Afforestation promotes ecosystem multifunctionality in a hilly area of the Loess Plateau

Over decades, afforestation has been one of the major nature-based solutions to restore degraded ecosystems worldwide. However, a consensus on whether restoration-oriented afforestation is an effective means to maintain ecosystem multifunctionality has not yet been achieved. Here, soil and plant samples were collected among three different vegetation patterns including SH (shrub and herb species), AH (arbor and herb species), and ASH (arbor, shrub and herb species) in our study area after nearly 30 years of Robinia pseudoacacia plantation, to assess the effects of vegetation pattern on ecosystem multifunctionality evaluated comprehensively via the averaging approach and multiple threshold approach. The results showed that vegetation pattern such as ASH had a significant lower soil water content but higher total nitrogen and productivity than SH at the deep soil depth (500 cm soil profile) (P < 0.05), while they had no significant difference in soil organic carbon and total phosphorus. However, there were no significant differences among the above-mentioned five functions between AH and ASH. Additionally, the average multifunctionality index of SH was significantly lower than that of AH and ASH (P < 0.05). A strong positive association between species diversity and multifunctionality was exhibited at thresholds ranging from 22 % to 93 %, and the percentage to realize the maximum diversity effect on multifunctionality was 60 %. Moreover, the slope of the relationship between species diversity and multifunctionality decreased at higher threshold between 62 % and 93 %, indicating that high species richness might not maintain functions at their highest levels. Overall, afforestation after long-term recovery can maintain ecosystem multifunctionality quantified based on water conservation, carbon sequestration, nutrient cycling and productivity. The appropriate improvement of species diversity is conducive to sustainable forest management in a semiarid region.