RESUMO
In the pre-Saharan region of Djelfa (Algeria), the coleopteran and spider communities are compared between two neighbouring ecosystems, the one kept as a steppe, the other one reforested with Aleppo pine. In three plots in each area, pitfall (Barber) traps were sampled monthly during one year and arthropods were identified and counted. Two thousand five hundred and fifty-seven individuals, distributed into 95 species, were collected, belonging to four coleopteran families (Carabidae, Scarabaeidae, Tenebrionidae, and Curculionidae), and 14 spider families. The Tenebrionidae (43% of the species and 87% of the individuals) were clearly the most represented group of insects, numerically because of the considerable abundance of Pimelia mauritanica in the reforested area, where this species accounted for half the total number of catches. Among the spiders, the Gnaphosidae represented 40% of the individuals and one-third of the species. The total species richness of the two areas was the same, but, considering the total number of collected species, individual abundance and diversity indexes (Shannon, Simpson) were lower in the reforested zone. However, these parameters became fully comparable when excluding P. mauritanica from the calculations. Without P. mauritanica, numbers and species richness of Tenebrionidae were similar in both areas. Curculionidae had higher populations and higher species diversity in the steppe area, while Scarabeidae were equally abundant in the two ecosystems types. The number, the species richness, and the diversity indexes of Carabidae were much lower in the reforested area than in the steppe one. The opposite was observed with spiders. Nevertheless, more or less important variations in the number of individuals, in one or another direction depending on the species, existed among each taxonomic group. It is concluded that reforestation has not changed biological diversity, but has induced dramatic modifications in the organisation and functioning of the arthropod communities.
