Impact of ecological factors on the regeneration of mangroves in the Cienaga Grande de Santa Marta, Colombia

In the Cienaga Grande de Santa Marta, a brackish lagoon system on the Carib bean coast of Colombia, human-induced changes in the hydrological system ca used hypersalinisation of the soils. As a result, 30 000 ha of originally 5 1 000 ha of the mangrove forests growing in the lagoon's flood plain died. Presently, efforts are being made to reestablish the original hydrological system. Reforestation of the bare areas is planned with the three dominatin g mangrove species Avicennia germinans, Laguncularia racemosa and Rhizophor a mangle. The objective of the project presented here is to identify the re generation patterns in the study area. Experiments under controlled conditi ons and measurements at bare and forested sites carried out from 1994 to 19 96 showed that regeneration is possible. However, as the bare areas are lar ge and presently very few or no propagules arrive naturally, regeneration w ill be slow. Therefore, reforestation is recommended to accelerate the proc ess. In the forests, the seedling growth is mainly controlled by changes in salinity and the mortality by seasonal flooding, while in the bare areas, regeneration is aggravated by extremely high salinities, high soil temperat ures and dessication of the top soil layers. The establishment of the small A. germinans and L. racemosa propagules is especially difficult, because t hey cannot establish themselves in flooded soils and in direct sunlight the y dry out rapidly. The seedlings of both species are also very sensitive to changes in water level, wind, waves, temperatures exceeding 45 degrees C a nd dry soils. In A. germinans, phytophagous insects affect the chances for survival also. Therefore, mortality in both species is extremely high. R. m angle is much more resistant to most detrimental factors observed with the exception of high salinities. However, there is one favourable factor at th e open sites. When sufficient water is present and salinities as well as te mperatures are low enough, the high light availability increases growth rat es and survival.