SOIL FAUNA DENSITIES AND FLUCTUATIONS IN CENTRAL AMAZONIAN FORESTS AND POLYCULTURES AS AFFECTED BY THE EL NIÑO AND LA NIÑA EVENTS IN THE YEARS 1997 – 1999
Werner Hanagarth1, *Hubert Höfer1, Christopher Martius2, Marcos V.B. Garcia3 and Jörg Römbke4
1Staatliches Museum für Naturkunde, Postfach 11364, D-63013 Karlsruhe, Germany, 2Center for Development Research (ZEF), Walter-Flex-Str. 3, D-53113, Bonn, Germany, 3Embrapa Amazônia Ocidental, Caixa Postal 319, Manaus-AM, Brazil. 4ECT Ökotoxicologie GmbH, Böttgerstr. 2-14, D-655439, Flörsheim, Germany.
*Corresponding author. email: hhoefer_smnk@compuserve.com
Accepted in January 2004.
Abstract
A survey of the soil meso- and macrofauna in three different forest systems (a primary forest and a secondary forest site as well as two polyculture plantation sites) in central Amazonia was carried out between July 1997 and March 1999. Main interest of the study was to reveal the presence, abundance and relative importance of functional groups of the soil fauna in decomposition and nutrient cycling processes in polyculture plantations. Here we describe and analyze the abundance of the meso- and macrofauna in relation with litter quantity and its dependence on regional climate conditions as well as site-specific microclimate. Mean mesofauna density over 8 sampling events in all three forest systems ranged between 13-17,000 ind./m² at the lower end when sampled in the dry seasons and 30-40,000 ind./m² at the higher end when sampled in rainy seasons. Mean macrofauna densities ranged between 2,100 Ind./m² during the La Nina dry season in the polycultures and 9,200 Ind./m² during the El Nino dry season in the primary forest. The assessment of the macrofauna in the plantations showed a substitution of taxa and functional groups dominating in the primary forest. Social insects (ants and termites) were more abundant in the primary forest than in the secondary forest and even less abundant in the polyculture plantations. In contrast, some primary decomposers (diplopods and isopods) were more abundant in the polycultures than in the forests. Litter quantity was an important factor determining abundance of litter fauna, but the association was different for different plots and influenced by the temporal variation of rainfall. The strong rainfall deficits during the El Niño event had no negative effects on the soil macrofauna. Most arthropod groups had higher abundances during the predominance of El Niño, than in the following normal and La Niña events. Thus, the soil macrofauna responded differently from the soil mesofauna. Both, macrofauna and mesofauna migrated from the litter layer to the soil layer during El Niño.