10 questions on forest fires for PD Dr Kirsten Thonicke (geoecologist at the Potsdam Institute for Climate Impact Research and the University of Potsdam) & Dr Till Francke (hydrologist at the University of Potsdam)

1. What causes forest fires? Are all forest fires man-made?
   Although there are natural causes of forest fires, such as lightning strikes and volcanic eruptions, most forest fires are caused by humans. This includes carelessness, e.g. discarded cigarette butts, but also arson or deliberate burning in other parts of the world. Special cases such as the spontaneous combustion of old ammunition also play a role here in Brandenburg.
    
2. How many forest fires are there in Germany each year?
   In Germany, the average number of forest fires per year since the early 1990s has been around 1,000 to 1,150 fires annually. However, depending on weather conditions (especially drought), the number can be slightly higher or lower. For example, 2022 was an extreme fire year (2,397 fires), while only around 560 fires were recorded in 2024.
    
3. What determines how quickly such a fire spreads?
   Terrain, weather conditions (wind, dryness, air temperature), humidity and the composition of dead and living biomass, which then serve as a fuel supply, influence the speed at which forest fires spread. Fine litter such as dry leaves, pine needles, small branches and, in particular, dry grasses contribute to the rapid spread of fire. Only the latter can be influenced by humans – to a limited extent – e.g. through forest management or forest conversion.
    
4. Which types of forest are particularly susceptible to forest fires?
   The composition and structure of the potential fire load play a major role in flammability and fire spread. Coniferous forests are considered particularly vulnerable due to their resinous wood and often considerable litter layer. In addition, management practices (stand density, undergrowth, litter layer, access roads and aisles) can play a major role. In general, monocultures with trees of the same age, such as pine, are considered to be at high risk of burning down across the entire stand before they are thinned out to form large stands. Later, a lot of light reaches the forest floor through the open tree canopy, but usually only a highly flammable layer of grass grows on the predominantly sandy soils, which promotes surface fires. Deciduous forests or even mixed deciduous and coniferous forests have a better microclimate. Deciduous trees store more water in their trunks, branches and leaves, which helps to slow down the spread of fire. Even a higher proportion of deciduous trees in the lower tree layers, as is now more common in Brandenburg due to forest conversion, increases the proportion of herbaceous plants on the forest floor, which also reduces the risk of fire spreading.
    
5. What consequences do forest fires have for society?
   Firstly, there are immediate consequences due to the direct threat to settlements and transport routes, but also the effects of smoke pollution. Immediately after the fire, there is usually increased leaching of nutrients and sediments, which can affect groundwater and water bodies. In the medium and long term, the destroyed forest can no longer fulfil its functions for recreation, climate regulation, timber production and CO₂ storage.
    
6. Are there natural protective mechanisms against forest fires?
   Individual plant and fungus species have adapted specifically to forest fires and can produce fire-resistant seeds or even only grow on burnt areas. However, there is no real protective mechanism – apart from the varying susceptibility of different types of forest, as already mentioned.
    
7. Are we already seeing climate change leading to more forest fires in Germany? What can we expect in the future?
   Here in north-east Germany in particular, climate change is manifesting itself primarily in higher temperatures and more pronounced dry spells. Both of these factors exacerbate the drying out of forest vegetation, to the point of killing it off. In addition, increased occurrences of tree pests or fungal diseases can further weaken tree health and create large areas of dead stands, which in turn are particularly vulnerable or can pose additional difficulties during firefighting. There is no concrete evidence yet that climate change is already leading to more forest fires in Germany. In the future, we can expect the forest fire season to last longer and the number of days with extreme forest fire danger to increase. As a result, we can expect more extreme forest fire situations, which will pose new challenges for forest firefighting, as fire behaviour changes very quickly under extreme heat and wind conditions. 
    
8. What strategies exist for detecting forest fires at an early stage?
   The German Weather Service provides a comprehensive assessment of the risk of forest fires with its forest fire danger index. Together with the well-known locally designated forest fire warning levels, this helps to determine preparatory measures and any necessary restrictions. In Brandenburg, the FireWatch system with sensors for automated smoke detection has been in place since 2001, replacing the conventional person-based monitoring from observation towers.
    
9. How should forests be managed/treated in future to reduce the risk of forest fires?
   For the reasons mentioned above, pine monocultures are considered particularly vulnerable to fire in our region and have long been the focus of forest conversion to more structured and species-rich mixed forests, although this is not the only reason. The more our forest vegetation changes as a result of climate change, the more important it becomes for us to learn from forest fire management practices in Mediterranean countries, for example, which have traditionally been struggling with these problems for a long time. Special measures such as munitions clearance can provide further relief for affected areas. 
    
10. What should I personally pay attention to in relation to forest fires?
    The number one cause of fires is still humans. Every child learns the correct rules of conduct: no open fires and no smoking in the forest. Campfires should only be made in designated areas outside the forest, and these must then be thoroughly extinguished with water to prevent embers from becoming a smouldering source of fire. It is also still far too common to see cigarette butts being thrown out of car windows. Unfortunately, it is rarely possible to have a clarifying conversation in this situation. In any case, we need to be more sensitive in our treatment of nature in order to prevent forest fires during long dry spells or heat waves by being more vigilant.