Effect of desert shrubs on fine-scale spatial patterns of understory vegetation in a dry-land

In arid and semiarid ecosystems, shrubs usually play an important role in determining vegetation pattern and landscape diversity. By exerting multiple effects on microhabitat, shrubs can modulate the performances, species assemblages, and spatial patterns of their understory plants. Both positive and negative interactions act simultaneously, and the balance between them shifts at different spatial locations. To better understand shrub–herb interaction and its possible mechanisms, we chose three common shrub species in a dry-land of Hexi desert region and examine their effects on microhabitat and understory vegetation among different locations. Results showed that the understory vegetation can benefit from the presence of Calligonum mongolicum, as a result of modified drought stresses, increased soil nutrients and more available seeds. However, understory vegetation exhibited better performances at the peripheral location of Nitraria sphaerocarpa patches, which can be explained by the balance between resources improvement and seeds limitation. It has been also found that the higher salt contents (e.g., Na+, K+, Cl−, and SO4 2−) on vegetation patches beneath Haloxylon ammodendron may interfere with herbaceous performances and thus modified their spatial pattern. Our study revealed that the multiple effects of shrubs on microhabitat are species specific and at a fine scale, which may result in various fine-scale spatial patterns of vegetation in response to different shrub species.