Ecophysiology of fire‐stimulated seed germination in Cistus incanus ssp. creticus (L.) Hey wood and C. salvifolius L.

Abstract

Abstract. Seed germination characteristics were investigated in the most common Cistus species in Greece, namely C. incanus ssp. creticus and C. salvifolius. In addition to the soft seed subpopulation, both species produce a large fraction of hardcoated, water‐impermeable seeds which can be softened and, thus, promoted to germinate by mechanical scarification and thermal pretreatment. Temperature and light control of seed germination are unimportant. In the ecological context of the Mediterranean ecosystems, the eventually advantageous, opportunistic strategy of germination is based on: (a) seed heterospermy (which allows the smaller, softcoated fraction to germinate promptly each year while the majority of the seeds, the hard ones, accumulate in the soil); (b) the seed population heterogeneity in relation to coat hardness (so that any heat conditions produced by fire induce the softening and germination of a certain seed fraction); (c) the notably low germination rate (which suppresses premature germination); (d) the wide, Mediterranean‐type (relatively cool), temperature range of germination (while higher temperatures simply inhibit but do not induce any dormancy); and (c) the apparent lack of photo‐sensitivity (enabling germination under every light regime). In non‐fire years, the temporal distribution of field germination and seedling appearance might be partly determined by the seed dispersal strategy of the individual Cistus species. Nevertheless, the post‐fire regeneration response is manifested in the form of a huge wave of germination (of practically all seeds softened by the fire heat), shortly after the onset of the rainy season.

Seedling growth of four fire‐following Mediterranean plant species deprived of single mineral nutrients

“…The seeds of C. creticus have been shown to rely on fire in order to break seed dormancy imposed by hard seededness (see references in Thanos & Georghiou 1988). The results obtained in this experiment suggest that post-fire increases in nitrogen and potassium availability are also essential if newly germinating C. creticus seedlings are to establish successfully in the post-fire community.…”

Germination capacity and temperature dependence in Mediterranean species of the Balearic Islands

“…bianorii (Ayerbe and Ceresuela, 1982;Salvador and Lloret, 1995). This could be due to the presence of dormancy mechanisms in a large percentage of the seeds, as already described in Cistus species (Thanos and Georghiou, 1988;Delgado et al, 2001). Seed dormancy has been argued as a mechanism by which plants have adapted to unpredictable or seasonal environments (Bender et al 2003), as the Mediterranean climate.…”

“…Cistus albidus presents dormancy due to the hardness and impermeability of its coat, which were broken with dry-heat pre-treatment placing seeds, spread on glass dishes, in an oven already at 90°C for 5 minutes (Thanos and Georghiou, 1988;Hanley and Fenner, 1998). In the case of P. lentiscus, fruit pulp was removed (García-Fayos and Verdú, 1998).…”

Aspects of Demography in Post-Fire Mediterranean Plant Communities of Greece

“…Seed germination is not only enhanced by fire in many species but it results in significantly higher densities sometimes reaching 300 seedlings m-2, as in the case of Cistus species. Seed germination for the phryganic species tested so far reveals a mechanical rupture of the hard seedcoat for members of the Cistaceae (Arianoutsou and Margaris 1981b; Vuillemin and Bullard 1981;Thanos and Georghiou 1988;Trabaud and Oustric 1989;Roy and Sonie 1992) and for members of the Leguminosae (Doussi and Thanos 1993). Light quality has also been found as cueingseed germination for the phryganic species Sarcopoterium spinosum (Roy and Arianoutsou 1985).…”