Water supply of Swietenia macrophylla King and Carapa guianensis Aubl. in three plantation systems

The following investigations were initiated by the increasing demand for the development of sustainable landuse systems in the Central Amazon, including high quality timber production. Mixed plantations are able to reduce the strong exploitation of high quality timber trees in primary forests in this region. In order to develop sustainable plantation systems, knowledge on the site demands of the tree species is necessary. Especially the seasonal variation of the water supply of the Central Amazon influences tree growth and wood formation in plantation systems. Therefore, the water supply of the important commercial timber trees Swietenia macrophylla King and Carapa guianensis Aubl. (Meliaceae) was studied in three different plantation systems (monoculture system, mixed culture system, enrichment system established in 1992/ 1993) near Manaus, Brazil. Seven trees each of Swietenia macrophylla King and Carapa guianensis Aubl. were selected to study the xylem water conducting system expressed in terms of the morphology and anatomy of the leaves, the stem and the roots of 6-year-old plantation-grown trees. Furthermore, the permeability of the stem xylem was studied. The relationship between the soil water tension, studied by tensiometer measurements, and the water uptake and the water release of plantation-grown Swietenia macrophylla King and Carapa guianensis Aubl. was investigated by xylem runthrough measurements carried out by the Granier method. The water balance of the plantations was quantified by evaporation, transpiration/ xylem flux measurements, as well as by the calculation of the water flux in the soil (Cl-method).The morphological and anatomical investigations revealed a strong seasonal variation of the fine root biomass and the leaf area of Swietenia trees, with a strong reduction during the drier season from July until November. In contrast to that, only slight differences were found for the root biomass and the leaf area of Carapa trees. Consequently to this, the relationship of water uptake and water release of the two species showed significant differences in relationship to the soil water content. Even in short-time periods with a reduced soil water supply, a water deficiency was detected for Swietenia, whereas the water reservoirs of Carapa could be completely refilled during the night, even during dry periods. The spontaneous vegetation of the plantation systems, and with that the plantation management, had a strong influence on the water supply of the plantation-grown trees. In 6-year-old monoculture systems, evaporation and water percolation through the solum were of main importance for the water balance of the plantations, whereas in the mixed plantation system and the enrichment system 40 to 70% of the water output were due to transpiration.