Effect of high temperatures and ash on germination of ten species from gorse shrubland

Seeds of ten species of Cistaceae, Ericaceae and Poaceae were examinated to compare their responses to high temperatures and ash, simulating the direct effect of fire on germination. A variable response to these factors between families and within species from the same family was detected.In Cistaceae, heat treatment pre-sowing stimulated germination. In Ericaceae, germination was stimulated by thermic shock, but a wide range of response was detected (between all four species), from Erica ciliari, very sensitive, to Daboecia cantabrica and Calluna vulgaris which showed no significant response. The range of reaction shown by the species of this family suggest that the size of the seeds is directly related to the difference in response, at least in species with a similar structure. In Poaceae, germination was not found to be dependent upon thermic shock.The effect of ash varies in magnitude. Although it decreased the germination percentage in all species, in Avenula marginata (Poaceae) the effect was not statistically significant, whilst in Ericaceae, particularly in those showing the highest levels of germination in the control (C. vulgaris and E. umbellata), the effect is to inhibit germination completely. In respect to the effect of ash the families could be arranged in the order Ericaceae>Cistaceae>Poaceae.Complex interactions between various dormancy types and seed size could explain these results. In species which depend on physical dormancy temperature has an important role. When other dormancy type is dominant in the control of germination, the medium characteristics could have a relevant role on seed response. In addition, the seed-size could determine the threshold of tolerance to temperature.