Manual de Plantas de Costa Rica 151 
melaeaceae). Finally, numerous higher-elevation species occur here that belong to fam- 
ilies or genera with wide elevational distributions, e.g., Tapirira mexicana (Anacardia- 
ceae), Hieronyma oblonga (Euphorbiaceae), Manekia naranjoana (Piperaceae), Met- 
teniusa tessmanniana (Icacinaceae), Passiflora tica (Passifloraceae), and Elaeagia 
auriculata (Rubiaceae). 
This phenomenon of elevational distribution has been mentioned by Gentry (1990) 
in a comparison at the family level among four Neotropical rain forests as well as for 
the Chocé lowlands of Colombia. Gentry also indicated that this phenomenon should 
probably be considered a local ecological effect rather than a reflection of far-reaching 
biogeographical trends (even though several of these families are Laurasian). 
Pacific slope (lowlands, valleys, and minor mountain ranges) 
The Pacific slope of Costa Rica, slightly larger than the Caribbean, has a territory 
of 26,585 km’, with a more or less definite seasonality, and is drained by a dense 
hydrological network with strong erosional power. As with the Caribbean slope, 
roughly one half (51.1%) of this area lies between O and 300 m elevation (Herrera, 
1985). Nevertheless, this slope has various isolated or subsidiary mountain ranges, sep- 
arated from the main cordilleras, a feature lacking on the Caribbean slope. Here, the 
coastline extends for 1254 km, accounting for over 85% of the total coastline of 
the country; the coast is irregular, and more or less concave, as viewed from land 
(Gomez P., 1986). 
The greater relief of the terrain (in comparison to that of the Caribbean side), the 
more marked seasonality (varying between one or two to five or six months; Herrera & 
Goémez P., 1993), and the greater diversity of life zones (from tropical dry forest to 
paramo; Tosi, 1969) contribute to the diversity of floristic patterns. Generally speaking, 
diversity in climate, flora, and vegetation patterns increases from the northwest toward 
the southeast. 
This region can be divided into two large biogeographical blocks: the northwestern 
and the southeastern coastal regions. The boundary between the two lies approximately 
between the Rio Grande de Tarcoles and Cerro Turrubares. 
Northwestern coastal region 
This area includes what we call the plains of Guanacaste and the Nicoya Peninsula. 
Plains of Guanacaste. Numerous species of both tropical dry and wet forest attain 
their northern distributional limits in the vicinity of Hacienda Inocentes and the Los AI- 
mendros station of Guanacaste National Park. The Cordillera de Guanacaste ends in the 
north approximately at this point (Hacienda Inocentes). Toward the boundary with 
Nicaragua (close to Pefias Blancas and the Rio Sapoa), the topography of this area 1s 
