Ecologia de Euxylophora Paraensis Huber em um fragmento florestal no município de Paragominas-Pará.

Abstract

Forest fragmentation in the Brazilian Amazon has increased alarmingly and is among the greatest threats to tropical biodiversity. Among the threatened tree species is Euxylophora paraensis Huber. It is an endemic species with natural occurrence restricted to the north of Brazil, in regions with a continuous and intense history of logging and conversion of forest cover to other uses. The aim of this work was to evaluate phenology and natural regeneration of E. paraensis in order to identify the influence of fragmented environments on the species reproduction. The study was carried out in a forest fragment adjacent to areas with bauxite mining activities, located in the municipality of Paragominas, southeast of Pará state, Brazil. For evaluating the phenology, activity and intensity of bud, flower and fruit data were collected from 38 seed bearers in the period from 2013 to 2017. Reproductive phenophases were related to the individual's distance to the fragment edge, dendrometrical measurements (DBH and height), climate elements and photoperiod, using multiple linear regression analysis. Natural regeneration was quantified and monitored using 10 circular plots with radius of 20 m each. The density of individuals of natural regeneration was evaluated at the edge and inside the fragment and also in relation to the matrix tree. The Periodic Annual Increment in diameter (PAIDBH) and height (PAIHT) were also determined and the GLM (General Linear Model) was applied to verify differences between environments and size of the individuals. The results indicated that the vegetative phenological pattern of the E. paraensis population is evergreen and the reproductive pattern is annual, regular, and long lasting. The reproductive phenodynamics (bud, flower and fruit) of the individuals observed was related only to climate elements. The matrix distance from the fragment's border and the size of the individuals (DBH and height) were not statistically correlated. The most significant climate elements for the reproduction of E. paraensis were rainfall, number of days without rain, average temperature, maximum of the maxima, minimum of the minima and photoperiod. Reproduction showed strong seasonality, occurring during the dry season. Regarding the natural regeneration, the density of individuals increased with the distance from the seed bearer with a negative correlation with the canopy area. The smaller is the canopy area, the greater the density of regenerating individuals. PAIDBH and PAIHT presented statistical difference in density, both in relation to the size of the individual and to the location in the fragment. There was a greater diametric increase in seedlings and trees in the edge area and a greater increase in height in the trees at the edge and inside the fragment. Thus, natural regeneration had effect of forest fragmentation, with higher germination and seed establishment at the fragment edges. No small trees were found in this environment. There are signs that the conservation of E. paraensis in risk, due to the increasing deforestation and fragmentation and the species fragilities to drastic climate changes. Such disturbances can impact flowering and fruiting and hamper the natural regeneration.