NATURAL AREAS AND REGIONS 



633 



uniformity of the forest makes inadvis- 

 able its separate consideration upon 

 each cordillera. However, the wetter 

 conditions prevalent on the western 

 slope of the Western Cordillera and 

 upon the eastern slope of the Eastern 

 Cordillera have produced biotas differ- 

 ent from that of the sheltered inter- 

 Andean slopes. Everywhere, also, have 

 geographic remoteness and especially 

 isolation of upland areas resulted in 

 diversity of the composition of the 

 fauna and flora. The supreme illustra- 

 tion of isolation is the life on the Santa 

 Marta mountains. 



Much more important for considera- 

 tion is the modification of life caused 

 uniformly on all mountain-systems by 

 increasing elevation and resultant cooler 

 temperatures. Thus we may distinguish 

 a forest of the lower and warmer, and a 

 forest of the upper and cooler, mountain- 

 slopes two types of forest that show 

 very important differences in com- 

 position. 



Subtropical Evergreen Forest. The 

 lower mountain-forest is essentially 

 similar to the evergreen lowland 

 forests already discussed. The hard- 

 wood trees belong to the same families, 

 and palms and conspicuous lianas also 

 occur. Even more prominent than in 

 the lowlands is the occurrence of ferns 

 of many types, and tree-ferns here 

 become frequent and characteristic. 

 The trees average lower than in the 

 lowland forest, and their branches 

 spread from shorter trunks. The chief 

 distinguishing feature of the lower 

 mountain-forest is the great abundance 

 and wide variety of epiphytes, con- 

 stituting a remarkable aerial world of 

 life. Epiphytic ferns and mosses 

 abound, and of the various groups of 

 flowering plants with epiphytic re- 

 presentatives the chief place is held 

 by the two families most highly spe- 

 cialized for this mode of existence, the 

 Bromeliaceae and the Orchidaceae. 

 There is considerable bloom in this 

 forest and consequently, as compared 

 with the lowland, a greater number of 

 pollinating insects and birds. Among 



the conspicuous flowers are, beside the 

 two families of epiphytes named, ter- 

 restrial species of Gesneriaceae (red, 

 yellow, white or violet), Lobeliaceae 

 (red, pink or green) and the Ericaceae 

 (red, white or orange). Significant 

 through both lower and upper mountain- 

 forests are the number of tubular red 

 flowers, usually yellow within, doubtless 

 adapted for pollination by humming- 

 birds, a form of flower shown in many 

 families, e.g., Lobeliaceae, Rubiaceae, 

 Gesneriaceae, Bignoniaceae, Logania- 

 ceae, Ericaceae, Onagraceae, Loran- 

 thaceae, and even Orchidaceae. 



A wetter phase of the lower moun- 

 tain-forest, which is developed on 

 slopes especially exposed to moisture- 

 laden winds, is remarkable for the 

 extensive and deep growth of mosses, 

 both terrestrial and epiphytic, for 

 the predominance of ferns, Carludovicas 

 and like foliage plants, and for the 

 scarcity of bloom. 



A drier phase of the lower mountain- 

 forest, which is encountered chiefly 

 where the ascent to forest is made from 

 open arid slopes, contains slight diver- 

 sity in trees and few if any epiphytes. 

 The growth of trees is open, and the 

 forest will frequently consist of nearly 

 pure groves of the evergreen Humboldt 

 Oak. Between the lowland prairie and 

 such groves is usually a belt of xerophy- 

 tic bushes. 



This lower mountain-forest and the 

 occasional open areas occurring at 

 the same altitude have been denomi- 

 nated the "Subtropical Zone" in Dr. 

 Chapman's study of Colombian bird- 

 life. The chief families of birds are 

 (1) Tanagridae, (2) Tyrannidae, (3) 

 Trochilidae, (4) Dendrocalaptidae, (5) 

 Fringillidae. 



This zone ' 'includes most of the larger 

 mammals of the lowland forest and some 

 of the smaller ones or, in many cases, 

 representative subspecies." 



Subalpine Evergreen Forest. The up- 

 per mountain-forest is yet lower in 

 height than the forest just considered 

 and shows a decidedly greater adapta- 

 tion to a cool environment. It is less 



