Seed-bank dynamics of the tropical weed Sida rhombifolia (Malvaceae): incidence of seedling emergence, predators and pathogens

Arrowleaf sida (Sida rhombifolia) is a tropical weed that grows in disturbed areas. Its control by hand pulling and mowing are only partially effective because arrowleaf sida is difficult to pull and quickly sprouts after cutting. We studied the seed-bank dynamics of S. rhombifolia in the region of Campinas, Sa˜o Paulo State, Brazil for 2 years, following a known number of seeds placed artificially at five burial depths. Predators and pathogens were responsible for the loss of c. 40% of the seeds during the first year of the experiment. The importance of predation declined with depth. Mortality due to fungal attack did not differ among the burial depths, except for seeds placed at the surface (where it was negligible). Seedling emergence only occurred during the first year, after the beginning of the rainy period and when the study area was still free of a dense vegetation cover. Seedlings did not emerge from depths greater than 5 cm.We conclude that seedling emergence and death are significant causes of seed losses fromthe seed bank of S. rhombifolia but their relative importance is highly dependent on depth of burial.