GENERAL CONCLUSIONS. 



Jamaica presents typical insular tropical conditions, with a rainy 

 windward coast, a leeward dry coast , and an intervening cool mountain 

 region. The interesting changes of vegetation between sea-level and 

 4.500 feet (1,370 meters) have been so seriously modified by human 

 interference as to be only imperfectly recognizable. Above this ele- 

 vation, however, is an almost unbroken cover of virgin vegetation, in 

 which the floristie and vegetational changes are relatively slight from 

 4.500 feet to the highest summit, at 7,428 feet (2,205 meters). This 

 undisturbed montane region is characterized by a rainfall of from 105 

 inches (268 cm.) to 168 inches (427 cm.), and by the prevalence of a 

 cloud blanket which is particularly persistent over the windward slopes 

 of the mountains. The prevailing vegetation is a type of rain-forest 

 which possesses an intermingling of tropical and temperate character- 

 istics, and a floristie admixture of genera from the adjacent lowlands 

 and from the north temperate zone. 



Within the rain-forest region the major distinction of climate and 

 vegetation is that which exists between the windward and leeward 

 slopes of the main mountain mass, which lies nearly at right angles 

 to the direction of the trade winds. On both sides of the mountains 

 minor distinctions may be made between the vegetation of ravines, 

 slopes, and ridges. The effects of rain, fog, and wind are modified by 

 the erosion topography in such a manner as to make the Ravines the 

 most hygrophilous habitats, the Ridges the least hygrophilous, and the 

 Slopes intermediate between the two. The forests of the ridges are 

 essentially alike on both windward and leeward slopes, but those of the 

 "Windward Ravines and Leeward Ravines, as well as those of the 

 Windward Slopes and Leeward Slopes, present substantial differences. 

 The most important physical factor concerned in the differentiation 

 of these habitats is atmospheric humidity, although this is, in turn, 

 conditioned by the prevalence of fog. 



The Windward Ravines exhibit most strikingly the characteristics 

 of the rain-forest, some of which are lacking in each of the other habi- 

 tats. No one of the forest types occupying the five habitats may be 

 looked upon as possessing a closer adjustment to its own complex of 

 physical conditions than does any of the others. No one of the types 

 can emerge from its own habitat, and under no possible physiographic 

 change of the region can any one of these habitats come to occupy all, 

 or even a preponderant part, of the region. In other words, there is 

 no means by which it might be possible to fix upon any one of the five 

 types as representing the so-called " climax" forest of the Jamaican 

 montane region. 



106 



