Multiple‐scale assessment of understory herb species diversity in pine plantations after long‐term restoration

Plantations are established for a variety of purposes including wood production, soil and water conservation, and carbon sequestration. However, their implications for species diversity are considerably debated. To assess restoration effect of species diversity in plantations after 50 years’ natural restoration, understory herb species diversity of Chinese pine (Pinus tabulaeformis) plantations were characterized and compared with secondary growth oak (Quercus wutaishanica) forests by additive partitioning across three different nested spatial scales (subplot, plot and site scales) in the middle of the Loess Plateau, northwestern China. Whether these two forest types demonstrate different structuring processes was also examined by quantifying the relative contributions of space and the environment on community composition. Overall, the two forests displayed similar accumulation of species diversity across spatial scales. The contribution of species diversity components increased with the spatial scale, and both forests displayed lower alpha diversity at the subplot scale but higher beta diversity at the plot and site scales. There was no significant difference in alpha or beta diversity between the two forests at any of the three scales, but in species compositions at the subplot and plot scales (p < 0.05). The diversity of both forest types were simultaneously governed by environmental and spatial processes, with the exception of a greater contribution of each component in the secondary growth oak forests, but both forests were dominated by environmental processes. Our study highlight the significant role of spatial scales in assessing the result of biodiversity restoration of plantations. These results suggest that pine plantations function in a similar manner as secondary growth oak forests for understory herb diversity, albeit with different community compositions.