Complex sentence: Both male and female flowers can occur on the same tree, but it is more common to find all male and all female trees; a tree that is all male one year can produce female flowers the next, and similarly a female tree can become male.
Split into simpler sentences: Both male and female flowers can occur on the same tree, but it is more common to find all male and all female trees. A tree that is all male one year can produce female flowers the next, and similarly a female tree can become male.