148 



THE ANDES OF SOUTHERN PERU 



by the types of forest growth, the heaviest rains occur around 

 8,000 feet. It is between these elevations that the densest part 

 of the Peruvian montana (forest) is found. The cold timber line 

 is at 10,500 feet with exceptional extensions of a few species to 



ZONEOFLIGHT RAIN AND LOCALSNOW ZONE OF MAXIMUM RAINFALL 

 DRY AND WET SEASONS SHARPLY iONE WELL-MARKED SHORT DRY 

 MARKED AND EQUALIN LENGTH JSEASON 



ZONE OF MODERATE RAINFALL 

 ONE WELL-MARKED LONG DRY 

 SEASON 



Fig. 93A — Cloud types and rainfall belts on the eastern border of the Peruvian Andes 

 in the dry season, southern winter. The zone of maximum rainfall extends approxi- 

 mately from 4,000 to 10,000 feet elevation. 



12,500 feet. In basins or deep secluded valleys near the moun- 

 tain border, a dry timber line occurs at 3,000 feet with many varia- 

 tions in elevation due to the variable declivity and exposure of the 

 slopes and degree of seclusion of the valleys. Elsewhere, the 



TRADES FEEBLER ; LOCAL INFLU- : TRADES REINFORCED BY STRONG UP-; 

 ENCES STRONG j VALLEY WINOS BY DAY AND NEUTRALj 



| IZED BY MODERATE DOWN-VALLEYi 

 NDS BY NIGHT 



NORMAL TRADES 





Fig. 93B — Cloud types and rainfall belts on the eastern border of the Peruvian 

 Andes in the wet season, southern summer. 



mountain forest passes without a break into the plains forest with 

 change in type but with little change in density. The procumbent 

 and suppressed trees of the cold timber line in regions of heavy 

 winter snows are here absent, for the snows rarely reach below 

 14,000 feet and even at that elevation they are only light and tem- 

 porary. The line of perpetual snow is at 15,000 feet. This 

 permanent gap of several thousand feet vertical elevation between 

 the zone of snow and the zone of forest permits the full extension 

 of many pioneer forest species, which is to say, there is an irregu 7 



