It is certainly purposeful on the part of author William Golding that the line of destruction through the pristine island that the damaged plane makes is referred to as "the scar"; for, it is an unnatural demarcation, caused by the ruin of trees and other vegetation. And, as the narrative of Lord of the Flies progresses, the boys themselves wreak more destruction and scarring: they burn much of the island, they turn over and send giant granite boulders crashing to the ground, they put their waste anywhere, and, finally, they nearly destroy the entire island.
In Chapter One, as the boys explore and climb the mountain, Jack Merridew points down, saying, "That's where we landed." As the boys look out over falls and cliffs, they see
a gash visible in the trees; there were splintered trunks and then the drag, leaving only a fringe of palms between the scar and the sea.
Later, in Chapter Eleven after Piggy is killed, Ralph must flee. In the final chapter, Ralph is pursued and his life is threatened as the savages set fire to the island. The scar which has some new growth and fallen, decaying trees is now threatened with fire, as well. No longer is there a "gash" in the island; the entire island burns and is threatened with destruction.