Distribution patterns of the litter macrofauna in agroforestry and monoculture plantations in central Amazonia as affected by plant species and management

Abstract

Within heterogeneous land-use systems such as agroforestry or mixed tree crop plantations, the different morphological and physiological characteristics of the plants, together with their species-specific management, lead to a mosaic of different living conditions for the litter fauna. This may, in turn, influence the processes of decomposition and nutrient cycling and, thus, the growth-conditions of the plants. We studied the effect of different plant species on the litter macrofauna by collecting macro-invertebrates in the litter layer of an agroforestry system composed of four regionally important tree crop species in central Amazonia: cupuaçu ( Theobroma grandiflorum), annatto ( Bixa orellana), Brazil nut ( Bertholletia excelsa) and peach palm ( Bactris gasipaes), with the leguminous cover crop Pueraria phaseoloides and spontaneous grasses as soil cover. The agroforestry system was studied at two fertilisation levels and was compared with a peach palm monoculture. We found invertebrates belonging to 18 orders and 44 families. The number of fauna individuals per unit area differed significantly between plant species within the agroforestry system. Both the number of individuals and the faunal biomass increased linearly with litter dry matter per unit area. The Shannon–Wiener index of family diversity showed a non-linear increase with increasing sampling area and litter mass in the samples, approaching saturation values between 2 and 2.5. The highest faunal abundance and diversity was found in the litter of the peach palm monoculture, apparently due to the stable and protected habitat provided by the fleshy offshoot remains from the palm harvests. The two fertiliser levels only differed with respect to two invertebrate groups, snails and isopods. The results indicate that the creation of a litter and/or mulch layer of at least 3 Mg ha −1, but preferably 6 Mg ha −1 and the association of tree and cover crop species whose litter has a favourable effect on the fauna with species whose litter has a less favourable effect are suitable management tools for the conservation of an abundant and diverse litter fauna in plantations and agroforestry systems of the humid tropics.