Herbaceous lomas in the Peruvian coastal desert of South America establish in spring, and its habitat is limited to the southern or southwestern slopes along the coast that are affected by thick fog. The time of appearance, the duration and the thickness of the fog vary greatly from year to year, so the lomas can grow only in habitats with enough water to sustain seed germination and plant growth. This paper studies the species composition and density of the buried seed population of the herbaceous lomas of Loma Ancon in order to clarify the mechanisms of the lomas' establishment. The mean number of species with viable seeds was about 12 spp. m-2 and that of dead seeds was about 22 spp. m-2. The dominant species were Solanum tuberiferum, S. pinnatifidum and Nolana humifusa, both in viable and dead seeds. Viable seed density was about 5000-8000 seeds m -2, which is comparable with the seed densities of other herbaceous communities. Dead seed density was about 15 000-27 000 seeds m -2, or nearly three times the viable seed density, because the rate of decomposition was slow in the extremely dry conditions. The net increase of viable seeds by seed production was estimated at about 5000 seeds m -2 in 1980, and the increase in the number of dead seeds was 2200 seeds m -2.

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