The effects of wildfire on ground-active spiders in deciduous forests on the Swiss southern slope of the Alps.
The influence of fire upon biodiversity has been investigated in many ecosystems under a wide range of environmental conditions. However, there is no information on how fire affects faunal biodiversity in deciduous forest ecosystems prone to winter fires, such as those on the southern slopes of the Alps. The main aim of this study was to analyse the effects of single and repeated fires on the structure and species diversity of spider communities in chestnut forests in southern Switzerland. A second objective was to interpret the ecological response of forest-floor habitats to wildfires, using epigeic spiders as bioindicators. One-hundred and thirty-three spider species were found in pitfall trap samples collected between April and September in burnt and control sites in chestnut coppices. Species richness and community composition were influenced by fire frequency and the time elapsed since the last fire. About 19% of the species were trapped exclusively in sites that had been repeatedly burnt, while 11% occurred only in unburnt coppice. Post-fire development of the spider community was chiefly from individuals that survived in situ. We found no characteristic pioneer species in any of the burnt sites. There were indirect effects of fire on the spider community, through interactions between species arising from the changing environmental conditions following a fire. After a single fire, changes in community composition were only observable during the first 2 years. At sites that had experienced repeated fires, there was a more persistent influence on community composition. These sites were characterized by an increase in species richness and species diversity. The presence of a wide ecological range of species in 'repeated fire' sites was probably due to the mosaic structure of the environment and the wide range of microclimate conditions at the soil surface, with a predominance of xeric conditions. 5. The spider communities of chestnut forests were resilient to disturbance by fire. Both the formerly intensive management of these forests (until the 1950s) and a history of frequent fires that goes back to the Neolithic period have played an important part in the development of the spider community in these forests.