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Role of fire in the germination of chaparral herbs and suffrutescents

1987; Volume: 34; Issue: 3 Linguagem: Inglês

1943-6297

Jon E. Keeley, Sterling C. Keeley,

Plant Parasitism and Resistance

Fifty-seven herbaceous and suffrutescent species common after fire in chaparral were tested for their response to charred wood and heat shock of 120°C for five minutes. Over half of the species germinated readily without either treatment. These included all of the herbaceous perennial monocots, most herbaceous perennial dicots, and a number of annuals. In most species, the heat treatment reduced germination and only one species was stimulated significantly by heat. Forty-two percent of the species showed significant enhancement of germination with charred wood. For some perennials, such as Penstemon spectabilis and Romneya coulteri, and an annual, Papaver californicum, there was a near obligatory requirement for charred wood. Significant enhancement of germination in the presence of charred wood is now known for species in 10 plant families: Asteraceae, Boraginaceae, Brassicaceae, Caryophyllaceae, Hydrophyllaceae, Onagraceae, Papaveraceae, Polemoniaceae, Rubiaceae, and Scrophulariaceae. Several fire-following species, Eucrypta chrysanthemifolia and Dicentra spp., failed to germinate under any treatment. Since the early observations of Brandegee (1891), botanists have been impressed by the often spectacular wildflower displays that occur the first growing season after wildfire in chaparral. Over 200 species of annuals, herbaceous perennials, and short-lived suffrutescents have been recorded from chaparral burns. This abundance and diversity of herbs is in marked contrast to the generally depauperate herbaceous vegetation in mature chaparral (Sweeney 1956, Stocking 1966, Keeley et al. 1981). Nearly all of this temporary vegetation arises from seed or vegetative parts present in the soil prior to burning. This fact has resulted in two theories accounting for the breaking of seed dormancy after fire: 1) seeds are inhibited from germinating by the mature chaparral vegetation (allelopathy) and fire releases seeds from this inhibition, or 2) seed germination is stimulated by fire. The question of allelopathic inhibition of seeds by chaparral has been examined in numerous studies (Sweeney 1956, McPherson and Muller 1 969, Christensen and Muller 1 975a,b, Kaminsky 1981, Keeley et al. 1 985), but its role in inhibiting seed germination is unclear. Madrono, Vol. 34, No. 3, pp. 240-249, 1987 This content downloaded from 157.55.39.106 on Mon, 25 Apr 2016 07:02:32 UTC All use subject to http://about.jstor.org/terms 1 987] KEELEY AND KEELEY: FIRE AND GERMINATION 24 1 There is strong evidence, however, that many chaparral species have seeds that, under natural conditions, require a stimulus from fire for germination. Germination of some species is stimulated by heat shock from fire that ruptures the seed coat (Sweeney 1956, Christensen and Muller 1975a,b, Keeley et al. 1985). Germination of other fire-following herbs is stimulated by a chemical leached from charred (but not ashed) wood (Wicklow 1977, Jones and Schlesinger 1980, Keeley et al. 1985). Many species have been tested for their germination response to heat shock; however, the vast majority of chaparral herbs and suffrutescents have not been tested for their response to charred wood. Although germination of many chaparral species is apparently dependent upon one or the other of these fire-related cues, a number of species are known to germinate readily without such cues (e.g., Sweeney 1956, Keeley et al. 1985). The purpose of this study was to test the germination response of 57 species, representing all of the life-histories and growth forms present in the temporary postfire vegetation. Specific questions addressed were: 1) How widespread is charred wood stimulated germination? 2) For species with charred wood stimulated germination, will heat shock produce a similar stimulation in germination? 3) To what extent can generalizations be drawn concerning the relationship of growth form and germination response?