Abstract:
Costa Rica is on the trailing edge of the Carribean Plate, a plate that was initially produced over a hot spot, or mantle plume, in the Pacific Ocean during the Jurassic period (Mann 2007). The Carribean plate drifted through a gap that developed between Laurasia and Gondwana and it now rests between the North and South American continents. During the Cenozoic era, subduction of the Cocos plate has raised the western margin of the Caribbean plate, forming a volcanic arc from Panama and Costa Rica to Guatemala. The raised margin of the Carribean plate has formed a bridge connecting the North and South America. Oceanic terranes of the Santa Elena Peninsula and the Nicoya complex are exposed south of volcanoes in Nicaragua and west of volcanoes in Costa Rica (Fig. 1). The serpentine (ultramafic) terrain is on the Santa Elena Peninsula.
Most of the soils on the Santa Elena Peninsula are derived from weathered serpentinized peridotite, or serpentinite. The exposure of ultramafic rocks on the Peninsula is the only large one with ultramafic rocks along the Pacific margin of the Carribean plate, between Guatemala and Colombia (Lewis et al. 2006). As such, it represents a unique geoecological environment.
Savana perpetuated by frequent burning (Jiménez 2016) is the dominant cover on serpentine soils of the eastern two-thirds of the Santa Elena Peninsula, with dense forest on nonserpentine soils along the Rio Potrero Grande (Fig. 1), and nonultramafic soils along the northern margin of the Peninsula. Also, forest prevails on N-facing slopes on the western onethird of the Peninsula (Fig. 2). A landscape map was made of the serpentine area and Maria Marta Chavarria Diaz of the Area de Conservacíon Guanacaste and I characterized the soils and plant communities in the various landscapes. Maria Marta knew the plants very well and we were able to relate the distributions of the plant communities and soils to the different kinds of landscapes. There are no roads on the western one-third of the Santa Elena Peninsula, where the slopes are very steep, and access is difficult. With considerable oceanic influence and greater relief, up to 700 m, the vegetation differs substantially from that on the eastern two-thirds of the Peninsula, which lacks appreciable oceanic influence and the higher elevations are no more than about 300 m on the south to 500 m on the north. Dauphine and Grayum (2005) have a fascinating account of the vegetation and other biota on the western part of the Santa Elena Peninsula
