This is a very hard level, which is one of the reasons you don't have to complete it to move on. The best advice here is:
- Focus on the left side of the map.
- Hatch a dragon as soon as you can, and have it harvest Life Essence from flowers as quickly as you can.
- Merge up the Life Essence to orbs, and use the Life Orbs to heal the land that has nests on it. It's tough, and may take some time.
- You should mostly ignore the Zomblins until you have extra dragons.