Forest fires wreak havoc on animals and plants, and communities and transportation infrastructure face an increased risk of erosion and rockfall following a fire. Nevertheless, species soon return to affected areas and their diversity surpasses the level of the previous forest within just a few years.
The rate at which the forest recovers depends on the type and frequency of the fires. With frequent and intense fires, only those species that have adapted to fire − known as pyro-resistant species or pyrophytes − are able to survive. At the same time, fires cause the living conditions in the forest to change, which in turn encourages the proliferation of new species. Following the fire, the temporarily sparser forest structure and improved supply of nutrients offer excellent living conditions for many plants and animals.
Some tree species rejuvenate at an astonishing speed after a fire through resprouting and seeding, which eliminates the need to plant trees in places where they provide no particular protection function. Just a few years after a fire, the number of plant and animal species in the repopulated area of the fire can even exceed that of an intact forest. Knowledge of the positive effects on biodiversity and rejuvenation of the forest can be incorporated into silvicultural practices. The ability to quantify colonisation times helps forest managers to assess when and where different types of structural protection measures should be implemented, which species are most suitable for planting, and how quickly natural reforestation is progressing. Insight into the development of species diversity in areas affected by forest fire are especially interesting and can be incorporated into nature conservation measures.
The start of rockfall and erosion
As important as ecological considerations on the recolonisation of areas affected by fire may be, a forest that has been destroyed by fire is chiefly a safety issue – particularly in the mountain forests of Switzerland. Forest fires tend to rage on steep slopes, which often leads to rockfall even as the fire is still burning. If the leaves and topsoil are consumed by fire, the destabilised stones are set in motion. There are even more serious consequences after the fire: the layer of ash created by the fire is water-repellent, meaning that virtually no rainwater is able to be absorbed by the soil for one to two years. As a result, it simply runs off the surface. This causes erosion, especially in heavy rain. Persistent rain can even lead to debris flows. Structural measures help to prevent rockfall and landslides on severely burned areas.