Role of Allelopathy, Heat and Charred Wood in the Germination of Chaparral Herbs and Suffrutescents

Abstract

Herbaceous and suffrutescent species are uncommon in mature chaparral but dominate after fire. Colonization is largely from dormant seeds in the soil. The role of allelopathic inhibitors and fire-related cues in the control of germination of species in the major life-history groups was examined. Herbaceous perennials are often dormant under the chaparral canopy and their presence in burnt areas is due to sprouts from bulbs or rhizomes. Their seeds germinated readily without any treatment and they were not inhibited by leachate from living Adenostoma fasciculatum foliage, but high temperatures were lethal to seeds of many species. Suffrutescents are not present under the chaparral canopy and their presence in burnt areas is due entirely to seed. Their germination was stimulated by heat, or powdered charred wood, or both, although a portion of the seeds of some species germinated without treatment. Opportunistic annuals have polymorphic seeds; a portion germinated readily whereas others germinated only after heat or charred wood treatment. The non-refractory seeds account for colonization into gaps in the canopy and the refractory portion accounts for their abundance immediately after a fire. Whether the non-refractory seeds are inhibited by allelopathic leachate from the Adenostoma fasciculatum canopy is equivocal; leachate did inhibit the germination of 2 [Apiastrum angustifolium and cryptantha muricata] of the 22 annual species investigated, but the germination of 1/3 of the species was stimulated by leachate. Fire-annual species are largely restricted to recently burnt chaparral sites and the seeds to these species remain dormant in the soil between fires. There is little germination without cues relating to fire. Some species responded to heat but the highest germination was with the charred wood or heat plus charred wood treatments.