Heteropterys pteropetala is a 1-2 meter height shrub characteristic from Cerrado vegetation, Brazil. Their anemochorous seeds are dispersed during the dry season (mid-May to mid-Sept). We investigated the effects of the fire season on sexual reproduction and population structure of this species in a cerrado sensu stricto at Reserva Ecológica do IBGE, Brasília, DF, Brazil. The study area is part of the Fire Program (RECOR/UnB), in which plots have been submitted to biennial fires in three different months (June, August, September) since 1992. A fourth plot (control) is protected from fire. We quantified the number of seeds dispersed each month, tested the effects of high temperatures on seed viability and germination, estimated the population dispersion and density, and measured the individual's height and basal diameter in each plot. Seed dispersal occurred from Jun to Sept, but 90% of the seeds was released between July and Aug. Temperature treatments of 60 ºC/40', 80 ºC/10' and 100ºC/2'30" had no effect on seed viability (>80%) and germination (>70%), but exposures to 100 ºC/5', 100 ºC/10' and 200 ºC/1' killed about 50, 90 and 100% of the seeds, respectively (n=200 seeds/treatment). Population dispersion was aggregated in the four plots (Morisita Index>1). Individual's average height and basal diameter were similar among plots. Population density was low in the early-fire plot (burn in June), but in the mid- and late-fire plots (Aug and Sept) it was similar to control plot. We suggest that early-fires kill most seeds, because they are still attached to mother-plants, indeed subjected to extreme temperatures (~500 ºC). In Aug (mid-) and Sept (late-fire) seeds have been released and may be buried and protected from extreme temperatures during the burning. The results suggest that early-fires reduce plant recruitment mainly by its effects on seed survival and germination.
Heteropterys pteropetala; Cerrado; fire; population structure; germination; savannah
