Natural CO₂ springs in Japan: A case study of vegetation dynamics

To study the effects of elevated atmospheric CO₂ concentration on vegetation dynamics in the natural environment, we measured ground cover across CO₂ gradients at a natural CO₂ spring. Two hollows, one emitting CO₂ and a similarly shaped non-emitting one, were used. Both hollows had been covered with mature beech and oak trees with a sparse understory. In 2000 the vegetation within and around the Hollows was removed, and revegetation began. After four years of revegetation, we established 213 quadrats in the hollows, and measured the ground cover of seven target species (Fagus crenata, Salix bakko, Sasa kurilensis, Carex albata, Carex oxyandra, Scirpus wichurai and Miscanthus sinensis) at each quadrat. The ground cover of each species was analysed as a function of atmospheric CO₂ levels that were interpolated from actual measurements at six locations and depths from the top of the hollow. The abundance of Carex albata and Salix bakko was higher in high CO₂ areas, and Sasa kurilensis was more abundant in the ambient CO₂ area. No significant effect of CO₂ was observed in other species. These results suggest that elevated CO₂ favours the growth and dynamics of some species, and consequently may modify the process of vegetation succession.