Grasslands: Productivity and Biomass

Abstract

Grassland is one of the most widespread vegetation types worldwide and plays a prominent role in ecological security and human development. Three important factors have been responsible for the evolution and maintenance of the grassland ecosystem: drought, fire and grazing. The naturally occurring grasslands, primarily determined by climate, occur in areas where growth of forests is prevented by non-availability of sufficient soil water. In addition to the climatically determined natural grasslands, successional grasslands are maintained by removal of original forest vegetation as a consequence of grazing, mowing or burning. For their importance in ecological productivity, studies of their biomass and ecological productivity is very important.    A number of different methods and models have been used to estimate their biomass production and productivity. Every method has its own merits and demerits. Even though alternatives to the conventional harvesting methods have been devised, the conventional harvesting methods for ecological productivity are still in vogue. The research attributes the role of precipitation and temperature in regulating productivity in grasslands. Probably because of more favourable environmental conditions throughout the year, tropical grasslands are more productive on an annual basis than their other counterparts. Similarly different species in a grassland may respond differently to the amount, occasions and type of precipitation. The plant biomass and productivity in grasslands is not affected only by present year precipitation but also by previous year precipitation amount and pattern. The productivity of C₃-species and C₄ species also respond differently to mean annual temperature and mean annual precipitation. Different types of biotic stresses also affect plant biomass and primary productivity the most important biotic stress among them is grazing. Although heavy grazing and no grazing in general decreases productivity, moderate grazing has positive effects on productivity. Aboveground and below ground biomass is also affected by both abiotic and biotic factors. The outcome of different ecological factors result in the amount and ratio of aboveground and belowground (living and dead biomass)