U.S. Forest Service in 1987, he started lecturing and consulting on fire ecology and fire’s effect on wildlife habitat. In 1992, the California Forestry Assn., a timber industry group, offered him a contract to conduct a repeat photographic study of the Sierra Nevada. He produced a brochure of about 20 photographs and wanted to do more. So he pursued the work on his own, poring over thousands of old photographs in historical libraries. When he came across scenes that were well identified or had distinguishing features, he made a copy and set out for the area with a camera, asking locals for guidance. Sometimes he found the spot from a road. Sometimes he hiked for hours off trails, clambering through bushes and scouring the ridgelines for vistas that matched the old ones.He couldn’t always find them the first time and had to return to some sites. For three photographs in which the view was blocked by trees, he used a helicopter to get the shot.A Ventura County native who smiles easily and played minor league baseball as a young man, Gruell is fit and lanky. He hunts, hikes and bicycles, so he was well-prepared for his back-country treks for the book. Gruell said he had been rejected by several publishers and was waiting to hear from another when he showed his manuscript to the Forest Foundation, a nonprofit group affiliated with the California Forest Products Commission, funded by industry companies.The foundation was interested in his work and paid him a fee that covered his expenses in developing the book. Gruell said the foundation also arranged to get copies of his book at cost from Mountain Press Publishing Co. in Montana, which issued it last month. Gruell said he that had no reservations about taking a fee from the foundation and that it exerted no influence on his work. “It’s an objective look at the landscape and what has happened,” Gruell said. He snapped his first repeat photographs with a 35-millimeter camera borrowed from his aunt while working for the Nevada fish and game department in the 1950s. When he joined the U.S. Forest Service in 1962, he started using large-format cameras belonging tothe service.Over the years, he produced series of repeat photographs from national forests in Nevada, Wyoming and parts of the northern Rockies. In the late 1970s, he went to work at the forest service’s fire research laboratory in Missoula, Mont. Again and again, his photographs showed that the landscape had been more open a century ago. Along with others, Gruell began to question the forest service policy of fighting fires and suppressing the natural fire cycle.Federal forest managers have in the last couple of decades retreated somewhat from that stance, undertaking some prescribed burns and allowing some wild-land fires to go unextinguished. But Gruell says the anti-fire mentality remains too entrenched, contributing to a number of problems. Without nature’s cycle of frequent fire to clean out undergrowth, the forest has become so dense that when fire does strike, it can reach catastrophic intensity. The relatively open “edge” areas that offer food for many kinds of wildlife have diminished. The tree canopy has become so thick that desirable plants beneath have declined.In places, he said, the Sierra resembles a jungle.