Afforestation affects soil seed banks by altering soil properties and understory plants on the eastern Loess Plateau, China

To solve the serious soil erosion problem on the Loess Plateau, large-scale reforestation efforts have been carried out in the past few decades. However, previous studies on the species diversity of these reforestation plantations focused mainly on the aboveground vegetation while ignoring the value of soil seed banks for diversity conservation. An understanding of the determinants of the soil seed banks is particularly lacking. We investigated the compositional characteristics of understory plants and soil seed banks in rehabilitation areas with different vegetation types in the Caijiachuan watershed in Shanxi, China. The results indicated that the understory vegetation and soil seed banks differed significantly among the different vegetation types. The rehabilitation effect of plantations was significantly better than that of naturally restored abandoned farmland, while the selection of afforestation tree species was also crucial. In this respect, coniferous forests (Pinus tabulaeformis) were not as effective as broad-leaved forests (Robinia pseudoacacia) and mixed coniferous-broad-leaved forests in terms of vegetation recovery. In addition, there were significant differences between the composition of the seed bank and the actual vegetation, but the soil seed banks in the plantations may nonetheless contribute to the reconstruction of the aboveground vegetation; the R. pseudoacacia forest and mixed forest showed greater regeneration potential from the seed bank. Afforestation significantly affected the composition and structure of the understory plant and seed banks by altering the understory habitat. Correspondingly, we inferred that afforestation may restrict the development of understory plants and seed banks mainly by regulating soil moisture and canopy density. Therefore, in vegetation communities with high afforestation density or canopy density, measures such as thinning or pruning should be implemented to provide suitable habitat for understory plant growth and seed germination. In addition, most plantations in this area are composed of a single tree species, so we suggest that human interventions to promote the conversion of single-species plantations to diversified or uneven-aged forests should be performed.

Automated summary

Research has shown significant differences in the understory vegetation and soil seed banks among rehabilitation areas with different vegetation types. The effects of plantations are better than naturally restored abandoned farmland, and the choice of tree species is crucial for vegetation recovery.