The number of fires causing significant damage and putting lives at risk is increasing. What can we do about this? Researcher Johan Sjöström explains why fires in southern Europe are becoming so serious and how common birch trees can help to reduce the risk in Sweden.
Burnt-down houses, a smouldering landscape, and black, toxic smoke. This is the image of a devastating forest fire. Doesn't it feel like we're seeing it more and more often?
'Relatively speaking, there aren't actually more fires, but they are more costly. If we look at the area burned and the number of fires, it is not greater now than 25 years ago. However, the number of fire disasters is increasing. These are fires that either kill people or have very serious consequences for the country's gross domestic product, says Johan Sjöström, a RISE researcher who specialises in forest fires and their fuels, ignition, behaviour, and societal impact.
The increase in the number of fires can largely be attributed to climate change. As the Earth's temperature rises, so does the risk of fire. Relative humidity decreases, sucking the moisture out of dead material on the ground.
What cannot be explained by climate change is the increased amount of fuel. This is due to several different factors. In France and Spain, where we have seen major fire disasters in recent years, the affected areas have historically been heavily cultivated landscapes where people have farmed or kept grazing animals,' says Johan Sjöström, continuing:
However, small-scale farms are no longer economically viable and are being abandoned. Either forests are planted in their place, often comprising highly flammable trees such as pine, or residential areas are built with shade trees planted very close to houses. Many small farms are also simply left as they are. Over time, the land becomes overgrown with highly flammable shrubs and grass.
Deciduous trees are an inexpensive way to reduce fire risk
In order to address this problem, climate change must be mitigated and land use must change. The number of natural fire barriers provided by open landscapes needs to increase.
Taking France and Spain as examples again, the number of preventive, controlled fires in strategic locations should be increased. During the winter months, areas can be burned to limit the availability of highly flammable fuel during the next hot summer,' explains Johan Sjöström.
Although controlled burning is used to create firebreaks in southern Europe, Sweden relies on other methods to reduce fire risk.
The cheapest and most effective method is to leave a certain proportion of birch trees standing during the thinning process. Pine forests with some spruce are the most fire-prone. Even a small amount of birch can significantly reduce their fire risk. 'If every tenth tree in the forest is a birch, the fire risk decreases by a third,' says Johan Sjöström.
The great thing is that forest owners don't need to do anything to achieve this effect. Birch trees always find their way into the forest via airborne seeds, so you just need to use the brush cutter a little less.
The risk of fire is reduced by a third if every tenth tree in the forest is a birch.
RISE maps and analyses forest and grass fires
Another way to reduce the risk of forest fires is to create barriers of deciduous trees along roads by allowing birch trees to grow in ditches. This enables the emergency services to stop fires from spreading to more flammable coniferous trees from the road.
RISE has extensive knowledge of forest and grass fires. Johan Sjöström and his research colleague, Frida Vermina Plathner, assist various authorities in producing documentation such as reports that map trends and patterns relating to forest and grass fires in Sweden.
We can also produce risk maps and vulnerability analyses for specific areas, such as a municipality. Currently, municipalities primarily allocate resources to their emergency services to enhance firefighting capabilities, which is understandable. However, Johan Sjöström notes that there is much to be gained from preventively limiting the flammability of the ground.
Who will pay for changes to land use in order to adapt to climate change?
‘We already have quite strict legislation in place. Following storms, landowners must clear fallen trees to minimise the risk of spruce bark beetle infestation. After felling, the land must be reforested. To increase the proportion of deciduous trees, we could introduce a rule on tree species composition, as already stipulated in FSC environmental certification,” argues Johan Sjöström.
Economic instruments can also be used to reduce the risk of fire. The authorities currently provide support for the restoration of wetlands. Similar support could be used for the aforementioned deciduous tree barriers.
'It is, of course, impossible to say how big the fire would have been without preventive measures, but we do know that adapting land use to climate change is both cheap and effective,' says Johan Sjöström.
