TERRA BELLA -- Inside the cavernous sawmill, a big log thundered across a metallic platform. Bam! It crashed into position on a cutting track. Shriek! A band saw sliced it into thick, cream-colored slabs. Another log rolled into place. The result: more noise, more boards and more conifer-scented sawdust that hung like a woodsy perfume in the air. The pace of the action was frantic. But it was also misleading. For by June, the Sierra Forest Products mill here may be out of business, stilled by years of dogged environmental opposition that have throttled the flow of national forest timber from the southern Sierra Nevada. If that happens, something more may disappear than the last sawmill south of the Tuolumne River. With it could go the best hope of managing the forest by thinning the dense stands of smaller trees sapping the health from the Sierra Nevada and fueling massive wildfires. "Without a mill, forest management will virtually cease in the southern Sierra," said Larry Duysen, the mill's logging superintendent. Two decades ago, more than 120 sawmills peppered California from Yreka to east of Los Angeles. But a steep drop in national forest logging has forced many to shut down. Now only 38 remain and about 8,000 workers have lost their jobs. None is more imperiled than Sierra Forest Products, a four-decade-old facility sandwiched between two orange groves along County Road 234 south of Porterville. Once, it ran two shifts -- now just one. Once, it employed 250 people -- now 130. Once, it had a mountain of logs available for cutting -- enough to last two years. Now less than six months' worth remain. But while the industry's decline may appear to be a victory for the environment, it also comes with a catch. With California's forests growing more dense and fire-prone every year, who -- or what -- will thin the woods? One answer can be found among the soot-black ridges and charred trees around Lake Arrowhead and Big Bear. In the 1980s, a sawmill -- the Big Bear Lumber Co. in Redlands -- worked the area. But when the San Bernardino National Forest ratcheted down logging because of environmental concerns, the mill struggled and died. The forest, though, kept growing. By the late 1990s, it was a tangle of trees competing for sunlight, moisture and nutrients. Then, drought struck. Trees grew weak -- and bark beetles finished them off. Stands that once glistened as green as Seven-Up bottles turned brown and yellow. Worried homeowners and federal land managers began to clear out the dead trees. But with no local mill, progress was too slow, and too costly. Vast quantities of wood were buried in a landfill or burned. In October 2003, huge wildfires ripped through the area. More than 1,000 homes were destroyed; six people died. Now, the southern swath of the Sierra Nevada "is starting to look like Big Bear seven, eight years ago," said Kent Duysen, general manager of Sierra Forest Products and Larry's brother. "We are encouraging the Forest Service to get geared up. Let's get ahead of the game." The Duysens' chief opponents are environmentalists. "Logging will increase, not decrease, fire risk," said Ara Marderosian, executive director of Sequoia ForestKeeper. "The time for compromise has ended; these forests are already depleted." But the Duysens have also found an unlikely ally in the environmental camp: Craig Thomas, director of the Sierra Nevada Forest Protection Campaign. "The service they provide, in terms of helping to reduce the fire hazard, is critically important," Thomas said. "All of us have an interest in them not going under." The brothers also are taking matters into their own hands. Over the past year, they have spent $2 million on new sawmill technology to cut the spindly trees most forestry experts say need to be cut. The super-sized Sierra Nevada woods in which the Duysens work have long inspired tremendous awe -- and epic conflict. But there is one thing most agree on: the area is turning into a tinderbox of unnaturally dense trees, the unintended consequence of decades of fire suppression and timber sales that targeted big, fire-resilient trees, leaving behind the smaller ones.