Efeitos do fogo recorrente no banco de sementes: implicações para a regeneração de florestas degradadas na Amazônia

Abstract

Forest fires are increasingly intense in the Amazon and the accentuated degradation of the forest is a consequence of repeated burnings, which generally occur in anomalous periods of drought. Soil seed banks can act as an important source in forest regeneration, and information on floristic composition is vital to determine the resilience of plant communities. The objective of this study was to analyze the effects of recurrent fires on the soil seed bank of terra firme forests in the Amazon. The study was carried out in the Tapajós-Arapiuns Extractive Reserve, Santarém-PA, Brazil, in three types of forests: unburned forests (preserved reference forests), burned once (2015) and twice (2015 and 2017). All woody plants (over 2 cm DBH) and natural regeneration (under 1 m height) were monitored using permanent plots of 0.25 ha. The seed bank was collected in each habitat, using quadrants measuring 20 x 20 cm and 5 cm deep, and soil samples (N=2.8 m²) were placed to germinate in a greenhouse for seedling emergence for six months . Species were identified and classified according to life form, ecological succession and dispersal syndrome. 25 families, 33 genera and 39 species (12 trees, 11 shrubs, 13 herbs and 3 lianas) were identified in the seed bank of all sampled areas. Recurrent fire did not significantly affect seed bank density, with unburned forests presenting a density of 918 ± 329 seeds/m2 and forests burned once and twice reaching 681 ± 260 and 925 ± 315 seeds/m2, respectively. Floristic and functional composition, on the other hand, differed between habitats. In the seed bank of forests burned twice, there was a higher proportion of herbaceous plants (10.08%), including grass species, such as the Axonopus compressus species, which hinder forest regeneration. The seed bank is dissimilar to the aboveground plant community in all forest types analyzed. Therefore, the need for intervention is suggested, as the species found have little impact on the functionality of these ecosystems, causing a slow regeneration process.