Fourth.—Region of Cupuliferæ and Betulaceæ, mostly oaks and alders, from 1585 to 3050 meters.
Fifth.—Higher region above 3050 meters.
Dr. Wagner calls special attention to a noted uniformity of the flora on the coasts of both oceans, and Professor Pittier affirms that the vegetation between Colon and Greytown on one side, and between Panama and San Juan del Sur on the other side, is remarkably uniform. The littoral zone has a width of about four maritime miles. The predominating flora is composed of Rhizophora mangle, Hippomane mancinella, Cocos nucifera, Chrysobalanus icaco, Crescentia cujete, Acacia spadicigera, Cæsalpinia bonducella and other Leguminosæ; Acrostichum aureum, Ipomœa pescapræ, Avicennia nitida, Uniola Pittierii and also Euphorbiaceæ, etc.
The zone of tropical forests shows, especially on the Atlantic side behind the coast region, a strip of from twenty to twenty-two miles in width, with lofty trees of Rubiaceæ, Myrtaceæ, Melastomaceæ, Sterculiaceæ, Euphorbiaceæ, Meliaceæ, Urticaceæ, Moraceæ, Anacardiacæ, Sapindaceæ, Leguminosæ and Palmæ. It is relatively free from ligneous undergrowth, having more monocotyledonous plants, such as Cycadeæ, Scitamineæ, Cannaceæ, Marantaceæ, Cyperaceæ, Filices and Bromeliaceæ, underneath. The latter orders figure, also with Orchideæ and Loranthaceæ among the epiphytes and parasites which cover the trees. Among the most characteristic plants of this region we name the coyol palm (Acrocomia), corozo (Attalea cohune), biscoyol (Bactris horrida), palmiche (Elæis melanococca) and Raphia nicaraguensis which forms almost forests along the River San Juan; further, Tecoma pentaphylla, Bombax ceiba, Eriodendron, Spondias, Croton gossypifolius, Hymenæa courbaril, rubber trees (Castilloa costaricencis and C. elastica), Geoffræa superba, Simaba cedron, species of Enterolobium, Cæsalpinia, Liquidambar, Copaifera, Cedrela, Swietenia, Sapota, Pithecolobium, Palicourea, Cinchona, Piper, Ficus, Cecropia; still further, smilax, vanilla, etc. Many of these characteristic plants are largely social, such as the piper, ferns, palms and others.
Moritz Wagner states that all along the southern limits of Costa Rica a likeness of climatic and geological conditions gives to the vegetation a nearly uniform character, while further northward a notable contrast is observed between the Atlantic and Pacific slopes of the mountain groups and on the interior terrace lands. The Atlantic slope, with more constant humidity of air, is characterized by vast, dense, evergreen, virgin forests, while the Pacific lands, with a relatively dry climate and rainless summer, present more open forests and savannas, with many deciduous trees and shrubs. However, deep river valleys and some slopes near the water-shed have dense, evergreen forests, and their vegetation does not differ much from that of the Atlantic slope. The flora of the high terrace lands has been so altered by thorough cultivation as to have almost lost its original character.
The Atlantic virgin forests, as well as those in the region of the San Juan River and of Lake Nicaragua, which comprise two-thirds of Costa Rican territory, show such a dense vegetation that its interior can be penetrated almost only by way of the rivers, and its general character and its enormous extension be studied only from high mountains. Owing to the very mountainous character of the country, over half of its area lies between 900 and 2100 meters above the sea, and is almost wholly covered with virgin forest. This forest here and there ascends still higher, reaching the upper limit of the oak region about 2700 meters above the sea.
Dr. Polakowsky, in an interesting publication entitled “Flora of Costa Rica,” calls the forest region of the San Juan River, in view of its luxuriant character, “The Central American Hylæa,” and this name Professor Pittier applies also to the entire Atlantic region, attributing to it a distinctly South American character.
The zone of the open forests and savannas, which has park-like features, is rarely found away from the Pacific side, where it forms a belt from sixteen to eighteen miles in width, interspersed with more densely forested river valleys, islands of higher and thicker virgin forests, isolated trees or groups of trees, sometimes also with catingas and meadows flecked with shrubs and matorrales.
The savannas and open forests spread to a considerable extent over Guanacaste, where they are a continuation of those of Rivas in Nicaragua; also over the plains of Terraba, especially in the region of Buenos Aires and Terraba; and over the coast-lands of Golfo Dulce. There are some small similar tracts near Alajuela, Turialba, Santa Clara and at some other points, as well as catingas and paramos in the high mountain ridges of the south. The paramos are found on poor soil and have a vegetation more herbaceous than ligneous, which, when moist, takes on the character of turf.
The trees of the savannas are generally of little height, excepting the Enterolobium cyclocarpum (the guanacaste), the pochote and ceiba. The grass lands are almost wholly composed of Gramineæ and Cyperaceæ, especially in the savannas of Guanacaste. The most characteristic plants are Digitaria marginata and Paspalum notatum, besides species of Setaria, Panicum, Eragrostis, Andropogon, Isolepis, Cyperus, Rhynchospora and Scleria, as well as of ferns (Pteris aquilina) and Schizæa occidentalis.