The environment in "Lord of the Flies" shifts as the story progresses. At the start of the story, the island is described in terms that portray a nearly idyllic place. We learn right away that this is a lush tropical scene. The only ugly spot, the spot that lets the reader know this won't be a "Swiss Family Robinson" type of tale, is the "scar". We learn in the first pages that the two boys described first didn't know each other until this moment. This creates some curiosity and hints to us that the boys aren't here out of choice. Soon it becomes evident that a crash landing has occurred. When Jack marches the choir boys into the scene and we see how he acts, we know that there is going to be trouble because Jack is a bully from the first. He makes the boys march and wear their hot choir robes and hats even in the harsh tropical sun. This sets up the conflict between Ralph and his idealogies and Jack and his opposing ideologies. The island changes as the boys change becoming more and more sinister. The dead parachutist lands on the island creating the illusion of a physical beast. The boys hunt and kill. Simon talks to the Lord of the Flies - the skull of a dead pig. By the time we get to the end of the story, the island that we saw at the beginning as being a tropical paradise has become a scene of much death and a raging inferno.
The atmosphere in book progresses from almost idyllic to sinister and chaotic, and finally to empty and scoured out. The sense of joy and freedom the boys have in the beginning changes as Jack becomes more predatory and evil, Piggy insists on reason and Simon's consistent, but gentle, appeal to remain humane and human. The final moments are relatively bleak and exhausted as the survivors and rescuers realize how insane the situation had become.
While the physical environment is lush and life-supporting (fresh water and meat!), the island's configuration itself symbolizes separation and alienation - which is what the characters experience as they descend into savagery and chaos. The curious detachment the boys experience when they are rescued illustrates the confounding nature of islands: bleakness, and separation from human conformity with beauty and life-giving capabilities. Can we survive in isolation? Will savagery always prevail? How do we overcome such evil and barbarism?
The fire defines changes in the atmosphere and environment as well. At first the fire is needed for security, survival and rescue; later it becomes demonic and consuming, symbolic of a descent into nonhumanity.