Tropical Deciduous Forest, commonly called TDF for short, represent the most tropical parts of our region in the warm and protected canyons and slopes of southern Sonora. Although closely related and with a similar assemblage of tree species as thorn-scrub, TDF hosts more species of tropical origin. These species are generally sensitive to frost or need better and more consistent rainfall patterns to survive. TDF has a taller and more robust structure. A general rule of thumb is that trees in TDF rise above the tops of columnar cactus, while in thorn-scrub they do not.
Southern Sonora is the northern extent of this vegetation community, which survives in a zone between the Sierra Madre Occidental and the west coast of Mexico. TDF extends for over 500 miles to the south.