Heat-shock and seed germination of a group of Mediterranean plant species growing in a burned area: An approach based on plant functional types

Many plants from Mediterranean-type ecosystems show enhanced germination when exposed to heat and other fire-related cues. Whether Mediterranean-type plants are fire recruiters and need fire to germinate is subject of discussion. In the present work, we tested the above hypothesis by subjecting seeds from 57 species representative of a recently burned plant community to various heat pulses. Differences in germination among species, taking into account their phylogeny, were studied by dividing them according to their life-form (chamaephytes, hemicryptophytes), regeneration strategy (non-sprouters, sprouters) and geographical distribution range (Iberian Peninsula endemics, Mediterranean, widely distributed species). Seeds were exposed to 80, 100 and 120 °C during 10 min, and then, incubated at 17.5 °C for 6 weeks in darkness. Maximum germination was reached at 80 °C and control treatments and minimum germination was at 120 °C. Most species were tolerant to heat-shocks, only a few of them were stimulated by heat, and around 20% suffered a reduction in germination with heat. The germination response to heat-shock differed according to regenerative strategy and distribution range, but not to life-form. These results were supported independently of phylogeny. As expected, sprouters and Iberian endemics were more sensitive to heat-shock than non-sprouters and widely distributed species, respectively. As a conclusion, the studied plant group appears to exhibit resistance to heat but not dependence on it for germination. Therefore, recruitment could be high after low intensity fires, but might be significantly reduced for most species after more intense fires.