Abstract
Background: The Amazon basin contains mainly unflooded forests, and they are among the most important ecosystems in the world. Field experiments on seed processes are very important in order to understand the structure, function and dynamics of these forests. Methods: And so tree seeds of three species (Cecropia latiloba, Guarea macrophylla, Socratea exorrhiza) were set out in Amazon unlogged terra firme forest, in Amazon selectively-logged terra firme forest, in Amazon palm forest, and in Amazon white sand forest either on top of or beneath the litter layer, and after two weeks scored for seeds taken by predators, seeds destroyed by pathogens and seeds that germinated. Results: I found both terra firme forests (unlogged and selectively-logged) lost most of their seed to predators and the least of their seed to pathogens, white sand forests lost the least of their seed to predators and the most of their seed to pathogens, and the fewest seeds germinated in both terra firme forests and in palm forest. More specifically (1) within unlogged terra firme forest addition of litter reduced seed predation but increased seed losses to pathogens and germination, and C. latiloba lost the most seeds to pathogens, (2) within selectively-logged terra firme forest seeds showed the same trends as unlogged terra firme forest but without significant effects, (3) within palm forest addition of litter reduced predation but increased losses to pathogens, and S. exorrhiza lost the least seeds to pathogens, and (4) within white sand forests addition of litter increased germination. Combining the results from all forests together, predators took most of the seeds, pathogens took most of the seeds that escaped predation, and most of the seeds that survived predation and pathogens germinated. Conclusion: While such large losses of tree seed to predators and pathogens in these unflooded forests suggest limited recruitment, the variation demonstrated in these field experiments – among forest-types, among tree species, between litter situations on the forest floor – help to insure that recruitment does occur and that these unflooded forests continue to dominate the Amazon basin.
Highlights
The Amazon basin contains some of the most important ecosystems in the world, significantly influencing the water, oxygen, carbon and other biogeochemical cycles for the entire planet
Forest-types differed significantly for seed losses to predation (Table 1: df = 3, F = 5.4, p = 0.03) and white sand forests were lower than the other forest-types (46.1±2.3% [mean±standard error] of seeds taken, 90.2±3.5% for unlogged terra firme, 73.3±1.9% for selectively logged terra firme, 81.8±4.4% for palm)
In unlogged terra firme forests seed predation was significantly different between litter treatments (96.1±7.2% no litter vs. 84.4±3.8% litter), seed pathogenic attack was significantly different among tree species where Cecropia latiloba (19.2±1.2%) was higher than Guarea macrophylla (4.4±0.9%) or Socratea exorrhiza (1.5±0.3%) and significantly different between litter treatments (4.1±1.1% no litter vs. 13.4±2.1% litter), and seed germination was significantly different between litter treatments (0.6±0.1% no litter vs. 3.7±1.1% litter)
Summary
The Amazon basin contains some of the most important ecosystems in the world, significantly influencing the water, oxygen, carbon and other biogeochemical cycles for the entire planet. Research in the Amazon has shown seed predation determines the fate of the majority of seeds (Bodmer 1991, Notman et al 1996, Russo 2005, Paine & Beck 2007) but even after suffering such large losses of seed, tree seedlings, tree saplings and mature trees do occur and regenerate these Amazon forests. This must be due to critical sources of variation (SOV) in how these mechanisms (seed predation, seed pathogens) and environmental tolerances (seed germination) work. Field experiments on seed processes are very important in order to understand the structure, function and dynamics of these forests
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