Eutrophic overgrowth in the self-organization of tropical wetlands illustrated with a study of swine wastes in rainforest plots

The relationship of plant species diversity to cultural eutrophy in tropica l wetlands was studied in Puerto Rico with experimental plots, a survey of 25 eutrophic sites developing from the wastes of society, and a simulation mini-model. The model is a quantitative hypothesis which contains the mecha nisms to maximize empower (gross production) by reinforcing low diversity, net production overgrowth when resources are in excess, but switches to hig h diversity efficiency and recycle to maximize gross production when excess resources are absent. To study self-organization with eutrophy, six wetlan d plots (3 x 2 m) were seeded with many plant species and treated for five months with pig wastewaters and control plots with groundwater. Vegetation was seeded: (1) with seed bank; (2) with ten species of local rainforest an d wetland trees (60 individuals in each plot); and (3) with weedy species i nvading from fertile surroundings. The fertilized waste plots filled in wit h vegetation in less than half the time (9 weeks) required for the clear wa ter control plots (21 weeks). Vegetative diversity in both waste and contro l plots was maximum (2.73-3.34 bits per individual) shortly before 100% cov er was reached, and then declined with the competitive overgrowth of a few species (mixed grasses and Commelina diffusa). Of the planted seedlings, th ere was little growth, and individuals of only four species survived. Survi val of Andira inermis and Cyrilla racemiflora was 42 and 53%, respectively. Dominants of oligotrophic wetlands (Pterocarpus officinalis and Prestoea m ontana) were displaced. A survey of 25 other wetland sites, receiving high nutrient waters from developments, found low diversity overgrowth, but diff erent species prevailing. Eighty-five species were involved in wetland self -organizational processes and ecological engineering management. Eutrophic wetlands, such as those released from sugar cane closure in Puerto Rico and elsewhere, may be in a state of marshy, arrested succession because there may not be a forest species already adapted for rapid reforestation of the excess nutrient habitat. The study provides evidence of the overgrowth prin ciple as the natural means for ecological engineering of eutrophic interfac es between the current civilization and environment. (C) 2000 Elsevier Scie nce B.V. All rights reserved.