Dinâmica do banco de sementes de áreas de cerrado com distintos históricos de incêndio em São Carlos, SP

Abstract

In heterogeneous communities both in time and space, the most important strategies and processes are successfully evaluated by long-term studies. For studies of the effects of disturbance in the seed bank function and formation, are necessary many samplings, sites and measures of biotic and abiotic variables. In this study, we aimed identify fire effects on the seed bank structure in different areas of cerrado sensu stricto in terms of structure and history of disturbance, in the campus of the Universidade Federal de Sao Carlos, São Carlos. One of these areas was burnt in 2006 , while the other burnt in 2009. Both in dry and wet season, we sampled the seed bank, since fire occurrence until the dry season of 2010. In 2007 and 2008 we collected soil samples only from first 4 cm depth, while in 2009 and 2010 we included the litter layer and from 5-8 cm depth. We estimated the number of viable seeds by the germination method, and used univariated and multivariated analysis of variance in PERMANOVA to perform the analysis of main effects of fire, year, season and depth, and all interactions. The seed bank was more abundant and diverse in the more preserved sites, and the most frequent species were Miconia albicans, Tibouchina stenocarpa e Panicum campestre. Otherwise, the seed bank of invaded sites was dominated by Melinis minutiflora and Urochloa decumbens. Fire effects decreased seed abundance in the soil. The abundance of U. decumbens e P. campestre increased soon after the fire in burnt sites, while M. albicans responses were slow but continuous. Although the seed banks of M. albicans e P. campestre were persistent through the soil profile, the soil seed bank of all sampled sites are small and poor to promote natural regeneration of the vegetation. As the impacts on this fragment, probably non-natural fires, are expected to continue, exotic grasses will expand toward more preserved. In this case, this fragment of cerrado sensu stricto 4 would be converted in grasslands dominated by the exotic M. minutiflora and U. decumbens.