Effect of conversion of cropland to agroforestry land versus natural grassland on ground-active arthropods in an agro-pasture zone of northern China

In Yanchi County, Ningxia, belonging to the agro-pasture transition zone in northern China, an investigation on ground-active arthropods was carried out using a pitfall trapping method in response to the conversion of cropland to agroforestry land versus natural grassland. The results showed: (1) there were 25 groups belonging to 7 orders and 23 families. The dominant groups included Aphodiidae and Formicidae families, which comprised 45. 30% of the total individuals. There were 13 common groups occupying 49.17% of the total individuals. The remaining 10 groups were relatively rare, only comprising 5.53% of the total individuals; (2) there were four dominant groups in both crop- andgrassland, whereas only one group (i.e., Formicidae) was found in Populus and Caragana agroforestry land. However, the composition of dominant groups were completely different between grassland and cropland habitats. Meanwhile, the dominance of dominant groups decreased remarkably from 86.67% in cropland to 54.90%, 63.16%, and 61.70% in Populus and Caragana agroforestry land and grassland, respectively. The number of common groups and their dominance increased considerably in response to the conversion of cropland to agroforestry land versus natural grassland. No rare groups were found in these four habitats including cropland, Populus and Caragana agroforestry land, and grassland; (3) there was a significant (P < 0.05) effect of the conversion of cropland to agroforestry land versus natural grassland on group richness and the Shannon index, whereas no significant (P> 0.05) effect was found on the total abundance and Simpson index of ground-active arthropods. The group richness and Shannon index of ground-active arthropods were found to be markedly greater (P < 0.05) in grassland, followed by those in Populus and Caragana agroforestry land, and cropland; (4) the Jaccard index regarding ground-active arthropod communities ranged from 0. 13 to 0. 39, which indicated a dissimilarity between different habitats in cropland, Populus and Caragana agroforestry lands, and grassland; (5) soil moisture and total nitrogen were found to be the key factors driving the structure of ground-active arthropod communities based on the pRDA results. It was concluded that the conversion of cropland to Caragana shrubland and natural grassland could be beneficial for the improvement of soil physical-chemical properties, and the conversion of cropland into natural grassland could indicate a facilitative effect on arthropod biodiversity recovery in the agro-pasture transition zone of northern China.