The popular image of a “jungle” evokes a landscape of dense, hot, and humid vegetation. Determining whether the United States contains such an environment requires examining strict ecological definitions, as the common understanding aligns with a specific type of biome. These biomes demand precise environmental conditions that are rare across the US geography. To find these ecosystems, one must look beyond the contiguous states and examine scientific criteria.
Understanding the Ecology of a Jungle
Ecologically, the term “jungle” is not a formal classification but rather a cultural term used to describe the understory of a tropical rainforest. This dense growth occurs where the forest canopy has been disturbed, allowing sunlight to reach the ground. The true scientific classification for this environment is the tropical rainforest biome, defined by two requirements: high year-round temperatures and extremely high annual precipitation.
Tropical rainforests are typically situated between the Tropic of Cancer and the Tropic of Capricorn, within 28 degrees of the equator. They require mean monthly temperatures that consistently exceed 64 degrees Fahrenheit (18 degrees Celsius) throughout the entire year, with minimal seasonal variation. A true tropical rainforest climate must receive substantial annual rainfall, generally exceeding 66 inches (1,680 millimeters), with no month receiving less than 2.4 inches (60 millimeters). This constant warmth and moisture sustain the incredible biodiversity and multi-layered structure of the forest.
Why the Continental US Lacks True Jungles
Applying strict ecological criteria shows that a true tropical rainforest cannot be found in the 48 contiguous US states. While areas of South Florida and the Gulf Coast appear jungle-like, they are technically classified as subtropical or tropical savanna biomes. The dense, swampy forests of the Florida Everglades, for example, are subtropical wetlands, not true tropical rainforests.
The primary factor preventing a true tropical biome in the continental US is seasonal temperature variation. The flat central corridor of North America allows Arctic cold fronts to occasionally penetrate deep into the southern states. These infrequent cold snaps and hard freezes disrupt the year-round consistency required for tropical flora to thrive. Tropical plants cannot survive the below-freezing temperatures that occur even in the southernmost parts of the mainland.
Another distinct type of forest often confused with a tropical jungle is the temperate rainforest, such as the Hoh Rainforest in the Pacific Northwest. While these areas receive massive amounts of rainfall, sometimes exceeding 100 inches annually, their climate is mild and cool, not hot. The temperate rainforest’s ecology is defined by its mild temperatures and cool, moist conditions. The lack of constant high temperatures and the presence of a distinct cool season disqualify these regions from the tropical classification.
Where US Jurisdiction Meets Tropical Rainforest
Despite the absence of true tropical rainforests in the continental US, the nation’s jurisdiction encompasses these environments through its non-contiguous states and territories. These locations fall within the necessary tropical latitudes, meeting the rigorous temperature and precipitation standards.
The most definitive example is El Yunque National Forest in Puerto Rico, the only tropical rainforest managed by the US National Forest System. El Yunque is a genuine tropical rainforest, classified under the Köppen climate type ‘Af’, receiving an average annual rainfall that can exceed 200 inches in some areas. The forest’s climate is characterized by consistent warmth, with seasonal temperature variation being virtually nonexistent. This allows for year-round growth and high biodiversity, supporting four distinct forest types within the park.
Another area hosting this biome is the state of Hawaii, particularly on the windward slopes of the larger islands. The Hawaiian tropical rainforests thrive in a warm climate with annual rainfall often exceeding 100 inches (2,500 millimeters). This is supplemented by persistent fog drip in montane regions. The slopes of Mount Waiʻaleʻale on Kauaʻi, for instance, are one of the wettest spots on Earth, fulfilling the ecological definition of a tropical rainforest.