Abstract:Over-grazing, mining, and inappropriate agricultural management practices combined with repeated drought events in the Mu Us sandy land in northern part of Shaanxi, Northwest China, have caused severe desertification. This landscape-scale degradation has significantly declined the possibility of natural ecosystem recovery. These conditions warrant ecological restoration of these areas to allow the re-development of sustainable ecosystems. Seedling establishment is the most crucial stage in a restoration project. In the Mu Us sandy land, restoration efforts might have been largely limited owing to the soil moisture deficiency, temperature fluctuations, high light intensities, low soil fertility, competition, allelopathy, herbivory, and wind. Several restoration techniques have long been used to alleviate these problems; however, their application has been restricted by low seedling and plant survival as well as high cost. Thus, developing novel, low-cost, and efficient restoration techniques is necessary. Plant-plant interaction effects provided by nurse plants can significantly increase or decrease the seed germination rates and establishment of seedlings under their canopies. Therefore, this study primarily aimed to determine the ability of shrubs to be used as a restoration tool in the Mu Us sandy land. Two-year-old seedlings of Pinus tabulaeformis and Pinus sylvestris were planted under the canopies of three shrub species (Caragana intermedia, Amorpha fruticosa, and Salix psammophila) or in open areas with no shrubs as a control; the objective was to determine whether the presence of shrubs facilitated the establishment of pine seedlings, which was assessed three times over three consecutive growing seasons, in the Mu Us sandy land. The height and canopy spatial area of shrubs were measured. The microclimate conditions (light intensity, air and soil temperatures, as well as soil moisture) were recorded in the four microhabitats, that is, under the canopy of each of the three shrubs and in areas without the shrubs (control). The near-surface light intensity as well as air and soil temperatures were lower under the shrubs, which led to higher soil moisture; because of these conditions, the survival rates of P. tabulaeformis seedlings growing under the canopy of the shrub species were higher than those of the seedlings growing in the control area (P < 0.05). However, the survival rates of P. sylvestris seedlings were higher only under the canopy of A. fruticosa (P < 0.05). The survival rates of P. tabulaeformis and P. sylvestris seedlings were the highest under the canopy of A. fruticosa (P < 0.05). Thus, the exotic species, A. fruticosa, could be used successfully as a nurse plant. Increased plant height and canopy area of nurse shrubs might improve the establishment of pine seedlings. The leguminous shrubs (C. intermedia and A. fruticosa) showed continuous facilitation of seedling establishment during moderate drought stress (summers of 2012, 2013, and 2014), but the presence of a dense and small shrub, C. intermedia, reduced the rate of seedling establishment possibly because of the competition for light. In 2012, S. psammophila also facilitated seedling establishment, but an unknown effect led to a high mortality rate for seedlings growing under their canopy. A noteworthy finding was that the growth of the two pine species was not inhibited when they were planted under the three shrubs. Pine seedlings had the shortest leader shoot lengths in 2012, with light intensity and soil moisture as important factors that controlled their length. The shade-tolerant species, P. tabulaeformis, had a higher seedling survival rate than that of P. sylvestris. In conclusion, nurse-shrub facilitation can be used as an effective restoration strategy in the Mu Us sandy land. However, the successful use of shrubs as nurse plants depends on their origin and morphological characteristics and ecological effects; the selection of target species depends on their tolerance of shade and their interaction with nurse plants.