Wildfires and soil: Where are we now?

Lorena M. Zavala. University of Seville, Sevilla, Spain
Antonio Jordán. University of Seville, Sevilla, Spain

Jorge Mataix-Solera. University Miguel Hernández, Elche, Spain
Artemi Cerdà. University of Valencia, Valencia, Spain

Are wildfires a natural ecological factor or an environmental problem?

According to official statistics, during the 1990’s, about 1.5 millions ha were burned in Spain. In the first decade of this century, the burned area in Spain also surpassed one million hectares. To put it in conventional TV surface units, the burned area in the past 20 years equals the provinces of Cáceres and Badajoz, or 274,000 soccer fields. The effects caused by the fire on the soil have been studied over the past 20 years by research groups who have made a significant contribution to the advancement and improvement of scientific knowledge.

Area affected by wildfires in Spain between 1991 and 2010.
Area affected by wildfires in Spain between 1991 and 2010. Source: Spanish Ministry of Agrictulture, Food and Environment.

Forest fires are a regular topic of conversation in our society, especially during summer conversations, and people agrees to describe forest fires as disasters. Instead, they disagree vehemently about forest management, restoration and prevention policies. We have never seen one of those familiar discussions in which a consensus has been reached. Nor have we seen people talking about the twinned management of fire and forest areas.

Picture by Pedro Ribeiro Simões. Click to see the original image and details.
Picture by Pedro Ribeiro Simões. Click to see the original image and details.

We can not understand fire as something alien to ecosystems. Undoubtedly, forest fires are an important part of the history of Mediterranean and most terrestrial ecosystems. Natural fires caused by lightning or other causes such as volcanic eruptions, have contributed to shape the history of vegetation, soils, and ultimately the landscape we know.

Fire has been used by humans since 400,000 years ago and only about 10,000 years ago man learned to light a fire without relying on natural agents such as lightning. Since then, the fire has been an excellent tool to harness and manage natural ecosystems worldwide. The Mediterranean landscape we know today has been shaped by the action of man for thousands of years, and the use of fire is not out of this process. The intense transformation of original forests in cropland and pastures since the fifteenth century to promote livestock, the exploitation of coal and wood, and human supply has been possible thanks to fire.

Since the mid-twentieth century, and as a result of urbanization and the abandonment of rural areas, traditional agricultural uses and management are being lost. Perhaps this is why, now, people see fire as an enemy that must be eradicated. The problem is not fire itself, but the modification of natural fire regimes in ecosystems. This has turned fire, a natural ecological factor, in an environmental problem. The solution therefore is not as simple as the total eradication of fire.

Burning shrubland. Picture by Antonio Jordán.
Burning shrubland. Picture by Antonio Jordán.

Protection of forest soils

Soil is a natural non-renewable resource in the short and medium term. It is the basis of forest ecosystems and its protection and conservation are essential. After a forest fire, soil properties may be affected with different severities depending on fire, vegetation and environmental characteristics. Together with the temporary decrease of vegetation cover, this makes soil very fragile and vulnerable to degradation processes. Too often, restoration of burned ecosystems in Mediterranean areas has forgotten soil. Both mismanagement, as not protecting soil at the right moment, may lead to the onset of irreversible degradation processes.

No forest recovery after the Hayman Fire (Colorado, USA). Picture by Artemi Cerdà. Click to see the original image and details at Imaggeo.

The scientific community, managers, users and owners must act together to promote the interchange of knowledge and experience. It is essential to develop protocols for action to identify critical and sensitive areas to take appropriate measures for soil protection and restoration of ecosystems affected by forest fires to minimize the damage caused by fire. Restoration plans should consider the option of natural generation, without special remedial measures in cases that require it. Just keep in mind that certain actions can cause more damage than the fire itself.

Research on restoration of fire-affected areas. Picture by Jorge Mataix-Solera.
Research on restoration of fire-affected areas. Picture by Jorge Mataix-Solera.

Are all fires equal?

In the current context of global warming and landscape degradation, research on the effects of fire and restoration of affected ecosystems is necessary. Forest fires can cause alterations on soil, water, and vegetation. Many plants need heat to germinate or sprout and grow. Others have developed different strategies to resist fire, like the canary pine (Pinus canariensis) or cork oaks (Quercus suber). In the case of soil, fire acts indirectly by destroying the vegetation cover, so that an increased risk of erosion occurs, but also directly through changes in soil physical and chemical properties. The magnitude of these changes depends much on fire intensity and severity or soil resilience to impacts.

Two very close fires in a oak forest in Cadiz (SW Spain), 17/06/2010. Both extinguished spontaneously in less than 2 hours.
Two very close fires in a oak forest in Cadiz (SW Spain), 17/06/2010.

Not all fires are equal. Throughout the year, hundreds of small fires that may occur spontaneously in a certain area. These fires are even beneficial to the mountain because they help to rejuvenate the forest cover and promote biodiversity. But there are also large forest fires. Large forest fires are less common, but affect very large areas (hundreds or thousands of hectares) and they simply can not be controlled until conditions change or all fuel is burned. So when we talk about fire fighting, we should also ask ourselves what type of fire do we want to prevent.

Depending on their properties, not all systems behave the same way after a fire. After high severity fires or after periods of high fire frequency, degradation of soil and vegetation may be very high. In other cases, the system may recover quickly and spontaneously. Ignorance of these processes and dynamics has often led to base the management of forest ecosystems at all costs suppression of fires. Good forest management should be based on scientific research. In many countries, fire policies have invested heavily in extinguish, few in preventing and scarce in the study of their impact on soil, water and vegetation. Knowledge and assessment of the impacts of fire on soil properties is essential when conducting management decisions, restoration of burned areas or prevention.

The scientific community, decision-makers, and society must be able to propose and use methods of assessing the impacts of fire on ecosystems. Despite the wealth of information existing in the literature, soil is often overlooked by restoration. For some reason, we are not able to look down and realize that soil is where roots and seeds live, and that a mere attempt to restore the original vegetation can be sentenced to failure if proper soil conditions are not met.

What can we do to prevent large forest fires? Some considerations

These are only some ideas. You can suggest new ones or discuss in the comments.

The actions to perform in the post-fire must be agreed between the entities and persons involved. These actions should be conducted only in areas where strictly required, considering the option of natural regeneration. We need to develop protocols for identifying potential vulnerable areas, regarding factors as the affected area, fire severity, soil type, slope and aspect.

Management of forest areas should be planned considering the risk of fire, limiting or controlling the access to hazardous areas, establishing discontinuities to reduce the risk of fire spread and the formation of large wildfires.

The wildland-urban interface should be reduced, especially in forest areas. Sparse buildings in forest areas (usually second homes for summer holidays) highly contribute to increase fire risk. Again, even in the case of low-severity fires, rescuing people from isolated areas increases the risk for those responsible for fire fighting.

Sound policies must be developed to encourage the sustainable use of forest resources: livestock, controlled extraction of wood, cork, pineapples, mushrooms, recreation and nature tourism. In forest areas where there are no other agricultural or industrial activities, these activities can generate economic activity with a relatively low impact on the ecosystem.

Authorities should plan budgets for implementing emergency measures to be applied immediately after the fire. Also, forest plans should, as a minimum, include emergency actions before the arrival of the first rainstorms after summer. Fortunately, emergency plans to protect soil from post-fire erosion in some regions are already the result of collaboration between scientists, managers and stake-holders. To achieve sustainable management of fire-affected ares, the exchange of experiences and knowledge between scientists and stake-holders must be continued.


This post has been published simultaneously in the EGU Blog Network.


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