Effects of Soil Amelioration and Tree Planting on Restoration of an Air-Pollution Damaged Forest in South Korea

In order to restore the forest ecosystem in the vicinity of an industrial park, Ulsan, southeastern Korea, which has been heavily acidified by air pollution, a preliminary experiment by applying tolerant plants selected through several procedures, and dolomite and sewage sludge as soil ameliorators was carried out. Furthermore, a restoration based on the results was executed and the effects were evaluated based on the creation of safe sites, where new species can establish: regeneration of the forest with species similar in composition to the natural vegetation of native forests that are distant from the industrial park; increase in species diversity. In a preliminary study, the necessity of soil amelioration was diagnosed. Quercus serrata, Alnus firma and Ligustrum japonicum, which represent for tree, subtree, and shrub layers of vegetation in this region, were used as sample plants. Dolomite, sludge, and a mixture of both materials were applied as soil ameliorators. Bare ground (BG), and two grasslands dominated by forbs (GF) and grass (GG), respectively were designated as experimental plots based on a vegetation map of the corresponding area. BG and GF plots, which have lower organic matter contents, increased the growth of sample plants in response to soil amelioration, whereas that with higher contents, GG plot, did not show this response. The result suggests that necessity of soil amelioration depends on site quality. The effects of soil amelioration depended also on the sample plants. This difference is due to an ecological property of A. firma, which can fix atmospheric nitrogen through a symbiotic relationship with actinomycetic fungi. This result implies that this alder could be used as a substitute for soil ameliorators in restoration plan of this area. The height and standing crop of undergrowth, which forms dense grass mat and thereby impedes establishment of new plants, decreased in the restored stands. Such a decrease in the height and biomass of undergrowth could be recognized as providing safe sites, in which the other plants can invade, by removing the dense carpet formed by Miscanthus sinensis. The results of stand ordination showed a progression of the former bare grounds to either M. sinensis (GG) or Pueraria thunbergiana (GF) stands, suggesting a natural recovery through succession toward the stands dominated by both plants. But the change was not progressed beyond the grassland stage. Active restoration practice, which was carried out by applying tolerant plants, however, led to a change toward species composition similar to the natural vegetation before devastation. Furthermore, restored stands reflected the restoration effect by showing higher diversity than the stands in the degraded state. These results showed that the restorative treatment carried out by introducing tolerant plants functioned toward increasing both biological integrity and ecological stability and thereby could meet the restoration goal.