Early Plant Succession after Cutting and Burning in the Upper Rio Negro Region of the Amazon Basin

Abstract

(1) Changes in vegetation structure, species composition, and species dominance were studied over the first twenty-two months of succession after the cutting and burning of several mature tierra firme (i.e. non-flooded) forest sites in south Venezuela in the upper Rio Negro region of the Amazon Basin. To explain the observed succession, additional field investigations were undertaken. (2) Four months after burning the density of plants was less than 1 m-2. The density of successional woody plants, forbs, and grasses increased rapidly from the fourth to the tenth month of succession. There was little change in plant density between the tenth and twenty-second month, but a large change in vegetation height occurred during this time. By the twenty-second month a loose canopy of Cecropia spp. was present at 5 m height. (3) Many of the forest tree species sprouted from the stump when cut, but burning killed sprouts and significantly reduced the size of the seed bank. Nevertheless, the first successional woody colonizers established from seed which survived the burn. The first forb and grass colonizers established from seeds dispersed onto the site after the burn. (4) The common successional woody species had bator bird-dispersed seeds. Many forbs and grasses had wind-dispersed seeds. (5) Population densities were low during the first months of succession because of the low density of propagules and because the low rainfall during this time was not favourable for seedling germination or establishment. The rapid increase in plant density after about the fourth month occurred because the early colonizers had then begun to produce, and disperse locally, large numbers of seeds. (6) There were six distinct microhabitat types present on the sites after burning. Most species tested showed distinct microhabitat preferences.