High relief yield strong topography-soil water-vegetation relationships in headwater catchments of southeastern China
Xiaole Han, Jintao Liu, Xuhui Shen, Hu Liu, Xiaopeng Li, Jie Zhang, Pengfei Wu, Yangyang Liu
Abstract
Topography strongly controls soil moisture redistribution in forested mountain catchments. However, how terrain-related moisture regulates the distribution of Moso bamboo (Phyllostachys edulis) remains unclear. In this study, we addressed the occurrence and distribution of Moso bamboo by examining terrain-related soil water dynamics at the Hemuqiao Experimental Station in southeastern China. The study was initially conducted on a steep 0.31-ha hillslope. Detailed topography, runoff, and high frequency (6-min) soil moisture data were collected. Both linear (all-possible-subset regression model) and nonlinear (artificial neural network) data mining algorithms were used to build soil water prediction models to investigate the relationships between topography and vegetation. We found that the Moso bamboo distribution changed along the hill-to-valley drainage. There were few Moso bamboo trees in the valley bottom owing to the prevailing waterlogging, while Moso bamboo could hardly penetrate the hilltops and ridges owing to the insufficient water content. We highlighted the importance of lateral unsaturated flow driven by steep slopes in redistributing soil water during summer droughts: it accelerates soil moisture drying on ridges but maintains high moisture content in the valley, resulting in the present pattern of bamboo distribution. We then surveyed the vegetation throughout the 135-ha Hemuqiao catchment and counted individual bamboo trees using remote sensing with unmanned aerial vehicles (UAVs). We found that the Moso bamboo distribution was highly related to water transfer processes. For example, the boundaries of Moso bamboo and mixed forest corresponded well with the locations where water transfer related terrain attributes, such as upslope accumulated area (UAA) and topographic wetness index (TWI), abruptly decreased. In addition, by comparing our site to other sites with different climate-terrain combinations, we found that topography appears to be less important for vegetation distribution only at sites with low relief and dry climates. Finally, based on our understanding of topography-vegetation relationships and the high-resolution Moso bamboo maps we created, we highlighted some practical forest management strategies, such as how to select potential sites for Moso bamboo plantings, and intercropping Moso bamboo with other crops to maintain soil fertility and productivity.