SA Orchids:Fire

Veld fires are common in the summer and autumn months in the southern African region, and many plants are adapted to such fires. While shrubs like proteas are able to resprout or reseed soon afterwards, this phenomenon is even more pronounced in geophytes like terrestrial orchids and bulbous plants (most prominently in the 'fire lilies', Cyrtanthus species; family Amaryllidaceae).

In some southern African orchids it has been known for centuries that fire will profoundly stimulate flowering in the following season. A sudden mass flowering can then often be seen. In the years between the burning, only leaves or nothing at all can be seen above the surface in some species, and it may take many years until another fire brings a stimulus for renewed flowering. Interestingly, all orchids which are strongly stimulated by fire are found in the Western Cape. The phenomenon that fire has a dramatic effect on the flowering of terrestrial orchids is also found in other parts of the world which have a similar Mediterranean climate, e.g. western Australia.

In many southern African orchids fire merely enhances their flowering, but there are also others where flowering individuals can only be found following a fire; in some cases only in the first year after the burn. These species are very sporadic, only flowering in response to fire and thereby creating the impression that they are extremely rare. However, there are also orchids which can only be seen flowering in mature (= unburnt) vegetation, which do not require the stimulus brought by the fire.

While it is widely know that flowering of most southern African terrestrial orchids is clearly enhanced by fire, the mechanisms and physiological causes of this phenomenon are still not satisfactorily understood. To a certain extent the sudden heat, the chemical effect of the ash and the removal of the undergrowth by the fire may play a role, but there is also evidence that it is the ethylene gas released by the fire which induces the flowering.

Illustrations on this page:
(Top)Pterygodium acutifolium in a burnt marsh in Silvermine (Cape Peninsula)
(Lower) Satyrium coriifolium on Red Hill (Cape Peninsula)

Description and images : Hubert Kurzweil
October 2000