The Diquís Delta or Térraba-Sierpe Delta, located on Costa Rica’s south Pacific coast, is one of the most important of Central America from the biological and cultural perspective.

The largest area of this delta belongs to the Very Humid Pre-montane Forest transition to Tropical life zones, which was replaced largely since 1940, initially by banana plantations and later by other agricultural crops such as the African palm and rice, as well as with forest plantations of introduced species like teak, melina and eucalyptus. Currently there are a few original forest fragments, mainly restricted to the steep hillside of mountains and the surrounding parts of riverbeds. There are expanses which were once used in agriculture and left abandoned; in these grow what is known as thick scrubs (tacotales) by the process of regeneration or secondary forests, in different stages of development.

There is also an important area of Humid Tropical Forest transition to Perhumid towards the coast, dominated by the presence of wetlands and mangroves, found within the Térraba-Sierpe Wetland National Park. The Térraba-Sierpe Wetland is a complex of environments that include tidal channels, large shores, mangroves, and forests, variety reflected in the rich and abundant flora and fauna that live there. A vast number of plant species give food and shelter to birds, deer, monkeys, raccoons, felines, snakes, and many others. Underwater, be it brackish or salty, live different species of reptiles, mollusks, crustaceans, and fish.

The high parts of the Coastal Range corresponding to the southern section (Cima de la Fila Retinto) are formed by the Very Humid Tropical Forest life zone and contain important areas conserving their natural state, which are more homogeneous. These peaks host important biodiversity of endangered and endemic species, still unprotected.

Despite the human activities developed in the study area, the flora and fauna existing on the Diquís Delta and its surroundings is characterized by a high diversity. The presence of natural forest patches (land and rain), and secondary forests, combined with the vicinity of important protected areas such as the Térraba-Sierpe Wetland National Park, the Golfo Dulce Forest Reserve, the Corcovado National Park and Isla del Caño National Park, among others, allow for the existence of significant biodiversity not only in numbers but also in characteristics.

Studies recently carried out by the National Museum record over 1 500 species in the Valley of Diquís area, distributed in different groups, namely: fungi, ferns, plants, birds, mammals, and butterflies, representing a considerable percentage of the total species of those groups documented for all the Osa Conservation Area (ACOSA).