[Quantitative ecology of young stages of the forest reconstitution in the Equatorial region [Kongolo, Island Masako, Zaire]]

Plant growth has been studied in consideration of traditional cultural practice in Kisangani region (Zaire). Plant communities dynamic was studied from phytosociological releves in consideration of floristic composition and synecological structure of the species at different stages of the forest regrowth. The releves were analysed using ecological spectra (biological and ecosociological). The therophytes were the most dominant plants in the earliest stages. The preforested and forested fallows were characterized by a preponderance of phanerophytae (particularly mesophanerophytae) and decreasing of other biological forms especially therophytae. Fallow dynamic was remarkable by a rapid regrowth and a predominance of herbaceous species which declined six months after deforestation. Correlatively of their decrease, typical preforested and forested species became dominant. In the shrub layer, various megageophytae (Commelinaceae, Costaceae, Marantaceae and Zingiberaceae) were developed and declined as the woody plants became higher. The phytosociological analysis allowed us to determine five stages of the forest regrowth which correspond to four ecosociological groups. Each group succeeded to another by a progressive replacement of long-lived species. Plant biomass and soil analysis were studied during six year period permanent plots and in a ten year old forested fallow. For each stage, the mineral nutrients immobilization was evaluated from poly elements content analysis. Plant biomass increased with length of the fallow period. After three months, herbaceaous vegetation produced 1,7 ton per hectare (dry matter) which reached 103,6 ton per hectare (dry matter) for the ten year forested fallow. This last fallow was essentially composed of woody plants. The changes of plant biomass according to the plot treatment were correlated to tree density. The sequence of mineral nutrient stock remained the same despite the plot treatments. The differences between plot treatments were only related to the importance of mineral nutrient immobilization which depended upon the plant biomass and mineral nutrient content in plant material. The exchangeable K, Ca, Mg and assimilable P in the 20 cm top layer of the soil were 3 to 6 times less than that in plant biomass during the fallow period. However, total N in the same layer of the soil was significantly higher than that accumulated in the plant biomass. Total C in plant increased from 0,8 ton per hectare at 3 months to 50 ton per hectare at ten year