Fire and Acacia seeds: a hypothesis of colonization success

SUMMARY (1) The effects of natural and simulated fire on insect-infested seed germination, seedling emergence and on the viability of seed pools in the soil of Acacia sieberiana were investigated in a savanna in Queen Elizabeth National Park, Uganda. (2) There was a strong potential for the population of A. sieberiana plants to increase from the viable seed pool of about 800 seeds m-2. Seedling emergence was 167 seedlings m-2 after one fire. Seeds collected from the soil surface of burned areas produced significantly higher total germination rates (650%,) than those from unburned areas (10%/,) when tested in the laboratory. As expected, seeds located at shallow depths were stimulated to germinate more readily by fire then seeds located deeper in the soil. (3) The germination was significantly reduced by the high bruchid larvae (Bruchidius spp.) infestation. Bruchid larvae are more sensitive to fire than the seed embryo and, thus, the heat treatment indirectly leads to higher germination. (4) Regression equations were developed for predicting the mortality of seed and bruchid larvae under different fire intensities. (5) A conceptual diagram of germination success of A. sieberiana was developed.