STUDIES ON RESTORATION ECOLOGY IN THE ATLANTIC FOREST REGION OF BAHIA, BRAZIL

Four hundred years ago the forest of the Atlantic coast of Brazil was approximately 100 million hectares. Today, human settlement and indust rialization have reduced the forest to <15% of its original size. In s outhern Bahia the primary forest is being cleared primarily for agricu ltural reasons. To decrease pressure on the remaining natural forest, it is necessary to increase the productivity of the degraded areas mak ing food, wood and fodder available to the groups exerting pressure on the primary forest. Agroforestry systems and mixed tree plantations m ay represent environmentally sound land use practices for areas with s imilar problems of resource degradation. However, to successfully esta blish a multispecies system that guarantees production and environment al protection, it is necessary to know the relationships among plant s pecies as well as their effects on the soil. The goals of this researc h were to identify indigenous tree species with a positive influence o n soil fertility restoration and to use these data for designing exper imental mixed-tree plantations. The study focused on 20 native species chosen for their ecological significance and their potential economic use. The trees were in pure stands of 36 individuals spaced 2 m by 2 m. All the stands were part of an arboretum at Pau Brazil Ecological S tation (CEPLAC-Porto Seguro, Bahia) and were planted in 1974-75; thus, all the trees were approximately the same age, 14-15 years old, at th e time this research was conducted. Soils for chemical analysis and bu lk density were sampled under the 20 species, a 20-year old capoeira, a mixed-species plantation and the native forest. Soil samples were ta ken beneath five individuals (randomly selected) of each species at fo ur depths (0-5 cm, 5-15 cm, 15-30 cm, 30-45 cm) for measurements of pH , N, P, K, Ca, and Mg. The bulk density was measured with a bulk densi ty corer at 2-6 cm soil depth. Tissue samples (litter and green leaves ) were also collected and analyzed for N, P, K, Ca and Mg. The litter samples were sorted into branches, whole leaves and fragments. Samples from the native forest, the capoeira and the mixed-species plantation were also collected. Positive effects on at least three parameters we re noted under I. affinis, P. pterosperma (N-fixing species): A. psilo phylla, C. echinata, (leguminous, non-N-fixing); E. ovata, L. pisonis, L. hypoleuca (of other families). The mixed plantation had similar so il pH, C, N, Mg, slightly higher P and lower K and Ca than the primary forest: thus, this system apparently represents an intermediate situa tion with respect to the pure stands. Mechanisms related to the observ ed responses are discussed. The results can offer a contribution to th e knowledge of the ecology of the species studied, in conjunction with the existing body of information on soils and nutrient cycling for th e region.