Efeito do fogo anual na mortalidade e no banco de sementes de Andropogon gayanus Kunth. no Parque Nacional de Brasília/DF

Abstract

Andropogon gayanus was introduced in Brazilian territory for pasture formation and spread
over large areas of natural ecosystems, currently being considered a threat to the diversity of Protected
Areas. Andropogon gayanus is a good resprouter species and is considered fire resistant. This work aimed at
evaluating the effect of annual burning, at the end of the dry season, on plant mortality and on soil seed bank
of this invasive species. The fires were conducted in September 2009, 2010 and 2011 in an area of cerrado
ralo invaded by A. gayanus in Parque Nacional de Brasília. The survival of 50 individuals of the invasive
species was monitored bimonthly after each burn until the day before the following fire. The effect of fire on
soil seed bank was estimated by comparing the germinable seed bank before and immediately after each fire. The mortality of individuals ranged from 8% to 10%, being restricted to individuals with basal diameter
smaller than 16cm. The density of viable seeds bank in the soil was 325, 375 and 400 seeds/m2
before the
fires of 2009, 2010 and 2011, respectively, with a reduction of 71%, 82% and 79% after these fires. Although
the fires have reduced significantly the invasive species seed bank, the low mortality of individuals, including
for the small individuals indicates that the species is resistant to fire and that, with the rapid resprout, there
will be the replacement of the seed bank in the next reproductive season, without the interruption of the
invasion process