INFLUENCE OF HEAT ON SEED-GERMINATION OF 7 MEDITERRANEAN LEGUMINOSAE SPECIES

The influence of high temperatures (dry heat and hot water) on germina tion of seven Mediterranean Leguminosae species typical of fire-prone ecosystems in southern Spain is analyzed, in order to know the respons e of seeds to wildfires and the possible implications in their regener ation after this disturbance. Seeds were heated to a range of temperat ures (50 degrees-150 degrees C) and exposure times (1-60 min) similar to those registered in the upper soil layers during wildfires. Germina tion tests were carried out in plastic Petri dishes over 60 days. In g eneral, the degree of seed germination promotion by dry heat treatment s showed a wide interspecific variation, although the final germinatio n level was increased in all the studied species except for Scorpiurus muricatus. The thermal pretreatment of 50 degrees C, however, was not effective for germination in any species, and rising the temperature to 70 degrees C only slightly enhanced the germination in Cytisus pate ns. The preheatings of 90 degrees C (5 and 10 min), 120 degrees C (5 a nd 10 min), and 150 degrees C (1 min) were the most effective in promo ting seed germination. Hot water (100 degrees C) scarification also in creased the final germination level in all cases, with the exception o f C. patens. The germination rates after preheating were much lower th an in mechanically scarified seeds and closely resembled those of the untreated seeds, except for C. reverchonii, whose seed germination rat e decreased with heat. The response of species to heat shock had no cl ear relationship with life trait or with the specific post-fire regene ration strategy (obligate seeder or facultative resprouter). Those spe cies coexisting in the same habitats had different heat optimal requir ements for seed germination, an strategy suggested by some authors as minimizing interspecific competition in the secondary succession start ed after fire.