Regeneração natural de espécies lenhosas e suas correlações com fatores ambientais na mata de galeria do córrego Pitoco

Abstract

Studies carried out in natural enviroments, particularly in gallery forests, have been demonstrating the correlations between environmental factors and spatial distribution of wood species. However, it is not yet clear in which development stage these factors start to be preponderant in the spatial distribution of the species. This work aims to evaluate the existence of correlations between the floristic communities previously classified in the Gallery Forest of the Pitoco stream, located in the Ecological Reserve of the IBGE, Brasilia, DF, with local environmental factors. The regeneration was evalueted from 100 samples (10 m × 10 m), shared in two sample blocks (a e b), each one with 50 samples, perpendicular to the slope terrain. The seedlings (height < 1 m ) was evalueted in sub-samples of 2 m × 2 m, located into 5 m × 5 m sub-samples, where the saplings (height > 1 m and diameter < 5 cm). From results of vegetation survey available to this area, were selected 10 most important species of seedlings and saplings resulting in 16 species analyzed. The number of individuals from this species of seedlings and saplings, previously classified as “shade tolerant” and “light demanding”categories were evaluated in function of the canopy opening intensity. A hundred soil samples (0-10 cm) were collected and analyzed in function of its physicist- chemistry composition features, in sub-parcels (5 m × 5 m) shared in two sample blocks (a and b). The “Quota” variable is also measured through precision altimeter, aiming to show the topographical profile. The soil variables Ca, Mg, Mn, pH, Al, N, P and Fine Sand (mainly components) were analyzed through the PCA analysis, jointly to the floristic classification information (TWINSPAN). A CCA analysis was also carried out to identify the correlations between soil physicist-chemistries variables, “Quota”, canopy intensity opening and nominal environmental variables “Cerrado edge” and “Soil type”, with the spatial distribution of the species and floristic communities. Although the canopy intensity opening wasn’t significantly correlated with the number of “shade tolerant” and “light demanding”individuals through Sperman correlation in 5% probability, there were major differences between species in function of the luminous requirement category for the saplings than seedlings. The PCA result from the analysis suggests that the “dry community” showed greater correlations for Ca, Mg, Mn, pH and the “humid community” for Al, N, P and Fine sand. The “Quota” variable did not show expressive correlation (< 0,3), being excluded from the analysis.The correlation between the floristic communities and natural regeneration was clearer for the saplings category. The CCA result, although the analysis had included more variables, it was similar to PCA, indicating that the fertility and humidity gradient which related to the topographical gradient, were the main responsible for the distinction between communities, in despise of the canopy intensity opening. This last analysis also showed that the saplings category presents stronger correlations with the environmental factors than seedlings, beyond of seeming to relate more to the pattern previously for the trees category (DAP ≥ 5cm).