Estrutura e composição florística de comunidades de plantas em relação à distância geográfica na Amazônia Oriental.

Abstract

Understand the patters that explain the high species richness, diversity and plant distribution are still questions very complexes and little studied in the tropical regions. Two main models are applied to explain these patters in tropical regions: The Neutral and Niches models, in the former related that the species distribution results of the biotic parameters, while the second model report that species distribution are results of no random processes. Some studies have reported that species richness, diversity and floristic composition decreased with geographic distance in tropical regions. The object of this dissertation is test difference in the species richness, diversity, plant distribution and forest structure in a tropical forest in the oriental Amazonian in relation to geographic distance. This study was carried out in the six forest plateaus situated in the Saracá-Taquera National Forest in the Pará. The data analyzed in the study were obtained in a forestry inventory done in throughout the plateau using plots of 10 x 250 m. In the study were selected some plots situated in the center and edges of the plateaus. The number of plots analyzed at each plateau it varied from 18 to 22. The distance between the plateaus varied from 5.1 to 23.7 km. The number of plots used in each plateau varied from 18 to 22. The total species richness varied from 277 to 401 species and the number of rare species varied from 63 to 113 species. The total diversity index varied from 4.2 to 5.0 among the plateaus. The ten species with larger density and frequency varied among the six plateaus, with only two species common to the six plateaus with relationship the those parameters. The majority of species have low absolute frequency in the plots sampled and it lowers abundance, a normal pattern reported to tropical forests. The number of cumulative species in relation to sampled plots didn't have tendency of asymptote in the plateaus which is also an expected patterns to tropical forests and shows in the richness estimators used in the study. The distribution of tree in relation to diameter exhibited a log-normal curve, with high proportion of individuais in the first diameter classes. There is significantly variation in the species richness, diversity, density and number of rare species among the plateaus. There is a negative correlation between floristic composition and geographic distance within and between the plateaus. The results of this dissertation clearly shows that species richness, diversity and floristic composition varied among the plateaus, being the last parameters negative correlated with geographic distance corroborating the presented results done by others studies. Due to lower species richness obtained between the plateaus analyzed should recommended that part of the area of each plateaus be preserved.