Manual de Plantas de Costa Rica 131 
particular mountain range. On the Pacific slope, the most diverse band appears to be at 
approximately (SO0—)600—1500 m in the northern cordilleras, at (7OO—)800—1500 m 
in the Cordillera Central, and at (400—)500—1500 m at the southern end of the Central 
Pacific region. On the Caribbean slope, this highest diversity band is somewhat lower, 
situated generally at (400—)500—1500 m. It may be that more species occur on the Pa- 
cific slope, overall, than on the Caribbean (see section on Analysis, below), perhaps due 
to a greater variety of habitats resulting from greater seasonality, even at the highest 
points such as the paramos (Luteyn, 1999). It bears emphasizing that most studies of 
floristic diversity account only for trees or (at best) woody plants. 
Caribbean slope (lowlands) 
The Caribbean slope covers an area of 24,115 km/, half lying between sea level and 300 
m (Herrera, 1985). Less than 15% (212 km) of the total Costa Rican coastline (1466 
km) is Caribbean, and in general aspect that coast is slightly convex, viewed from land 
(Gomez P., 1986). 
The Caribbean lowlands can be divided into two large subregions, the northern 
(better known as the “Zona Norte’) and the Caribbean or Atlantic. The elevational 
range we use to define both areas is 0-500 m. 
Northern region 
The northern region is subdivided into two large plains, the Llanura de Los Guatusos 
and the Llanura de San Carlos. This subdivision is supported floristically by the ob- 
servation that certain plant species present in both areas are more frequent in Los Gua- 
tusos than in San Carlos; furthermore, there are other differences in the floristic com- 
position as well as in the climate. It can be assumed that climatic differences across the 
region are a result of the interactions of influences from the Caribbean coast, the Gua- 
nacaste and Tilaran mountain ranges, the Rio San Juan, and Lake Nicaragua, proxim- 
ity to these features more or less determining local climate. 
Llanura de Los Guatusos. This plain is characterized by the predominance of moist 
forest, with a marked seasonality of three or four dry months (Herrera & Gomez P., 
1993). The topography is relatively flat, for the most part less than 100 m in elevation, 
and wetlands or flooded areas (see below) are common in the area. The floristic com- 
position of the region is unique, as it combines elements from both dry and wet forest. 
Dry forest elements may have entered the region by either of two routes: from the 
Pacific, by way of the narrow strip of lowlands between the end of the Cordillera de 
Guanacaste and Lake Nicaragua, or as a southward extension of the Yucatan-Petén veg- 
etation discussed below. Some of the species otherwise characteristic of dry forest that 
can be observed here are Acrocomia aculeata, Alibertia edulis, Aphelandra scabra, 
