Differential responses of ecosystem services and their trade-offs to environmental gradients in mountainous areas

Mountain ecosystems are functionally diverse and have concentrated environmental gradients. Exploring the changing characteristics and trade-offs of ecosystem services (ESs) under different environmental gradients is beneficial to the conservation and sustainable use of mountain resources. This study evaluated the spatial-temporal changes of habitat quality (HQ), soil conservation (SC), water yield (WY), water purification (N output load) and net primary productivity (NPP) in the Qilian Mountains from 2000 to 2018, and analyzed their responses to environmental gradients. On this basis, the trade-off intensity of ESs and its differential responses to environmental variables are explored. The results showed as follows: 1) HQ, SC, WY and NPP increased significantly, N output load improved slightly. There are significant differences in the spatial distribution of ESs, and ecological land provides these ESs at a higher level than other lands. 2) HQ, WY and NPP have obvious responses to elevation and precipitation, fractional vegetation cover has a greater impact on HQ and NPP, slope has the greatest impact on SC. 3) Except for N output load, there was a synergistic relationship between paired ESs. The low values of the trade-off intensities of the five ESs were in the middle and high-altitude areas with abundant precipitation, higher slope and better vegetation coverage. 4) From 2000 to 2018, the overall benefits of ESs were increased, and hotspots of ESs supply increased and concentrated in the southeast of the study area. This study can provide a theoretical basis for the optimization and management of ESs in mountainous areas.