THE EFFECT OF FIRE ON COLLEMBOLAN POPULATIONS OF MATA DA MARGARACA (PORTUGAL)

A monthly sampling programme was carried out in 1989-1990 in order to analyse the effects of severe fire on edaphic populations of Collembol a in the protected area of Mata da Margaraca. Three sampling stations were established in the most intensely burned area, taking into accoun t the dominant plant species: Quercus robur, Castanea sativa and Vibur num tinus. Three other corresponding stations with the same plant spec ies were selected in the unburned area, for comparative purposes. Biot ope description was achieved through chemical and physical analysis of the litter and soil upper layer. Flucuations of abiotic nature were o bserved, namely in the temperature, water content and pH levels of the burned sites. These alterations are primarily associated to the absen ce of a litter layer with the corresponding loss of thermostable prope rties and moisture holding capacity. The study of the collembolan comm unities structure, by means of agglomerative cluster analysis and the application of a similarity coefficient among sampling stations, puts in evidence approximate values of specific richness for all population s, with the burned sites presenting higher densities and a slight decr ease in the number of species. Certain species of Collembola associate d either to burned or unburned stations were also identified, as well as the exclusivity of a few species to a certain site.