Abstract: It is currently a topic of active consideration to understand how and why the diversity change at different spatial scales.Such knowledge is critical because the regional diversity (γ) can be generated in different ways to quantify the scaledependent patterns of species diversity and strengthen the conservation and management.In this paper, the species diversity (species richness and Shannon diversity) patterns of [WTBX]Pinus tabulaeformis[WTBZ] plantations in the central Loess Plateau in northwest China were analyzed to determine the relative contributions of α and β diversity to γ diversity by additive partitioning across three different nested spatial scales ([WTBX]i.e.[WTBZ], subplot, plot and site scales).The nonrandom ecological processes which differentiate disproportionately the regional diversity were also examined by analyzing the relationships between environmental factors/spatial variables and species composition using canonical variation partitioning (RDA and partial RDA).The study did reveal a significant role of spatial scales in assessing species diversity restoration function of plantations.Species diversity of both herb and shrub layers displayed the significant nonrandom patterns at all the scales.Species richness increased with the spatial scales, and the contribution of beta richness at the site scale was the highest.While the Shannon diversity displayed a distinct opposite trend compared with the species richness patterns, and the highest contribution to γ diversity was from α at the finest scale ([WTBX]i.e.[WTBZ], subplot scale).The spatial distribution of diversity in [WTBX]P.tabulaeformis[WTBZ] plantations was simultaneously driven by environmental filter and dispersal limitation.However, the relative contribution of these two processes varied with different layers.The spatial process (spatial structured environmental factors and purely spatial variables) was dominant in herb layer, while the environmental filter, including spatial structured environmental factors and purely environmental factors, was dominant in shrub layer.In herb layer, the altitude, slope position, soil organic matter content and soil available potassium content were the main environmental factors; in shrub layer, the altitude, slope aspect, soil available nitrogen content, available potassium content and available phosphorus content were the significantly contributing environmental variables.In conclusion, larger scales drive the overall species richness patterns, while finer scales determine the Shannon diversity patterns, which may be explained by distribution patterns of the common and rare species.These results suggest that the pine plantation alters the plant species composition considerably after a longterm succession and should not be considered as the “green deserts”.High beta diversity at the site scale demonstrates the importance of this scale in preserving biodiversity.However, different measures should be applied to protect the species in different layers with different species traits.