Both Mount Toby and the Holyoke Range are considered among the most biodiverse areas in New England. The trap rock Holyoke Range hosts a combination of microclimates including dry oak savannas, moist ravines dense with eastern hemlock and cooler climate plant species, and talus slopes, rich in nutrients, support a number of calcium-loving plants uncommon in Massachusetts. Fern and orchid species are particularly prolific on Mount Toby; forty-two of forty-five possible native fern species grow there as do rare orchids such as the showy lady slipper and the ram's head lady slipper.