Abstract
Human-induced wildfires are increasing in frequency in tropical forests, and their deleterious consequences for biodiversity include decreases in seed rain, which may be affected directly by fire or indirectly by the creation of edges between forest and non-forest environments. Understanding seed rain is key to assess the potential for natural regeneration in plant communities. We assessed the impact of fire and fire-created edges on seed rain species richness, abundance, size, weight, and dispersal syndromes in Atlantic Forest remnants in Bahia, Brazil. We assessed seed rain at monthly intervals for an entire year along seven 300 m-long transects placed perpendicular to the edge. We installed seed traps at the edge and at 20, 40, 60, 80, 100, and 150 m into the burnt area and into the forest from forest edge. We recorded a total of 9050 seeds belonging to 250 morphospecies. We did not observe edge influence; however, we detected a lower abundance and proportion of animal-dispersed seeds in the burnt than in the unburnt areas. The seed abundance in the burnt areas was lower and seeds were smaller and lighter than those in the unburnt area. Seed rain in the burnt area was not greater near to the forest than far from it. The abundance and richness of seed rain was positively correlated with tree density. Our findings highlight the lack of seed rain in burnt areas and differences in community composition between the burnt and unburnt areas. Collectively, these results indicate negative consequences on natural regeneration, which can lead to permanent secondarization of the vegetation and challenges for early regeneration of burnt areas, which will initially have impoverished forests due to low seed richness.
Highlights
Fires play a significant role in tropical ecosystems by influencing community structure and species composition (Bond and Keeley 2005)
The area is affected by anthropogenic impacts, especially those caused by deforestation for new agriculture fields, poaching, and extraction of wood and other plant products by local dwellers (GSCM, pers. obs.)
Seed abundance was highest in the forest, followed by the burnt area and the edge
Summary
Fires play a significant role in tropical ecosystems by influencing community structure and species composition (Bond and Keeley 2005). In tropical forests, the geographic extent of forests may be limited by fires as well as edaphic and climatic factors (Hoffmann and Moreira 2002; Russell-Smith et al 2004). Even though evolutionary history resulted in fire-resistant traits for some vegetation types (Hoffmann et al 2003; Pausas et al.2006; Maurin et al 2014), anthropogenic wildfires are an increasing threat to biodiversity. In tropical forests, wildfires used to be rare or absent (Thonicke et al 2001; Chisholm et al 2016; Barlow et al 2020) but have become a recurring disturbance (Armenteras et al 2013; Granzow de la Cerda et al 2012) in the last decades. Interactions with other anthropogenic disturbances, such as climate change and deforestation, are changing fire intensity and impacts (Kelly et al 2020, Driscoll et al 2021). In tropical rain forests, a single fire can release between 7.7 and
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