Estabelecimento e desenvolvimento de Dalbergia miscolobium Benth. em duas fitofisionomias típicas dos cerrados do Brasil central

Abstract

The savannas of Central Brazil are characterized by a continuous, predominantly grassy, ground layer and an open layer of trees and shrubs of a variable density. In this study we examined the effects of drought, habitat type, the canopy light condition, herbivory and fire in the establishment and growth of Dalbergia miscolobium Benth., a legume tree typical of the savannas of Central Brazil. Saplings were transplanted into the grass matrix of a grassland with scattered trees and shrubs (“campo sujo”), and into the semi-closed canopy of shrubs and trees that characterized the “cerrado” physiognomy. Sapling survival, shoot growth, leafproduction and leafherbivory were followed monthly over a five-year period (1993-1998). Mortality occurred predominantly during wet periods, and seasonal drought was not an important mQrtality factor. Sapling survival was greater in the “campo sujo” and they even survived a fire at the end of the dry season of 1994, while severa I saplings at the cerrado site were killed. Shoot growth’was low, about 2.2cm/year in the “campo sujo”, and 3.1cm/year in the “cerrado”, mostly in the wet season. Leaves were shed during the dry season, and the peak in number of leaves in mid to late wet season was followed by a peak in leaf area loss by herbivory. Necrotic black spots, caused by the fungus Phoma sp. were observed in the leaves of most plants. Canopy shading could limit CO2 assimilation (Aco2) in the initial phases of plant development. Light measurements suggested that Scm tall saplings with horizontal leaves would receive enough Iight to reach, on an average only 32% of maximum Aco2 during the daylight period. Since the height of the grass layer was mostly less than 50cm, an increase in plant height from 5 to 50 cm would result in a twofold increase of Aco2 averaged over the daylight period. Thus, the development of D. miscolobium was restricted by water stress and herbivory during the dry season, and by shading and pathogen attack during the wet season.