The contiguous United States does not contain a true tropical rainforest, despite the common use of the term “jungle” to describe any dense, warm, and wet forest. While the US mainland hosts several lush and swampy ecosystems, they do not meet the strict scientific criteria for a tropical climate. A genuine tropical rainforest is defined by a specific set of climatic conditions that are simply not met within the 48 states.
Understanding the Tropical Climate Requirements
A true tropical rainforest, often classified as a Köppen climate type Af, requires high temperatures and heavy, consistent rainfall year-round. Scientifically, this environment is defined by having an average temperature of at least 18 degrees Celsius (64 degrees Fahrenheit) in its coldest month. It also cannot have a dry season, meaning every single month must receive a minimum of 60 millimeters (2.4 inches) of precipitation. These forests typically receive between 2,000 and 10,000 millimeters of rain annually.
This heat and moisture are necessary to support the biodiversity and multi-layered canopy structure characteristic of a tropical jungle. The vast majority of the contiguous United States falls into temperate or subtropical climate zones. These zones experience seasonal temperature changes, including a cool or cold winter period, which prevents the development of a true tropical ecosystem.
Closest Analogues in the Contiguous United States
The closest ecosystem to a tropical jungle in the US mainland is the Florida Everglades, a vast subtropical wetland. The climate here is a transition zone, often categorized as tropical savanna or monsoon, but it is not a true tropical rainforest. The monthly average temperatures are consistently warm, ranging from 18 to 28 degrees Celsius (63 to 82 degrees Fahrenheit) throughout the year.
The Everglades experiences a distinct dry season from November to April, which disqualifies it from the true tropical rainforest classification. This seasonal fluctuation results in a different type of plant and animal community adapted to periods of lower water levels. Further north, the Pacific Northwest contains temperate rainforests, such as those found in Washington state. These areas receive high amounts of rainfall, sometimes exceeding 3,500 millimeters (140 inches) annually, creating dense, wet forests.
The Pacific Northwest forests are fundamentally different because they lack the necessary year-round heat. Their temperate climate means they experience cool temperatures and distinct cold seasons, which dictates the type of flora, such as conifer trees, that dominates the landscape. These ecosystems are defined by their moisture but not by the constant heat required for a tropical environment.
True Tropical Rainforests in US Jurisdictions
To find a true tropical rainforest under US jurisdiction, one must look outside the 50 states and into its territories. The most notable example is El Yunque National Forest, located in Puerto Rico. El Yunque is the only true tropical rainforest managed by the US Forest Service.
This forest receives ample rainfall, with some areas recording between 3,050 and 6,100 millimeters (120 to 240 inches) annually, producing lush, dense foliage. The island’s location in the Caribbean provides the necessary latitude and air currents for warm and wet conditions. Other US territories, including the US Virgin Islands and American Samoa, also host tropical ecosystems. These locations provide the high temperatures and consistent rainfall that are absent from the contiguous United States.