Composição e estrutura da comunidade herbácea de sub-bosque e sua distribuição em relação a fatores ambientais na FLONA de Caxiuanã, Amazônia Oriental.

Abstract

The herbaceous plants are an important component of the understory of tropical forests, but have few studies addressed. This study described the composition and structure of the herb community in addition to relate its abundance and distribution with local environmental variables at the Caxiuanã National Forest, Eastern Amazônia. Thirty transects of 2 x 100 m (0.6 ha in total) were scheduled and followed, in its largest axis, topographic contour to minimize variations ofthe soil. Ali ground herbs taller than five centimeters were counted and morphoidentified. Low trunk epiphytic herbs were sampled in the same plots in ali the phorophytes that possessed such plants to a height of eight meters. Identification of the material collected was performed with the aid of specific literature and compared with herbarium specimens of herbarium MG. In total were identified 36 terrestrial species (5421 individuais) and 37 epiphytic morphospecies (1093 individuais in 741 phorophytes). Due to the large number of individuais included in the epiphytic inventory were in juvenile stages or without reproductive structures, only 28 morphospecies (72%) could be identified to the most specific taxonomic levei. Marantaceae was the family most representative in the understory. The three most important species of terrestrial community were Ischnosiphon martianus, Calathea aherrans and Ischnosiphon gracilis which together accounted for more than 50% of ali individuais. The distribution of terrestrial species was similar for both gradients of soil fertility and topography, and most species occurred at almost ali transects sampled. The number of individuais per transect was negatively associated with soil fertility and topography. Araceae was the most important family of epiphytes, and represented over 60% of ali morphospecies. In density terms, Polytaenium guayanense and Heteropsis flexuosa were the most important epiphytic species. Polytaenium guayanense and Hecistopterispumila were significantly more frequent on trees with DBH <10 cm and Philodendron sp.2 on trees with DBH> 10 cm. Overall, the herb community is similar in composition and structure to other arcas where there have been similar studies in Amazon and its spatial distribution is uniform and little varied along gradients of the site analyzed. There is need for further investigations to understand patterns of variation of plant communities along environmental gradients since it is criticai to planning the conservation oftropical forests