Biological communities: The historical factor in plant communities
The history of any botanical community is often as important in explaining its composition as are the environmental factors which form the normal study of ecology So the ecologist will need to consider problems of plant-distribution, just as the plant-geographer must take into account the ecological requirements of the species.
In a study of a collection of plants made in a rain-forest in central Colombia it became evident that the community could be broken down into a number of geographical elements. Some plants spread far into the Amazon forest, some were confined to the Andean slopes, some ranged north into Central America, and so on.
The most interesting element was a small group of plants characteristic of certain abrupt and isolated mountain systems which stretch across the northern part of South America. They separate the water-systems of the Orinoco and the Amazon, and lie in the Guianas, Venezuela and Colombia. These mountains have been found to have certain floristic resemblances, and as they are all eroded remnants of a former continuous plateau, the attractive theory has been suggested that their floras resemble each other because they are residues of a former widespread plateau flora, now immeasurably reduced.