Recultivation saves the Amazonian rain forest
Terra firme - the dry land - is what the Brazilians call those parts of the Amazon region which are not submerged by the flooding rivers and are mainly covered by evergreen tropical forest. These largely virgin rainforests have been experiencing intense pressure from many parties interested in land use, and devastating processes (farming, forestry systems as weIl as mining) have already been set in motion at many sites.
The process generally starts with new roads or other transport paths cut into the forest. They serve as a point of entry for a continuously growing number of settlers who want to open up new living space and cut down the vegetation. Usable timber may be taken out but the major fraction of the wood is bumed.
The areas cleared, used for agriculture or stock raising, are usually exhausted after three or four years and the yields become progressively smaller. The owners then abandon these fields and clear a further tract of forest as areplacement so that the destruction is spread further.
In those areas of the Amazon region, around large cities like Manaus, the landscape is already mainly characterised by anthropogenic influences. The original forest has disappeared except for small, unconnected residual areas. A large number of people live in this region today and their economic needs must be included in any proposed solutions if the latter are to have any chance of success. Due to the rapid decline of fertility in the soils of former agricultural areas, which were abandoned because of economic reasons, fallow can be found around all urban centers like Manaus.
Within the bilateral German- Brazilian program on Studies of Human Impacts on Forests and Floodplains in the Tropics (SHIFT), in the project ENV 23 ("Recultivation", see Google Earth 2° 52'53.34'' S ; 59° 50'40.09'' W), these fallow lying areas were re-cultivated in order to identify biotic and abiotic stabilizing factors for agro-ecologically equilibrated production systems. Furthermore, a viable method to install a sustainable plantation with minimised losses in the starting phase had to be demonstrated as a concrete, environmentally friendly option for long lasting agricultural use of tropical areas.
Summary of experimental results
The experimental polyculture systems installed as different planting systems with increasing complexity resulted in sustainable agriculture on degraded sites. The experimental area has been available to study several ecological and economical aspects for a variety of research groups of in total four SHIFT projects. Most important in the early installation phase of the experimental system was the consideration of the mycorrhizal technology and its demands to reach a quick ecological equilibration and positive economic balance. Fertilizer level, plant combination and interactions between plants were assessed qualitatively and quantitatively over a period of more than eight years. Compared to the monoculture, polyculture was more stable against pests and diseases of the crops. Inoculation with arbuscular mycorrhiza decreased plant loss after planting. One year after planting, the population of mycorrhizal spores on the experimental sites was very heterogeneous. The change of AMF spore type composition could be used as indicator for the ecological stabilization process. The externally produced and then introduced Glomus etunicatum inoculum was successfully substituted by other autochtonous fungi. Already in the transition phase, before a sustainable production phase was reached, the yields of Carica papaya and Manihot esculenta were commercially relevant. Four years after the installation, the system reached its production phase which was mainly based on Bactris gasipaes, Theobroma grandiflorum and Bixa orellana. Mycorrhizal treatment partially revealed higher yields, better growth and disease tolerance of crops. The vegetation was assessed in the experimental sites as well as in secondary and primary forest. The spontaneously growing secondary vegetation could be used as an indicator system for the assessment of prior land use and site quality. An extensive list of species was compiled. During the experimental period, the polyculture systems were proved to have a stable production due to adapted management procedures like mulching and methods of precision farming. The integrated plant management system could be recommended for the regional agriculture, particularly with regard to agro-ecological aspects (soil erosion, disease susceptibility, nutrient storage). Besides perennial crops, the planting systems provided potential farmers with annual crops for their subsistence. Due to the complexity of the planting systems, small holders will need a more thorough training than for the conventional subsistence systems.
Agro-ecology - Agroforestry - Mixed Cropping Systems - Coordination - Fund raising