Manual de Plantas de Costa Rica 153 
relatively flat to rolling, and no obvious geographic boundary exists between the Pa- 
cific and Caribbean slopes. Some of the elements of moist or wet forest that are found 
here are Amyris pinnata, Cecropia obtusifolia, Cnestidium rufescens, Dendropanax ar- 
boreus, Enterolobium schomburgkii, Inga oerstediana, Ochroma pyramidale, Otoba 
novogranatensis, Passiflora vitifolia, Pourouma bicolor, Schefflera morototoni, Senna 
undulata, Trigonia laevis, Virola koschnyi, Vochysia ferruginea, V. guatemalensis, and 
Xylopia frutescens. Some elements characteristic of dry forests are Ayapana amyg- 
dalina, Barleria oenotheroides, Celtis iguanaea, Clidemia sericea, Cochlospermum vi- 
tifolium, Curatella americana, Davilla kunthii, Declieuxia fruticosa, Hippocratea 
volubilis, Miconia albicans, Ouratea lucens, Sida linifolia, Waltheria glomerata, and 
W. indica. 
Historically, the dry forest has been one of the habitats most affected by human ac- 
tivity, with induced fires associated with cattle and agriculture giving rise to much de- 
forestation. When the Spaniards arrived, the whole Mesoamerican region had ca. 
550,000 km? of tropical dry forest (more than 10 times the present area of Costa Rica); 
of that, less than 2% remains relatively pristine, and only 0.08% is designated as na- 
tional parkland or other conservation areas (Janzen, 1986). In Costa Rica, the largest 
tracts of protected, natural dry forest are in Guanacaste and Palo Verde National Parks. 
The first attempt to enumerate their flora was that of Janzen & Liesner (1980). In gen- 
eral, the major proportion of this flora is made up of species ranging southward from 
Mexico or Guatemala. A good portion of these species also reach Panama, and some as 
far as northern Colombia, Venezuela, and the Guianas; still others are shared with the 
Antilles, and the remainder are either widespread in the American tropics or pan- 
tropical. Some of the species that do appear to reach their southern limit in this driest 
part of the country are Agave seemanniana, Amphipterygium adstringens, Apoplanesia 
paniculata, Bourreria litoralis, Bursera graveolens, B. schlechtendalii, Capparis in- 
cana, C. pachaca, Ceiba aesculifolia, Colubrina arborescens, Cordia gerascanthus, 
Crateva palmeri, Croton axillaris, Erythroxylum rotundifolium, Esenbeckia berlandi- 
eri, Euphorbia colletioides, E. schlechtendalii, Forchhammeria pallida, Havardia 
campylacantha, Hybanthus calceolaria, Jacquinia nervosa, Jatropha costaricensis, 
Karwinskia calderonii, Krugiodendron ferreum, Lysiloma auritum, Martynia annua, 
Mimosa tricephala, Mortoniella pittieri, Morus celtidifolia, Pereskia lychnidiflora, 
Piptadenia flava, Piriqueta cistoides, Piscidia grandifolia, Pithecellobium furcatum, 
Plocosperma buxifolium, Podopterus mexicanus, Quercus oleoides, Rehdera triner- 
vis, Schizachyrium malacostachyum, Schwenckia americana, Senna uniflora, Sida ci- 
liaris, Sideroxylon stenospermum, Sphinga platyloba, Thouinia serrata, and Ziziphus 
guatemalensis. 
One of the most important areas of dry forest—not only in terms of diversity, but 
also for its geological history—is in the extreme northwest of the Pacific coast, en- 
compassing the Santa Elena Peninsula and Punta Descartes. Geologically, the rocks of 
