Effects of distinct types of disturbance on seed rain in the Atlantic forest of NE Brazil

Abstract

In disturbed sites, some groups of seeds might be excluded from the seed rain due to their dispersal modes or seed size, and some groups might be successful as a result of dis- turbance effects. In the present study, we examined the seed rain in natural treefall gaps and in an area of regenerating forest following an accidental burning, which occurred 4 years before this study. Both of these disturbed areas were compared with nearby forest understorey. The number of seeds, number of species, and proportion of wind-dispersed seeds were com- pared between these disturbed and undisturbed areas. The treefall gaps have received lower numbers of seeds and species than the nearby understorey, but the number of wind-dispersed seeds did not differ between these areas. The lowest seed number observed in treefall gaps can be attributed to a lower number of animal- dispersed seeds, suggesting that animals may be avoiding treefall gap areas. A higher number of seeds and a lower number of species were ob- served in the burned area when compared to the adjacent understorey. The high number of small-sized seeds and of wind-dispersed seeds in the burned area was almost surely a conse- quence of the local production of the pioneer plants established after the burning. In this study, substantial differences were observed in the characteristics of the seed rain at disturbed sites, when compared with undisturbed under- storey. However, these two distinct types of disturbance showed quite differing patterns, as treefall gaps received lower number of seeds while the burned area received a higher number of seeds, with a greater proportion of wind- dispersed seeds. The exception was for species richness, which was quite low at both these disturbed sites.