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NATURALIST'S GUIDE TO THE AMERICAS 



to 28C. on the coast and in certain 

 places of the interior, and 0C. or less 

 on the summit of the Andes. While 

 there is little variation during the course 

 of the year, the daily range increases 

 with the altitude. As is generally the 

 case all over tropical America, three 

 main belts of temperature are recognized 

 by the Venezuelans : the tierra caliente, 

 the tierra templada and the tierra 

 fria. They correspond more or less to 

 the Basal (0 to 1000 meters; mean tem- 

 perature 28 to 21 C.), the Intermediate 

 (1000 to 2800 meters; mean temperature 

 20 to 12) and the Upper Belts (2800 

 to 5000 meters; 12 to or less), so 

 designated for biological purposes (the 

 limits and mean temperatures given 

 here being those adapted to Venezuela). 



b. Rainfall and humidity. Most of 

 Venezuela is under the influence of the 

 monsoon, which governs the regime of 

 the rainfall. The parts most directly 

 exposed to this wind are either very 

 dry, with less than 800 mm. of annual 

 rain, or moderately humid, with 800 

 to 1500 mm. They include the coast 

 from Paria to Maracaibo, the Llanos 

 with the lower slopes of the surrounding 

 mountains, and the intermediary ranges 

 of the Caribbean system. In the ter- 

 ritory thus denned, the seasonal rhythm 

 is strongly marked, there being as a rule 

 a dry season ("verano") extending from 

 November to April, and a wet season 

 ("invierno") extending from May to 

 October. My experience is that both 

 the annual rhythm and the daily rain 

 offer no comparison as to regularity 

 with that personally observed during 

 fifteen years as Director of the Meteoro- 

 logical Observatory in San Jose of 

 Costa Rica. 



Certain parts of the lowlands present 

 topographic conditions which favor a 

 heavier forest. These are principally 

 the Orinoco Delta, the upper Rio Negro 

 and a limited area south of Lake Mara- 

 caibo. In these districts, the mean 

 annual rainfall is probably higher than 

 in most parts of the lowlands. Besides, 

 up to an altitude, that varies with the 

 importance of the mountain masses, 



the precipitation steadily increases, 

 and culminates in a belt in which rain- 

 forests appear, though with character- 

 istics distinct from the lowland for- 

 ests. Above this, the precipitation 

 decreases anew with the altitude, so 

 that the upper parts of the high moun- 

 tains constitute another dry belt. 



II. NATURAL BIOTA 



a. Evergreen forest 



1. Mangrove swamp. The mangrove 

 forests are dependent, not on the pre- 

 cipitation, but upon the ground water. 

 They are found at several points of the 

 littoral regions, especially, though not 

 always, at the estuaries of the large 

 rivers. The five species of trees (Rhizo- 

 phora Mangle, Laguncularia racemosa, 

 Avicennia tomentosa, A. officinalis and 

 Conocarpus erectus) which form such 

 forests, practically to the exclusion of 

 all others, thrive only in soils permeated 

 with salt or brackish water. Rhizo- 

 phora grows exclusively on soil per- 

 manently covered with sea water; its 

 peculiar adaptations are well known. 

 The other species are found in places 

 alternately dry and inundated, and 

 sometimes in brackish swamps where 

 they are mixed with Acrostichum au- 

 reum, Annona glacra and divers Cyper- 

 aceae. The principal mangrove forests 

 of Venezuela are situated at the mouth 

 of the Orinoco and the adjacent parts of 

 Golfo Triste, in the Gulf of Cumand, 

 around Piritii, Unare and Tacarigua 

 Lagoons, at El Carenero near Cape 

 Codera, along the coast of Estados 

 Carabobo and Falc6n as far as Chi- 

 chiriviche and at the entrance to Lake 

 Maracaibo. At the southern end of 

 this body of water, they are replaced 

 by permanently inundated forests, with 

 Inga, Ficus and Cecropia species. This 

 last type of forest forms a striking 

 feature of our flora and is worth more 

 thorough investigation. 



2. Luxuriant tropical rain-forest. 

 This represents the optimum of vege- 

 tative development in the tropics, but 

 occupies in Venezuela only restricted 



