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partially submerged mud banks and shoals, that the growth of young plants fixes the shoal, and 

 that the later development of prop roots of the plant is instrumental in building the shoal into 

 an island, which eventually is attached to the mainland by alluviation. It is true that the prop 

 roots of mature mangrove probably serve to catch fine particles in water and thus aid in deposi- 

 tion. However, along the Colombian coast and elsewhere, ^ it is observed that land must be 

 entirely emerged before it is colonized by plants, that the first colonizers are not Rhizophora, 

 but black mangrove (Avicennia), and that Rhizophora will not establish or even maintain itself 

 except in quiet saline to brackish water in protected bays or along coastlines protected from 

 wave action by offshore bars or shoals. Strong wave action appears to preclude the develop- 

 ment of mangrove and destroys existing stands. Constant shifting or destruction of mud shoals 

 and of offshore mud or sand bars causes continual change of locale of strong wave action along 

 mangrove-bordered bays. At such points wave action immediately begins to erode the muck 

 and underlying peat-like material which supports the mangrove, eventually killing extensive 

 areas of Rhizophora and Avicennia forest. 



The Pacific coast of Colombia contains but a small fraction of the world's mangrove 

 swamp; nevertheless, it affords an excellent example of the physical and related travel and 

 subsistence conditions to be expected within such a type of littoral. Detailed comparisons with 

 other mangrove areas of the tropics would doubtless reveal interesting and valuable facts. Un- 

 fortunately, however, although numerous botanical and ecological studies of mangrove swamps 

 have been made for small areas, the world distribution of that feature has never been adequately 

 mapped, and the world cultural and physical geography of mangrove swamps remains to be 

 studied. 



SUMMARY OF DISCUSSION 



Some comments were made on the ability of mangroves to pioneer in areas protected 

 from strong wave action. The black mangrove (Avicennia) appears to be much more tolerant 

 of high temperatures than the red mangrove (Rhizophora) and may be more tolerant of salt. 

 Consequently it is found nearer the sea. In some areas, as along the Gulf Coast of Florida 

 where there is little sediment in the water, the prop roots of the mangrove are not too effective 

 in building shoals. 



"See, for example, Freyberg, G. von, "Zerstorung und Sedimentation an der Mangrovekiiste 

 Brasiliens," Leopoldina , Vol. 6, pp. 69-117, 1930. 



