Human disturbance rather than habitat factors drives plant community assembly and diversity patterns in a semiarid region

Human activities may lead to land degradation, and then influences diversity and function of ecosystems. Understanding the plant community assembly processes and diversity patterns along human activities-related gradients are an important facet of ecological research and can be used to reveal vegetation dynamics under land degradation on the Loess Plateau. In this study, we evaluated the net relatedness index, phylogenetic diversity, and species diversity along habitat (elevation, slope, aspect, residential distance, succession time) and comprehensive disturbance gradients on the Loess Plateau, China. We found that community assembly processes were mainly influenced by slope and succession time linked to human activity. Study regions with slope >20 degrees or succession time > 35 years showed no environmental filtering effect during community assembly processes, because these region usually had fewer cropland development activities. Although phylogenetic and species diversity showed a dissimilar pattern along gradients, we also summarized human activities rather than habitat factors drive diversity patterns. In summary, we demonstrate that human activities mainly influence community assembly processes and diversity patterns. With reduction of human disturbance in future, land degradation will be ameliorated on Loess Plateau.