U.S. regions in the tropical-to-temperate transition

A map showing North America's tropical-to-temperate transition zone. Red, orange, and yellow depict the more tropical zones, and blues depict the more temperate zones, based on to the coldest recorded temperature for each area between 1980 and 2009. Photos show some cold-sensitive plants and animals with northern range limits governed by winter cold temperature extremes. Credit: USGS. Public domain