Fine-scale spatial patterns of Stellera chamaejasme population in degraded alpine grassland in upper reaches of Heihe, China Trade-off between height and branch numbers in Stellera chamaejasme on slopes of different aspects in a degraded alpine grassland Plant size differences with twig and leaf traits of Zygophyllum xanthoxylum in the northern slope of Qilian Mountains, China Vertical distribution and diversity of butterflies in the northern slopes of Qilian Mountains and Hexi Corridor