EFFECTS OF INTRODUCED EXOTIC TREE SPECIES ON COLLEMBOLA COMMUNITIES -THE IMPORTANCE OF MANAGEMENT-TECHNIQUES

Studies of the impact of the substitution of autochthonous forests by plantations of exotic tree species (a quite common phenomenon in South ern European countries) on soil arthropod communities (mainly Collembo la and Acarina) generally deal with the effects of the exotic species per se and disregard the management techniques used. In this study the impact of the introduced Eucalyptus globulus on the Collembola commun ities of Quercus ilex ballota and Quercus suber stands was analysed. S ince the autochthonous tree species are similar (in terms of leaf type and the ability to produce litter) the main objective was to examine the effects of the different management techniques used in the two pla ntations of Eucalyptus. (i) There is a significant difference in manag ement techniques used in the Eucalyptus plantations leading to differe nces in habitat configuration: the plantation associated with the Helm -Oak stand is used for cellulose paste production, with periodic remov al of the shrub and herbaceous layers; the other plantation, close to the Cork-Oak stand, is not managed at all, presenting an abundant shru b layer. (ii) in both cases, the substitution of the Oak species by Eu calyptus caused a disruption of the Collembola communities, although i t was more pronounced in e. ilex ballota vs E. globulus (station 1) th an in e. suber vs E. globulus (station 2). The number of individuals, the number of taxa and diversity parameters are in most cases greater under Oak species but more evident in station 1. (iii) Given these res ults, the influence of the factor ''management technique-habitat confi guration'' in analysing and interpreting effects of exotics on soil ar thropod communities is discussed.