Effects of exclosure on aboveground biomass, vegetation constitution, and midday gross primary productivity in semi-arid Mongolian steppe

Abstract

We examined the effects of grazing on aboveground biomass (AGB), vegetation constitution, and gross primary productivity (GPP) at midday in midsummer on a Mongolian steppe with mixed vegetation consisting of C3 and C4 plants. A grazed area (GA) and a nongrazed area (NGA) created by an exclosure were established in 2002 on land with a history of conventional grazing management. AGB of the mixed C3-C4 vegetation was determined in the GA and NGA from 2003 to 2006. Nongrazing resulted in increased AGB and a decreased ratio of C4 AGB to total AGB. In 2003 and 2006 a dynamic closed-chamber method was used to measure midday GPP; there was no significant difference between the GA and NGA in either year. Partitioning analysis of midday GPP to C3 and C4 photosynthesis indicated that exclosure exerted little influence on the midday GPP in midsummer, because the enhancement of GPP by increased AGB was offset by the reduced AGB of C4 plants.