O papel da serrapilheira na emergência de plântulas herbáceas de terra firme, Amazônia central, Brasil

Abstract

The relationships between topographic variables and distribution of herbs are widely recognized, but few hypotheses have been raised to explain the results. One of the hypotheses regarding the distribution of ferns in Central Amazonia is that the litter would be a mediator that would explain the greater species richness and higher density of such species in slope areas. We conducted a study in the Ducke Reserve, Manaus, Brazil, to test this hypothesis for all of understory herbs, manipulating experimentally the amount of litter in the field. We used 30 plots, covering an area of 25 km2 of tropical rainforest, with 5 blocks per plot manipulation. Each block was composed of sub-plots of the litter addition, control and litter exclusion. We measured the depth (in April and September/2010) and dry mass (May/2010) of litter, in addition to quantifying the reproductive individuals in the plots. We conducted observation of emergence grass for 10 months (December/2009 to September 2010). The measure of depth of litter in the wet season was negatively related to slope, but did not differ in relation to clay content in soil. The measures of dry mass, in the rainy season, and depth of litter in the dry season were not correlated with the slope of the land or with clay content. We note that seedling emergence was higher in the litter exclusion treatments, both in absolute emergency and seedling emergence in seedlings originating from small, not significantly different from control treatments and the addition of leaf litter in relation to emergence of seedlings arising medium and large. The clay was related to the emergence of all groups of propagules and seedlings of absolute emergency, but the head of reply in relation to clay content varied between the groups of seedlings. The presence of fruiting individuals in the plot was the best predictor for the emergence of plantlets from both medium and large seedlings. The results are consistent with the idea that very small seedlings are most affected by the physical barrier imposed by litter and herbs that apparently dispersed by ants have spread geographically limited. Furthermore, a system of directional movement of air associated with lower accumulation of leaf litter in slopes areas to are apparently those most responsible for the pattern of highest richness and density of ferns in these environments. Experimental studies in the field to address the dispersal of spores and linked the addition of seeds are needed to test the hypothesis grounded in this study.