Silence of the Song Trees by Branwen OShea

Young Cerulean's carefree life as a Firth is shattered when a planet-wide disaster wipes out all of his kind except him. The song trees that once harmonized to maintain the ecological balance of their shared planet Lenglood are silenced by the tragedy. Grief-stricken, Cerulean struggles to survive and awaken the dormant trees. But when human colonists show up, he has more to lose--the planet of Lenglood itself.