Conservation is the main theme of the book. The author's passionate advocacy for the survival of the earth's animal life and plant life is a powerful theme throughout the collection of essays that comprises High Tide in Tucson. When she and her friend visit the Hawaiian Islands and hike through the dormant volcano called Haleakala, she is amazed to see the fragile new ecosystem that had developed in the valley of the volcano. A beautiful plant called the silverwood grows in no other place in the world. Because the ecosystem that has emerged in the volcano is new, it is fragile and its longevity is uncertain. Until stiff fines were recently established, poachers and tourists would uproot the unusual plants so they could sell them or use them for their own purposes.