Along the west coast of South America mangroves are found only outside the area influenced by the cold Peruvian Current. At 6 ° S (near 'Cerro Illescas') the current turns west to the open sea in the direction of the Galapagos Islands. Dense mangrove vegetation with a tree height up to 15 m occurs only north of 3 ° 35' S from the delta of the river Tumbes (Peru). At 3 ° 44' S some small individuals of Rhizophora and at 5 ° 30' S a small stand of Avicennia can be found. In the transition zone between 3 ° 35' and 6 ° S no mangrove forest occurs. The reasons for the lack of mangal in the transition zone are:
(1) Evapotranspiration and atmospheric humidity show significant differences between the mangrove region and the transition zone. In this zone soil conditions like salinity, water and organic matter content and the geological structure can also be considered as inhibiting mangrove growth.
(2) Topographic conditions in this zone are not suitable for mangal and the lack of a regular annual flow from rivers provides a sharp limit for the existence of mangal in the delta of the river Tumbes. Nevertheless, cultivation of mangrove species south of the mangrove region is possible and seems promising.