The sixth and seventh ecological zones are characterized by their shrubs and trees, and Presque Isle State Park is home to 633 plant species (195 monocotyledons, 410 dicotyledons, 5 gymnosperms, 5 horsetails, 13 ferns, and 5 mosses). The sixth zone, thicket and sub-climax forest, forms when shrubs grow on dying marshes, followed by small trees. The trees shade and thin out the thickets of shrubs, leading to a sub-climax forest. The seventh and final stage is climax forest, where many large trees form a canopy. If left undisturbed, this ecological succession is believed to take between 500 and 600 years, although visitors to parts of Presque Isle State Park can walk through all of these zones in .