Testing the Ecosystem Productivity- Diversity Hypothesis in a Grassland

Abstract

Globally, the academic debate about the relationship between species diversity and ecosystem productivity has been widely contested. While some researchers support the positive relationship between ecosystem productivity and diversity, others propose the reverse. However, mechanisms that play a role in this relationship remain unclear. As such a study was conducted in Lilongwe plain, in Malawi to test the theory of ecosystem productivity and diversity in a grassland ecosystem to make a humble contribution to this debate. Methodologically, five transects of 25metres each, were systematically drawn across the area. Each transect had 14 quadrats that were randomly placed at a distance of 10 meters apart. The data sets (moisture content, distribution and composition of plant species were collected in 5 transects located in two contrasting areas of dry and waterlogging conditions. Alpha diversity was computed to determine variations in species diversity between dry and the water logged areas. The results show that moisture content and species composition were the main productivity influencing factors with P-values <0.05. Results further show that there is indeed a relationship between productivity and diversity which was affected by variations in the availability of water, legume species that initiates nitrogen fixation, and nature of the mixture of the grass stands within the study area. Despite few numbers of species in areas of high water concentration, the results show that the biomass production was considerably high. The higher diversity in the upper and middle areas of the land indicates more species that survive as well as facilitate and complement each other.

Such areas support the concept of complementarity which result from interspecific differences in resource requirements and that of facilitation which result from certain species helping or allowing other species to grow by modifying the environment in a way that is favorable to co-occurring species. The findings suggest that the correlation between productivity and diversity cannot be disputed. But the specifics as to when and how this relationship exhibits need to be clearly understood since this relationship is influenced by factors such as species composition as well as conditions in that particular area where the species exist, (in this case the grassland). Perhaps in this study the relationship was influenced by the presence of water in some areas which exhibited higher biomass but little diversity, as well as the presence of leguminous grasses that fix nitrogen and benefits surrounding species hence increasing the biomass as well.