Influence of heat shock on seed germination of plants from regularly burnt savanna woodlands and grasslands in Ethiopia

The effect of heat shock on the germination of seeds of 21 plant speciesfrom fire-prone wooded savanna ecosystems in western Ethiopia was analysed inorder to examine the possible implications of fire upon plant regenerationafterthis disturbance. Seeds were subjected to 6 different heat intensities (20, 60,90, 120, 150 and 200°C) for 1 or 5 minutes, in ordertosimulate the situation in the upper soil layers or on the soil surface duringfires. Germination tests were carried out in pots in a greenhouse over 20weeks.After 9 weeks no more seedlings emerged. There was wide interspecific variationin the responses of seeds to the different treatments. In all species,germination was significantly affected by the temperature treatment level.Shortexposure of seeds to high temperatures generally stimulated germination whereasprolonged exposure reduced seed germination. However, some species eventolerated 5 min treatment at 200°C. Seedheat resistance was positively correlated with seed length and mass among thespecies. Hence, production of large seeds with protective tissues promotessurvival in fire-prone savanna areas. Also, the seeds of some species showedboth a low and a high temperature optimum which ensures that at least someseedsgerminate in the absence of fire, but also that viable seeds still remain ifsubsequent late fires kill emerging seedlings. Frequent and light burning inwooded savanna grasslands seems to stimulate and enhance germination of most ofthe studied plant species.