Topography alters the optimum timing of peatland initiation across Northeast China during the Holocene

Peatlands are a key carbon sink and play an important role in the global carbon cycle and climate change. Understanding the process of peatland initiation is essential to understand the carbon sink functions of peatlands. While the climate is widely recognized as the main driver that controls the peatland initiation, the importance of topography, a limiting factor that influencing local climate conditions, is still unclear. Here, we used data from 231 peatlands in Northeast China to evaluate the role of topography on peatland initiation. The results show that most peatlands that initiated during the Late Holocene was distributed at elevations <200 m (51 % of sites) and slopes <5 degrees (44 % of sites). The optimum timing of peatland initiation is delayed with increasing elevation and slope, and the potential reasons we speculated is that the increasing elevation slows vegetation growth owing to the decrease in temperature. In addition, steeper slopes are not conducive of water retention. There was little effects of slope aspect on peatland initiation, most likely because variations in solar radiation under various slope aspects may not have a substantial impact on local environmental factors. This study demonstrates that elevation and slope are more important than slope aspect on the frequency and optimum timing of peatlands initiation in Northeast China during the Holocene.