Simon goes to his "haven"--his place of solitude. He has his own place in the jungle, and that's where he retreats to when he wants to think or be alone. When he's in this place, he is able to see all the beauty of the island, rather than the ugliness that has developed with the presence of the boys. This part of chapter 3 explains his actions as he moves into his place.
Simon dropped the screen of leaves back into place. The slope of the bars of honey-colored sunlight decreased; they slid up the bushes, passed over the green candle-like buds, moved up toward the canopy, and darkness thickened under the trees. With the fading of the light the riotous colors died and the heat and urgency cooled away. The candle-buds stirred, their green sepals drew back a little and the white tips of the flowers rose delicately to meet the open air.