Manual de Plantas de Costa Rica 139 
ip 
3 ASS 4s G at, 
Llanura de San Carlos near La Selva Biological Station, 
Euterpe and Socratea (1983) 
cuneata dominate the understory, but non-palms such as Asplundia uncinata, Clavija 
costaricana, Dieffenbachia longispatha, and Zamia neurophyllidia are also frequent. 
The hilliness of this region apparently contributes to its rich diversity; numerous 
species are found here only on the hills. This can be noted even in closely adjacent sites. 
For example, Casimirella ampla, Ferdinandusa panamensis, and Humiriastrum digu- 
ense, species frequent to very common in the hilly Tirimbina area (as confirmed by plot 
studies; see Delgado et al., 1997), have not been found in the course of long-term floris- 
tic inventories in the relatively low areas of nearby La Selva Biological Station (see 
Hammel, 1990; Wilbur et al., 1994) or are known there only (Ferdinandusa) from the 
hillier southern reaches of the property (B. Hammel, pers. obs.). Similarly, a study of 
plots in Boca Tapada showed that the presence and abundance of very common tree 
species such as Dialium guianense, Pentaclethra macroloba, Qualea paraensis, and 
Vochysia allenii vary according to the relief of the terrain (N. Zamora V., unpublished 
data). Likewise, a study of the distribution of large palms at La Selva Biological Sta- 
tion showed clearly that drainage conditions of the soil are very important for certain 
species, while others grow nearly everywhere (Clark, 1998). 
Disturbed forests of this zone are characterized by the abundance of such species 
as Acalypha diversifolia, Apeiba membranacea, Casearia arborea, Castilla elastica, 
Cecropia obtusifolia, Coussarea hondensis, Croton smithianus, Cyathea delgadii, 
Goethalsia meiantha, Hampea appendiculata, Henriettella odorata, H. tuberculosa, 
Laetia procera, Miconia affinis, M. prasina, M. punctata, M. trinervia, Ochroma pyra- 
midale, Psychotria elata, Simarouba amara, Trichospermum galeottii, T. grewiifolium, 
Vismia baccifera, and V. macrophylla. 
Crossed by numerous large rivers such as the San Carlos, Sarapiqui, and Puerto 
Viejo, which often flood, this region has many areas of swamp forest, harboring such 
