Pre-germination temperature and the survivorship and onward growth of Mediterranean fire-following plant species

The role of heat shock in the induction of seed germination for numerous Mediterranean fire-following plant species is well documented. However, the influence of pre-germination heating of seeds upon seedling survivorship and onward growth has not been studied. The aim of the experiments described here was to investigate how a range of heat treatments affects seedling survivorship and onward growth for six common fire-following Mediterranean plant species (Anthyllis vulneraria, Cistus creticus, C. salvifolius, Hippocrepis unisiliquosa, Pinus brutia and P. halepensis). In the first experiment, seeds of five species were heated to temperatures ranging between 80 degrees C and 120 degrees C (at 10 degrees C intervals) for 10 min and subsequent seedling growth monitored over 8 weeks. Survivorship for two pine species (Pinus halepensis and Pinus brutia) was reduced after seeds were heated above 90 degrees C. Onward growth for Pinus halepensis and the legume, Anthyllis vulneraria, was negatively affected by increasing pre-germination temperature. Survivorship and growth for both Cistus species was unaffected by heating seeds up to 110 degrees C. The second experiment examined more closely seedling performance of Hippocrepis unisiliquosa seedlings when seeds were heated to temperatures ranging between 50 degrees C and 90 degrees C (at 10 degrees C intervals) for 5, 10, 15 and 20 mins. Increasing pre-germination temperature and the length of time seeds were exposed to heating significantly reduced seedling growth rates in this species. The effect of fire on seedling emergence, growth and survivorship in the field is discussed with reference to the adaptation of the six species to post-fire regeneration and the patterns of seedling regeneration observed in the field. (C) Elsevier, Paris.