Estructura, composición y variabilidad del bosque subandino xérico en un sector del Valle del río Tuichi, Anmi Madidi, La Paz (Bolivia)

Abstract

Se evaluaron 1.3 has. de bosque subandino xerico en el valle del Tuichi donde se midieron todas las lenosas con DAP > 2.5 cm en parcelas de 0.1 has. Se registraron 4709 tallos en total, con un promedio de 362.2± 132.3/0.1 ha. El promedio del area basal fue de 2.9± 1.1 m2/0.1 ha. Se encontraron 171 especies y 50 familias, con promedios de 48±7.5 especies y 24.8±3.8 familias por parcela. Las especies de mayor importancia ecologica (IVI) fueron Phyllostylon rhamnoides, Anadenanthera colubrina y Trichilia catigua; las familias con mayor IVIF fueron Fabaceae, Meliaceae y Ulmaceae. El Analisis de Componentes Principales diferencio dos grupos de parcelas o comunidades: una comunidad de cimas y laderas caracterizada por Zanthoxylum fagara, Astronium urundeuva y Erythrina amazonica; y otra comunidad de fondos de valle y terrazas caracterizada por Chrysophyllum gonocarpum, Randia armata y Gallesia integrifolia. Biogeograficamente predominan especies de bosques estacionalmente secos del arco pleistocenico, reforzando la teoria de la existencia durante el Pleistoceno de una formacion de bosques secos mucho mas extensa que la actual; le siguen en orden de importancia elementos de bosques humedos de tierras bajas y por ultimo elementos andinos que concentran los endemismos y caracterizan a esta formacion. Palabras claves: Bosque seco subandino Madidi, estructura, composicion, variabilidad, biogeografia. ABSTRACT We present detailed information on structure and floristic composition of the xeric subandean forest in a sector of the Tuichi valley, in the Madidi Natural Area of Integrated Management, La Paz-Bolivia. We evaluated 1.3 has. of forest where we measured all the woody plants with DBH > 2.5 cm, in plots of 0.1 ha. A total of 4709 stems with means of 362.2± 132.3/0.1 ha were recorded. The total basal area was of 37.7 m2 with means of 2.9±1.1 m2/0.1 ha (S.D.). We recorded 171 species in 50 families, with means of 48±7.5 species and 24.8±3.8 families per plot. The species of greatest ecological importance (IVI) were Phyllostylon rhamnoides, Anadenanthera colubrina and Trichilia catigua; the families with greatest IVIF were Fabaceae, Meliaceae and Ulmaceae. A Principal Component Analysis distinguished two groups of plots or plant communities: a community found on top and slopes of ridges characterized by Zanthoxylum fagara, Astronium urundeuva and Erythrina amazonica; and the other a community found in the valley bottoms and terraces was characterized by Chrysophyllum gonocarpum, Randia armata and Gallesia integrifolia. Biogeographycally predominates species of seasonally dry forests of the pleistocenic arc, reinforcing the theory of the existence during the Pleistocene of one formacion of dry forests much more extensive that in the present; they follow in importance order elements of humid lowland forests and finally Andean elements that concentrate the endemism and characterize this formation. Key words: Madidi subandean dry forest, structure, composition, variability, biogeography.