Seed bank dynamics and tree-fall gaps in a northwestern Mexican Quercus-Pinus forest

Questions: How does the seed bank respond to different types of tree-fall gaps and seasonal variations? How does the soil seed bank influence recovery of the standing vegetation in the mature forest and tree-fall gaps? Location: 1800 - 2020 m a.s.l., Quercus-Pinus forest, Baja California Sur, Mexico. Methods: Seed size, species composition and germination were estimated under different environmental conditions during dry and rainy seasons: a mature forest plot and gaps created by dead standing trees, snapped-off trees and uprooted trees. The soil seed bank was investigated using direct propagule emergence under laboratory conditions, from soil cores obtained during both seasons. Results: 21 species, 20 genera and 14 families constitute the seed bank of this forest community. Fabaceae, Asteraceae, Euphorbiaceae and Lamiaceae were the most frequently represented families in the seed bank. Floristic composition and species richness varied according to the different modes of tree death. Species composition of seed banks and standing vegetation had very low similarity coefficients and were statistically different. Seed bank sizes varied between 164 and 362 ind.m(-2) in the mature forest plot for the dry and rainy seasons, respectively, while soil seed bank sizes for gaps ranged between 23-208 ind.m(-2) for the dry season and between 81-282 ind.m(-2) for the rainy season. Conclusions: Seed bank sizes and germination response were always higher in the rainy season under all the environmental conditions analysed. Results suggest that timing responses to gap formation of the soil seed bank could be more delayed in this temperate forest than expected.