Complex sentence: During fall, the only things that grow are mushrooms--a normal one and a poisonous one--in the Forest, and the hay grass, and in winter, nothing grows but the herbs in the forest cave, which grow all year round.
Split into simpler sentences: During fall, the only things that grow are mushrooms--a normal one and a poisonous one--in the Forest, and the hay grass. In winter, nothing grows but the herbs in the cave in the Forest, and they grow all year round.