Plant species richness and floristic composition change along a rice-pasture sequence in subsistence farms of Brazilian Amazon, influence on the fallows biodiversity (Benfica, State of Para)

2008

Article référencé dans le Web of Science WOS:000254023100009

Mitja Danielle, Miranda L. D. S., Velasquez Elena, Lavelle Patrick

Agriculture Ecosystems and Environment, 2008, 124 (1-2), p. 72-84 ISSN 0167-8809

Along the Amazonian pioneer front in the Brazilian state of Pari, smallholder farmers manually clear primary rain forest every year to grow rice prior to sowing pastures that they will use for 5-20 years. Species richness and floristic composition of the weedy species were studied in 20 plots along a farming succession, from rice fields, to 1-year-old, 4-8-year-old and over 10-year-old pastures planted to Brachiaria brizantha. In the early phases of the farming cycle reduction in the average plant total species richness in 50 m 2 plots decreased from 67 to 20 species and comprised both woody and herbaceous species. The increase to 41 species further observed in mature pastures was essentially comprised of herbaceous species. Rice fields were characterised by a great floristic heterogeneity which later decreased when they were planted to pastures. PCA of plant communities ordinated plots along a gradient of increasing anthropisation that explained 23.6% of total variance. Species were classified into four ecological groups, which floristic composition and specific richness changed throughout the farming succession. Species richness and density of forest woody species decreased progressively from 32 to 7 species and from 152 to 16 2 individuals per 50 in, and only a few species such as Memora allanmandiflora and Poecilanthe effusa resisted pasture conditions. Pioneer/ secondary woody species of the genera Cecropia and Solanum germinated out of the forest seed bank, and seven species on average were observed in rice fields and 1-year-old pastures. At later stages (>4 years) their respective species richness decreased to three species while their density decreased sharply, from 439 to 41 individuals per 50 m(2). A few forest herbaceous species of the families Marantaceae and Poaceae and the fern species Adiantum argutum, which survived in rice fields (2 species per 50 in 2 on average), almost disappeared in the 4-8-year-old pastures. In the early phase of the intra-farming succession, a rather stable community of six species of secondary herbaceous plants on average was established. Species richness further increased to 16 in the > 10-year-old pastures with addition of species such as Desmodium axillare, Phyllanthus amarus or Cyperus compressus. In accordance with the concept of Initial Floristic Composition, floristic composition at the beginning of the intra-farming succession was determined by the floristic composition of the former forest and by the nature and intensity of the initial disturbance (deforestation and burning). Further changes in species richness, floristic composition and density in the intrafarming succession are driven by the intra-farming management.

Sciences du monde végétal [076] ; Etudes, transformation, conservation du milieu naturel [082]

Fonds IRD [F B010042495]

fdi:010042495