Mangrove Establishment on Artificial Islands: A Case Study

Abstract

During 1953 was a navigation channel for tankers dredged across the sandbanks at the entry to Lake Maracaibo. The dredge spoil was used to establish a series of small islands parallel to one side of the navigation channels. These islands were left alone with the exception of a few houses for occasional usage by local people. They were vegetated by mangrove species from a nearby large mangrove forest. The results of the uncontrolled settlement of mangrove trees until the last 40 years was investigated for all four islands and for the one, we named Isla de Perros. Soil development was studied in order to learn how these small islands developed the soil stratum of the new ecosystem. The effects of the ship traffic could be discovered from aerial photography. At the time of scientific analyses all islands were covered with mangrove type vegetation. Fast changing coastal areas and young volcanic slopes are natural physiographic units adequate to study short term evolution of successional vegetation changes. (Davis 1940) More recently, with the opening of the Florida Atlantic Waterway, as well the maintenance of navigation channels in the Tampa Bay Harbor region at Florida's Gulf of Mexico coast, artificial spoil islands resulting from dredging sea-bottom sediments, have begun to attract attention for planting purposes in order to produce a vegetation cover which could receive and establish permanently water-fowl communities (Lewis and Dunstan 1975). Since observations of natural plant colonization of tropical artificial islands under human undisturbed conditions seems to be lacking, it was tempting to examine the actual established vegetation cover of the initially barren spoil islands which resulted from the dredging of the navigation channel trough the sandy barrier of Lake Maracaibo, executed nearly 50 years ago. The geographical position of this activity is shown in Fig. 11.1. This offers an opportunity to know how colonization and plant succession were able, without any human interference, to differentiate several distinct plant communities. Having recognized that mangrove species are dominant units of the actual vegetation which cover the islands, we draw special attention to study the soil conditions prevailing at their growing sites as expression of the changes which might have some relationship with their existence. 11.2 The Study Site An example of the vegetation cover of the islands is shown on Fig. 11.2 (see also Color Plates page xlix).