FOREST FORMATIONS OF THE ISTHMUS OF PANAMA 77 



ascend the slopes. The trade-wind reaches its maximal intensity when 

 the sun is farthest south of the Equator, in March, and is prevailing 

 on the Isthmus during about nine out of twelve months, making its 

 influence felt clear across the country. The monsoon, on the other 

 hand, is very irregular, at least in the central and western sections of 

 the Pacific coast, blowing with some constancy only from May to 

 October and not strong enough, as a rule, to modify the climatic con- 

 ditions on the Atlantic watershed. 



Thus the trade-wind practically causes abundant and perennial rain- 

 fall on the northern seaboard of the country, but having lost most of 

 its humidity in the ascent to the summit of the Continental Divide, it 

 acts in the opposite way, that is to say, as a drought-producing wind, 

 on the southern slope, with the exception of a narrow fringe of the 

 upper belt. During the predominance of the monsoon, however, such 

 effect of the trade-wind on the Pacific slope is overcome, and for nearly 

 six months this slope is favored with almost daily rainfall. At the 

 southernmost end of the country, in Darien, the monsoon blows stronger 

 and with greater regularity, causing again abundant perennial rainfall, 

 interrupted, however, by two short dry spells, in March-April and Sep- 

 tember-October. This district is adjacent with the Colombian Choco. 

 which shows the heaviest rainfall of the western continent. 



To sum up, the climate of the Atlantic watershed and of Darien is 

 characterized by the rainfall being distributed on the whole length of 

 the year, while that of the central and western sections of the Pacific 

 slope shows two well-marked periods — a dry season, lasting from 

 December to April, and a wet season, extending between May and 

 November. 



Panama City has i8o days of annual rainfall ; Colon, 246 days. The 

 latter, however, is a low average, because of the exceptional location of 

 Colon, in front of the great gap in the Continental Divide. Port Limon, 

 in Costa Rica, has 304 days. The annual amount of rainfall is, of 

 course, much larger on the Atlantic side: Colon has an average of 3.19 

 m, (129.4 inches), Panama only 1.80 m. (70.9 inches). No data are 

 available as yet for Darien. The amount of rainfall decreases as the 

 altitude increases: the dryest point in Panama is probably the summit 

 of the Chiriqui Volcano, situated to the south of the Continental Divide. 



These peculiarities in the regime of the winds and of the rainfall are 

 sufficient to explain the presence of a continuous forest belt along the 

 Atlantic seaboard, as well as in Darien and on both sides of the crest 

 of the Continental Divide, and of savannas and park-like formations in 

 the remaining part of the Pacific slope. 



