Seed bank dynamics are a critical consideration for management of arid and semi-arid shrublands. In the threatened “coastal succulent scrub” vegetation (at Punta Banda, Baja California), we studied the seed bank's composition and size, as well as its dynamics as shown by field emergence and as inferred from literature reports on germination. We also analyzed sampling effort for both seeds and seedlings. The seed bank was sampled just prior to the rainy season, with 130 soil units of 7-cm diameter ×1-cm depth distributed systematically over 1.66 ha. The field samples were mixed together then laboratory samples (17 of 14 cm3) were taken for manual extraction of seeds. We found 25 species, mostly of short-lived herbs. Some obvious species of the local flora were not encountered. Overall density was approximately 11,807 seeds m−2, but densities differed by more than 100-fold among species. Analysis of sampling effort suggested that only 8–12 laboratory samples were needed to approach estimated asymptotes of the density of seeds and the number of species. Seedling emergence was recorded during four months on 30 randomly distributed and caged plots of 361 cm2. We found 22 species, mostly short-lived herbs. Most species were uncommon and the density per plot of all species was highly skewed. Modes per plot were 3–4 species and 129–256 seedlings. Analysis of sampling effort suggested approximately 15 plots were needed to approach estimated asymptotes of the density of seedlings and the number of species. Published information on seed germination was found for 75 species which have been reported from coastal succulent scrub in the Punta Banda area. Apparently, fire-related cues were required for germination in only 13% of these, while most species may require only moist winters. However, long-term dynamics of the seed bank, and its geographic variation, remain to be studied.
Vol. 52 • No. 1
Vol. 52 • No. 1