Changes of soil fauna along the non-native tree afforestation chronosequence on Loess Plateau

Aims: Robinia pseudoacacia is the main non-native tree species that has been widely planted in the Loess Plateau (LP) for revegetation. Most studies focused on its effects on soil and plant properties, but few works investigated biodiversity, especially soil fauna. Methods: We investigated soil fauna in areas where R. pseudoacacia was planted 10, 20, 30, and 50 years ago and grassland areas in LP. Results: Results showed that afforestation can significantly increase the soil fauna groups of the litter layer which does not further increase with forest age. However, the number of soil fauna groups, especially the dominant groups (mites and springtails), was not significantly affected by afforestation. After afforestation, soil fauna abundance first increased and then decreased, with a maximum value observed 20 years post-planting. The average abundance of soil fauna in the soil layer of the R. pseudoacacia was 22, 292 individuals m^–2, which was 4.91 times more than in the litter layer. However, the number of soil fauna groups in the soil layer (10) was significantly lower than that in the litter layer (17). Litter thickness and soil total nitrogen contributed the most and explained 34.7% and 29.5% of soil fauna communities in the litter and soil layers, respectively. Conclusions: Our findings suggest that the change of soil fauna community in the litter layer by afforestation was greater than that in soil layer. However, the effect of forest age on soil fauna was only weak. Afforestation-induced changes in soil and vegetation properties (e.g. stand density, litter thickness, and soil total nitrogen) were crucial determinants of the changes in soil fauna community.