The Palo Verde National Park constitutes a mosaic of different floodplain habitats whose borders are marked by rivers and by a line of calcareous hills. The area is subject to large scale seasonal flooding. In the rainy season, due to the poor drainage, the plain floods through the combined action of rain, tides and the overflow from the Tempisque and Bebedero rivers. A wide expanse of the park’s swamps and lagoons and a sizable part of Guanacaste province are visible from the viewing points of Catalina and the Guayacán hills.
With over 12 different habitats, Palo Verde is one of the places with greatest ecological variety in Costa Rica. Among them are lagoons and brackish and freshwater swamps, the masses of zacaton grass with black mangrove (Avicennia germinans), mangroves, grassland with rough-leaf tree (Curatella americana), stunted forests of lowland mixed deciduous plains forests, mixed forests on calcareous hills, riverside or gallery forests, wooded savannahs, flooded forests and evergreen forests. In this protected area some 150 species of trees have been recorded.
One of the most conspicuous and the one that gives its name to the place is the horse bean (Parkinsonia aculeata), a thorny bush with light green leaves, branches and trunk and with delicate yellow flowers. This park contains the largest population of lignum-vitae (Guaiacum sanctum) in Costa Rica. It is a tree with extremely heavy and much appreciated wood and is seriously threatened with extinction.
One of the largest gatherings of waterfowl and waders in the whole of Central America occurs in Palo Verde. From September to March some 60 species, both resident and migratory, gather in the lagoons and neighbouring areas to feed and reproduce. Of these, those with the largest populations are the black-bellied tree duck (Dendrocygna autumnalis) with 25,000 birds, blue winged teal (Anas discors) with 15,000, and the wood stork (Mycteria americana) with 4000 birds. Other very conspicuous bird species are the jabiru (Jabiru mycteria), a threatened species with a population there of about 45 birds and scarlet macaws (Ara macaw), which already has almost disappeared from Guanacaste. Some 270 species of birds have been recorded in the park, of which 60 are aquatic.
On 2.3-hectare Pajaros Island on the River Tempisque 13 species of birds nest. It comprises a mangrove swamp and has the biggest nesting colony of black-crowned night heron (Nycticorax nycticorax) in Costa Rica. On the banks of the Rivers Tempisque and Bebedero you can see crocodiles (Crocodylus acutus) up to 5m long. In Botija, Bocana and Sonzapote Pre-Hispanic archeological remains have been found.
Palo Verde is part of the bio geographic unit known as “The Tempisque river Lowlands”. This park is on the Ramsar list of wetlands of international importance. Access to the offices in the Negritos sector is possible from Bagaces via Panamerican Highway - Tamarindo - Bagatzi (20 km) along partly paved and partly gravel roads. In the Catalina sector theres are path to Cerro Catalina, Bocana lagoon, Nicaragua lagoon, El Roble, La Palmita and the jetty.
There is also a camping site with tables, toilets and drinking water. In the Palo Verde Sector there are paths to Cueva del Tigre, Colmenal, Cerro Guayacán, La Venada and the Tempisque river (Chamorro jetty). The Palo Verde Biological Station is near the Palo Verde post. It is a centre of research into wetlands and dry forests run by the Organization of Tropical Studies (OTS). There is an educational route between the station and Guayacán Hill.