The United States is home to diverse rainforest ecosystems, a fact that surprises many. These lush environments range from the cool, misty temperate rainforests found along its northern coasts to the warm, vibrant tropical rainforests in its island territories. The presence of these unique forests highlights the country’s varied geography and the surprising breadth of its natural heritage.
Defining US Rainforests
Rainforests are characterized by high annual precipitation and consistent humidity, fostering dense vegetation. They are broadly categorized into two main types: temperate and tropical. Temperate rainforests typically occur in mid-latitude regions, generally between 40° and 60° north or south of the equator. These forests experience mild temperatures throughout the year, usually ranging from 4 to 12 degrees Celsius (39 to 54 degrees Fahrenheit), and receive abundant moisture from both heavy rainfall and coastal fog. They often feature coniferous trees, alongside a rich understory of mosses and ferns.
Tropical rainforests, in contrast, are situated closer to the equator, within 23.5 degrees north or south latitude. They are defined by consistently high temperatures, typically exceeding 18 degrees Celsius (64 degrees Fahrenheit) year-round, with minimal seasonal fluctuation. These warmer conditions, combined with significant rainfall often exceeding 200 centimeters (80 inches) annually, support an extraordinarily high level of biodiversity. Tropical rainforests also maintain high humidity.
Where US Rainforests Are Found
Rainforests within the United States are found in distinct geographical areas, each with unique characteristics. The Pacific Northwest is home to temperate rainforests stretching from northern California up through Washington and into southeastern Alaska. A notable example is the Hoh Rain Forest in Olympic National Park, Washington, which receives an average of 3.6 to 4.3 meters (12 to 14 feet) of rain annually. This environment supports towering Sitka spruce and western hemlock trees, often draped in thick mosses and ferns, and provides habitat for Roosevelt elk.
Further north, Alaska’s Tongass National Forest stands as the largest national forest in the United States, encompassing over 6.8 million hectares (16.7 million acres). It represents the world’s largest intact temperate rainforest, featuring extensive old-growth cedar, Sitka spruce, and western hemlock trees. The Tongass is a haven for diverse wildlife, including bald eagles, moose, black bears, and all five species of Pacific salmon.
Tropical rainforests are located in the US territories, notably Hawaii and Puerto Rico. Hawaiian tropical rainforests span approximately 6,700 square kilometers (2,600 square miles) across the windward lowlands and montane regions of the islands. These forests vary in elevation from sea level to over 1,700 meters, with dominant tree species like `ōhiʻa lehua and koa forming the canopy. The isolation of these islands has fostered the evolution of many unique plant and animal species.
El Yunque National Forest in Puerto Rico is the only tropical rainforest managed by the U.S. Forest Service. Despite its smaller size of about 113 square kilometers (28,000 acres), it receives substantial rainfall, with some areas receiving over 5 meters (200 inches) annually. El Yunque boasts a rich variety of life, including numerous native tree, fern, and vertebrate species, notably the endangered Puerto Rican parrot. The rugged Luquillo Mountains contribute to the forest’s diverse microclimates.
Ecological Significance of US Rainforests
Rainforests in the United States are important centers of biological diversity, supporting a vast array of unique plant and animal species, many of which are found nowhere else.
These forests provide important ecological services. They play a role in regulating climate by absorbing atmospheric carbon dioxide through photosynthesis, effectively storing carbon within their biomass and soils. Temperate rainforests can hold over 900 metric tons of carbon per hectare, while tropical rainforests are highly efficient at carbon capture, with some individual trees storing substantial amounts.
Beyond carbon sequestration, rainforests contribute to water purification and regulate water cycles, which helps in mitigating floods and droughts by controlling water release. They also contribute to the global oxygen supply. These rainforests also hold cultural importance, particularly for indigenous communities who have maintained deep connections with these lands for thousands of years, relying on them for resources and cultural practices.