THE EFFECT OF WATER-SUPPLY ON TREE SEED-GERMINATION AND SEEDLING SURVIVAL IN A TROPICAL SEASONAL FOREST IN VERACRUZ, MEXICO

In tropical seasonal forests, mass seedling death may incidentally occur early in the rainy season following untimely germination provoked by an isolated heavy rainfall. We hypothesized that, in a soil with little moisture retention capacity, irregular rainfall patterns would result in large fluctuations of water supply and, in the early wet season, drought episodes could cause seedling death. This hypothesis was tested in a seasonal tropical forest in Mexico where seedling density is low and the soil consists of almost pure sand with a low water retention capacity. Various patterns of simulated rainfall were applied in the forest to seeds and seedlings of three common tree species. Overall very little difference in germination and seedling survival was observed between the various rainfall treatments. The results showed that rainfall patterns and the soil texture may interact in a much more complex way than was initially hypothesized, and that water availability to seeds and seedlings is not necessarily predictable. The absence of seedlings of the three tree species might be better explained by high seed predation and low light level in the understorey.