Effects of different restoration measures and sand dune topography on short- and long-term vegetation restoration in northeast China

Our study investigated the effects of different restoration measures and sand dune topography on vegetation restoration in the Horqin Sandy Land, China. We conducted a vegetation survey at different topographic positions on sand dunes at four different types of restoration sites (i.e., grazing-exclusion, shrub-planting, pine-planting, and poplar-planting sites) with restoration periods of ≤35 years and two control sites (i.e., shifting sand dunes and fixed sand dunes). We found a restoration trajectory, starting from shifting sand dunes and aligning all the sites in chronological order. Five restoration phases were identified by distinct species composition in the trajectory. The planting of trees progressed vegetation restoration faster than livestock exclusion and the planting of shrubs. The planting of trees restored shifting sand dunes to the same level of fixed sand dunes after 25 years. Thirty-five years may restore shifting sand dunes to a near-stable state characterized by Cleistogenes squarrosa. We found sequential turnover in species composition along the upward topographic gradient throughout the restoration trajectory, indicating that vegetation restoration on sand dunes is promoted by a process where diaspores establish and spread upward from interdune lowland. Our study provides ecological foundations and suggestions for developing and implementing practical restoration programs in the sand dune area.