In Lord of the Flies, a group of schoolboys is stranded on a deserted island and, with no "grown ups," it is difficult to know what to do in such extreme circumstances. The boys are conflicted and feel both sheer exhilaration and fear which leads some of them to act irrationally and with no consideration of consequences. Piggy and Ralph try to be what they think they should be and the conch allows them to call order in the confusion. However, Jack never has any real respect for the authority invested in the conch, speaking and acting out of turn and adding to the boys' confusion. Instead of quelling their fears, Jack increases them, compelling them to focus on the beast and its possible representations, on the darkness and the shadows and on the unknown- which is one of the representations of the forest or jungle.
The forest also creates conflict as, apart from the unknown, it is the major source of food- fruit and the pigs- and its trees make good shelters and its undergrowth makes a good resting place. Simon takes refuge there and ultimately, Ralph will hide there. So it is also representative of the possibilities that exist and reveals that it is what the boys do with the opportunities presented to them which defines their future.
These boys have never had to make life-changing decisions for themselves and they have not had to feel the effect of poor decisions or real failure as they have always been able to rely on adults. Now, if they forget the fire, it's going to change everything; if they don't have some kind of order, they cannot build shelters, care for each other and plan for rescue and if they do not work together, they can never overcome their fear of the unknown.
Even when Jack explores the forest, there are still elements that remain a mystery to him. He thinks that, if the beast existed, he would have seen it but, in reality, Jack sees only what he wants to. The forest then is the stumbling block to progress but it is also the very provider increasing the boys' struggle with their inner selves. It houses the beast, it is very dark and ominous and it changes from a fascinating to a terrifying place, depending on the shadows and the boys' state of mind. It represents the ultimate collision between what the boys should do and what they actually do.
The jungle in Lord of the Flies symbolizes fear and savagery. During the day, the jungle is difficult with its tangle of creepers and dense growth, but at night travel through the jungle was unthinkable to the boys. The darkness became absolute, uncanny in its ability to cast shadows and hide possible monsters or beasts. Early on in the novel, Ralph warns the boys against wandering needlessly in the jungle for their own protection and safety.
As the novel progresses, the jungle breeds and encourages the savagery within the boys; the forest becomes the suspected dwelling place of the Beast as well as the focal point of the boys' savage hunts and the brutal killing of the sow. Golding also reveals his symbol for "man's inherent illness" deep in the heart of the forest--the depraved Lord of the Flies.
I think it symbolizes fear---
"From the beginning of the novel, the boys struggle with fear of the unknown."
They fear what they cannot see, the parts of the island they haven’t explored...this has a large “unknown” element; they can’t see in the dark FOREST, they don’t know what’s on the island, etc...