Manual de Plantas de Costa Rica
Vegetation
153
relatively flat to rolling, and no obvious geographic boundary exists between the Pacific and Caribbean slopes. Some of the elements of moist or wet forest that are found here are Amyris pinnata, Cecropia obtusifolia, Cnestidiumrufescens, Dendropanax arboreus, 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 amygdalina, Barleria oenotheroides, Celtis iguanaea, Clidemia sericea, Cochlospermum vitifolium, 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 activity, with induced fires associated with cattle and agriculture giving rise to much deforestation. When the Spaniards arrived, the whole Mesoamerican region had ca. 550,000 km2 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 national 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 general, 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 pantropical. 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 incana, C. pachaca, Ceiba aesculifolia, Colubrina arborescens, Cordia gerascanthus, Crateva palmed, Croton axillaris, Erythroxylum rotundifolium, Esenbeckia berlandieri, 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 trinervis, Schizachyrium malacostachyum, Schwenckia americana, Senna uniflora, Sida ciliaris, 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, encompassing the Santa Elena Peninsula and Punta Descartes. Geologically, the rocks of