Hoh Rainforest

The Hoh Rainforest is located on the Olympic Peninsula in western Washington state, USA. It is one of the largest temperate rainforests in the U.S. Within Olympic National Park, the forest is protected from commercial exploitation. This includes 24 miles (39 km) of low elevation forest 394 to 2,493 feet (120 to 760 m) along the Hoh River. The Hoh River valley was formed thousands of years ago by glaciers. Between the park boundary and the Pacific Ocean, 48 km (30 mi) of river, much of the forest has been logged within the last century, although many pockets of forest remain.

Flora

The dominant species in the rainforest are Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla); some grow to tremendous size, reaching 95 metres (312 ft) in height and 7 metres (23 ft) in diameter. Coast Douglas-fir (Pseudotsuga menziesii var. menziesii), western redcedar (Thuja plicata), bigleaf maple (Acer macrophyllum), red alder (Alnus rubra), vine maple (Acer circinatum), and black cottonwood (Populus trichocarpa) are also found throughout the forest.

Rainforest

Rainforests are forests characterized by high rainfall, with annual rainfall between 250 and 450 centimetres (98 and 177 in). There are two types of rainforest: tropical rainforest and temperate rainforest. The monsoon trough, alternatively known as the intertropical convergence zone, plays a significant role in creating the climatic conditions necessary for the Earth's tropical rainforests.

Around 40% to 75% of all biotic species are indigenous to the rainforests. It has been estimated that there may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests. Tropical rainforests have been called the "jewels of the Earth" and the "world's largest pharmacy", because over one quarter of natural medicines have been discovered there. Rainforests are also responsible for 28% of the world's oxygen turnover, sometimes misnamed oxygen production, processing it through photosynthesis from carbon dioxide and consuming it through respiration.