New views on the role of fire in the evolution of Mediterranean plants

A new review of the characteristics of plants in Mediterranean climate regions has found little evidence that fire has played an important part in the diversification of the flora, contrary to previously held views.

01 Mar 2011

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Nuytsia floribunda post-fire flowering

Post-fire flowering of Nuytsia floribunda after a summer fire in the Cape Arid National Park, Western Australia. Most wildfires occur in the dry summer-autumn, whereas prescribed burns are mainly carried out during the winter months for safety reasons. (Image: S.D. Hopper)

An opinion article by a team of researchers, including Kew’s Director Professor Stephen Hopper, has challenged traditional views of the role of fire in the evolution of the flora of Mediterranean climate regions. These habitats cover only 5% of the land surface of the Earth but are home to approximately 20% of flowering plant species and are found in Chile, California, South Africa, south-west Western Australia and the Mediterranean basin itself. They have been identified as biodiversity hotspots (due to their high diversity and species endemism, coupled with threats from habitat loss) and are therefore important areas for conservation, requiring careful management. Fire is a natural part of Mediterranean systems – and is particularly prevalent in Western Australia – but the increasing frequency of fires which affect humans has led to the introduction of regular prescribed burns as a means of preventing or ameliorating the effects of large wildfires.

Banksia speciosa cone and seedling

Banksia speciosa cone and seedling. Many banksias exhibit serotiny – the retention of seeds until an environmental trigger such as fire or death of branches causes the cone to open. (Image: S.D. Hopper)

Many ecologists and conservation practitioners advocate burning in these systems in a controlled way, believing frequent burns to be essential for maintenance of the habitat. However, this thinking is based on an untested assumption that the majority of Mediterranean plants are adapted to fire in the landscape. In addition to this, controlled burns are often carried out at inappropriate times of the year and with a greater frequency relative to natural wildfires, possibly threatening many plant species with decline and extinction.

The opinion article, published in the international journal Trends in Plant Science, reviews the characteristics of plants in Mediterranean climate regions and provides evidence to suggest that fire may not have been as important in the evolution of the flora as previously thought. Some characteristics that may appear to be adaptations to fire could have evolved previously for another function and others may have evolved in a fire-prone environment but in response to a different evolutionary pressure, such as drought.

The authors suggest how one could identify true fire-adaptations and provide evidence that throws doubt on the status of many plant characteristics that have been widely assumed to be prime examples of adaptation to living with fire. These include re-sprouting, serotiny (the retention of seeds until an environmental trigger such as fire causes release), seed and fruit dormancy, and smoke-induced germination. For example, re-sprouting after a fire is seen as a classic adaptation to fire in Mediterranean regions. However, it also occurs in response to many other environmental perturbations such as drought, frost, heat-wave, grazing, storm damage, excessive salt, etc. The characteristic is also prevalent in systems that are not prone to fire, such as deserts, rainforests and alpine heathland. The authors concluded that post-fire flowering is the only trait that has possibly evolved as a direct adaptation to fire.

The evidence

Fire-resistant traits:

  • occur in a variety of different climates and often pre-date the onset of widespread fire.
  • provide survival and reproductive advantages in other environments such as drought-prone, nutrient-limited or highly seasonal environments.
  • have arisen multiple times in the evolution of flowering and non-flowering plants, in fire-prone and non fire-prone environments.

The evidence suggests that although some characteristics of Mediterranean plants may prove advantageous in the event of a fire in the landscape, fire itself may not be the main evolutionary driving force.

Conservation implications

The ultimate question is whether these findings have implications for conservation policy and management in Mediterranean regions. If the clearly set-out and well-supported assertions of the authors are correct then the current regime of frequent burns in the management of Mediterranean landscapes may be placing many vulnerable plant species under threat. It is certainly time to re-assess the role of fire in the evolutionary history of these regions and to encourage further study to avoid unnecessary extinctions of plant species that may simply not be adapted to a life with frequent fire. The authors hope that their findings will encourage further scientific review and closer working relationships between fire managers and scientists, to achieve the best outcomes for human safety and biodiversity conservation.

Item from Dr Rhian J Smith
(Director's Postdoctoral Research Fellow, Royal Botanic Gardens, Kew)


Article references:

Bradshaw, S. D., Dixon, K. W., Hopper, S. D., Lambers, H., and Turner, S. R. (2011). Little evidence for fire-adapted plant traits in Mediterranean climate regions. Trends in Plant Science, 16: 69-76.  http://www.cell.com/trends/plant-science/abstract/S1360-1385(10)00233-5


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