Effects of soil flooding, sunlight and herbivory on seedlings of Annona glabra and Pachira aquatica in a tropical swamp

Wetland seedlings, in addition to dealing with the effects of flooding, must gain access to sunlight and avoid herbivore damage in order to establish. Understanding the effects of environmental factors on seedling growth and how plants modify their functional traits in response to them, is a challenge of wetland ecology. We evaluated the effects of different conditions of soil flooding (flooded and mesic), sunlight (closed and no canopy) and herbivory (presence and absence) on the survival, growth, and morphological traits of Annona glabra and Pachira aquatica seedlings, two dominant woody species of Neotropical swamps. We had eight experimental treatments with five replicates each. Our results showed that the survival of both species was high and was not affected by soil flooding, sunlight and herbivory. However, these factors affected plant growth rates. In general, the highest growth rates were observed in the treatment with high sunlight, mesic soil and herbivore exclusion. Both species displayed higher leaf biomass allocation under closed than under no canopy. Furthermore, under closed canopy conditions both species produced relatively more slender and taller stems, which may allow them to intercept light more efficiently. Also, both species showed low belowground biomass allocation in flooded soils, probably as a consequence of a high anoxic condition. Our results confirmed that soil flooding, sunlight and herbivory are important factors that influence the growth patterns of A. glabra and P. aquatica seedlings, but they do not affect seedling survival. This information may help resource managers to identify high-quality sites that deserve to be protected. Also, the knowledge on species responses to different environmental conditions may be useful in restoration programs for tropical swamp forests.