The Osa Peninsula

The most biologically intense place on earth

The Osa Peninsula is located in the southern Pacific lowlands of Costa Rica, near the border with Panama and contains areas such as the Corcovado national park and the Golfo Dulce Forest Reserve. The forests of this region are the only moist or wet evergreen lowland forests that still exist on the Pacific coast of Central America.  The elevation ranges from sea level to 745 m on Cerro Rincón, Peninsula de Osa and the annual precipitation is up to 60 cm/year (~24 inches/year).; the soil types are diverse and the vegetation highly dynamic. The tallest trees exceed 150 feet in height.

The Costa Rica and western Panama mountain ranges serve as a giant barrier that separates moist and wet lowland rainforest species that originally dispersed from South America to both the Caribbean and southern Pacific lowlands. The mountains have caused reproductive isolation between populations of species that occurred in both areas. Over geologic time, the species diverged into separate species. This has contributed to a zone of endemism in the southern Pacific of Costa Rica.  Unfortunately, much of this region has been converted to pastureland and plantations for pineapple and African oil palm, and is now threatened by illegal logging, poaching and gold mining, which are common economic activities in local communities. Nevertheless, the worst environmental enemy for wildlife is global warming which will induce changes in communities of vegetation vegetation communities that are predicted to be large enough to affect biome integrity, and with it, the extinction of insects in the rainforest.

Named by National Geographic as “the most biologically intense place on earth,” the Osa Peninsula is a true jewel of land, water, and wildlife. Covering an area of just 700 square miles on the southern Pacific coast of Costa Rica, the Osa’s geological history makes it home to a nearly unparalleled amount of biodiversity. The Peninsula is estimated to house 2.5% of the biodiversity of the entire world – while covering less than a thousandth of a percent of its total surface area – truly earning its title as the most biological intense place on earth.

The Osa packs an unparalleled amount of land and marine species and diverse ecosystems in an incredibly small area, including:

  • The most significant wetland ecosystem and mangrove forests of Central America
  • The largest remaining tract of lowland rainforest in Pacific Mesoamerica
  • 2-3% of flora found nowhere else in the world
  • 323 endemic species of plants and vertebrates
  • The largest population of scarlet macaws in Central America
  • More than 4,000 vascular plants
  • More than 10,000 insects
  • More than 700 species of trees (which is more than all the Northern temperate regions combined)
  • 463 species of birds
  • 140 mammals, including a new record for Costa Rica made by our organization (
  • 4 species of sea turtles

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