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Comparative analysis of eight neotropical savanna ecosystems : production-decomposition indexes

Breymeyer A.

Polish Journal of Ecology

2001

Vol. 49, nr 4

339-358

Comparative studies of the functioning of eight neotropical savannas were conducted in Venezuela and Panama. Savannas were classified in the following 4 types of increasing productivity: Trachypogon savanna, "Bajio" savanna, Paspalum savanna and Hyparrhenia savanna. Each savanna type was reprezented by sites ungrazed orgrazed by cows. All stands, except for the flooded "Bajio" were burnt at the end of the rainy season. The rates of two ecosystem processes were measured: productivity (NPP) and decomposition. The index of productivity was the maximum biomass ofABVG (above ground biomass) and BLG (below ground mass of roots); this was measured at the end of the rainy season just before the fire. Decomposition rate was evalued using litterbags with local litter or filter paper exposed in different layers of savannas. ABVG production of biomass is highest in non-grazed Hyparrhenia savanna, where it reaches 19-20 g d.w.m^-2 daily and 2850-2950 g d.w.m^-2 in the rainy season. This is a very high figure rarely noted in grasslands. The lowest productivity -544 g d.w2.m^-2 ABVG in the rainy seasons - was noted in Trachypogon savannas. Roots constitute a small part of savanna biomass: 14-25% in Hyparrhenia savanna, and 6-45% in Venezuelan savannas. The biomas of roots is concentrated in the 0-10 cm layer: 86-90% in Hyparrhenia, 40-72% in Venezuelan savannas. The decomposition of litter evalued for 6 Venezuelan savannas and calculated for the wet season ranges from 180 to 1126 g d.w.^-2. Higher decomposition occur in stands with higher productivity. To the new findings can be assigned the results of comparative measures of decomposition on four levels (from soil to 40 cm above the ground surface). In the Hyparrhenia stand as much as 52% of decomposition takes place in the standing plants. The OM budget calculations suggest that all 8 stands are characterized by an accumulation of organic matter; however, decomposition rate is underestimated as the fraction of OM decomposed in standing plants is not considered.