In a monastery on the Tibetan plateau, monks swathed in crimson robes chant under silk hangings, in a murky hall heavy with the smell of yak butter. Photos of the exiled Tibetan spiritual leader, the Dalai Lama — seen by China as a splittist — are openly displayed, as if in defiance. But Chinese security forces have tightened their grasp on this region, and monasteries appear to be emptying out, gripped by an atmosphere of fear and loss.