Seed germination response to smoke of fynbos plants
I recently read an interesting article in the South African Journal of Botany which dealt with the germination response of fynbos plants to smoke. It may be of some help in trying to determine when to use smoke papers (although in nature there is always an exception to the rule). The findings could possibly be applied to the bushveld and grassveld areas of SA where fire plays an important ecological role.
The article is:
Brown, NAC, van Staden, J, Daws, MI and Johnson, T . 2003. Patterns in the seed germination response to smoke in plants from the Cape Floristic Region, South Africa. South African Journal of Botany. 69(4): 514-525.
You can contact Dr Brown at the NBI for a copy of the paper. A list of species and their responses to smoke is given in the article.
From their findings and that of authors mentioned in the text, the following can be noted:
The heat from fires stimulates germination of seeds of wild plants in fynbos and other Mediterranean vegetation types, particularly those with hard, impenetrable coats. Smoke from fires, independently of heat, can also stimulate germination. This is quite widepread in fynbos but is not found in all fynbos plants. Families in which species showed a significant response to smoke included the Asteraceae, Bruniaceae, Crassulaceae, Ericaceae, Geraniaceae, Mesembryanthemaceae, Proteaceae and Restionaceae (refer to the species list in the article as some members of these families show no response).
No species responded in the families of geophytes such as Amaryllidaceae and Hyacinthaceae and in the Iridaceae the majority of species studied (also geophytes) did not respond. It was found that the geophytic growth form was a robust indicator of response to smoke - geophytes exhibit a very low germination response to smoke. In many geophytes, flowering, rather than seed germination, is triggered by smoke.
Serotinous (late flowering) species have seeds that are less likely to respond to smoke than non-serotinous species, presumably as a consequence of their seeds not being in the soil when fire occurs. It also indicated that plants with some capacity to re-sprout are less likely to respond to smoke than obligate seeders. (Re-sprouters are plants that are able to resprout after being damaged by fire while obligate seeders are plants that are killed by fire and rely on seed for their recruitment). Many re-sprouters and serotinous species are woody and so it can be generalised that woody fynbos plants do not show a germination response to smoke. Non-serotinous annual and herbaceous species with no ability to re-sprout post fire, do show a positive response to smoke . In serotinous species and re-sprouters seed dispersal and not seed germination is triggered by fire.
It is generally accpeted that there is a relationship between seed size and germination response to light. Because small seeds lack the initial seed reserves for the seedlings to persist in low light conditions, small-seeded species are more likely to respond to light, as a germination cue, than larger seeded species. In this way they then avoid germinating in the shade. For fynbos plants it was found that seed mass is not a reliable predictor of response to smoke. This suggests that, in contrast to the effect of light, small seeded fynbos plants are not any more or less likely to respond to smoke than large seeds. Further investigation into the response of fynbos seeds to light and smoke is required.
The paper concludes:
"Clearly, further work is required to understand the ways that smoke induced germination contributes to regeneration success in the field and to more fully understand the regeneration niche requirements of fynbos plants."