Fire ecology on the southern side of the Alps in Switzerland: Effect on soil, vegetation and fauna

The region on the southern side of the Alps in Switzerland is the region most often affected by forest fires. Understanding the effect of the fire on the main components of the ecological system (soil, vegetation, fauna) is extremely important in order to plan possible countering measures and provide correct information for specialists and the public. The present contribution provides a synthesis of all that is known today of forest fire ecology in southern Switzerland. At ground level, fire eliminates the biomass on the surface of the soil creating a level of ash, which changes the chemical and physical characteristic of the soil and renders it temporarily impermeable. Subsequent precipitation, especially during the first year following the fire, flows off the surface and increases water erosion. After an initial temporary increase in the number of species, the diversity of the vegetation becomes impoverished for long periods, especially in cases where fires occur repeatedly. If, on the other hand, surface fires occur at only isolated intervals, the vegetation cover experiences no great changes. The fires have diverse effects on invertebrates: following a single occurrence, species diversity remains constant and the community regenerates itself after 6­14 years. The situation is different if repeated fires occur: the number of species increases and is maintained over a period of 17­24 years after the event. The forest invertebrates that profit most from fires are those that live in openings where sunlight can enter: pollinators and predators that find abundant food on the burnt surfaces. In addition, 12 pyrophile species of plants, fauna and fungi have been recorded on the southern side of the Alps, which depend on fire in their reproductional or life cycles. From a practical point of view, the results show that fires threaten the protective function of forests. In order to generate positive effects of the fire on biodiversity, specific management measures are conceivable that promote the various development stages of the forest and thus its diversity. The discussion with regard to pyrophile species remains open in view of their inseparable union with fire.