Trade-off analyses of multiple ecosystem services by plantations along a precipitation gradient across Loess Plateau landscapes

Trade-off is defined as a situation where one ecosystem service (ES) increases while another decreases. In a broader sense, trade-off also refers to unidirectional changes with uneven paces or rates in ESs. Although trade-off analysis for multiple ESs is more integral for ecosystem assessment and management, studies regarding trade-offs are rare in the literature, especially at the landscape scale or across large environmental gradients. Here, we evaluated the co-variations of multiple ESs of black locust (Robinia pseudoacacia) plantations along a precipitation gradient (400-650 mm) on the Loess Plateau using a quantitative trade-off approach. The multiple ESs had complex relationships, with significant regional variations along the gradient. Aboveground carbon, soil organic carbon (SOC), soil total nitrogen (STN), and soil water content (SWC) showed increasing trends with precipitation, but understory plant diversity (UPD) did not. The highest trade-offs were between UPD and SWC and the lowest trade-offs were between SOC and STN among all of the ES pairs. The differences in the trade-offs of varied ES combinations could be the result of unique competition relationships, mass allocation strategies, and time lags. Stand age appeared to be another critical variable in determining the values of ESs and their trade-offs along the precipitation gradient. The decreasing SWC with stand age indicated that the gaining of the other ESs was at the cost of SWC consumption. Because multiple ESs and their trade-offs exhibit high spatial variations across the landscape, spatially explicit management is needed to maintain the benefits while mitigating negative impacts in this water-limited landscape.