We adopted the “space for time” approach to examine the pattern of carbon sequestration in karst forest ecosystems along the natural restoration process. Forest vegetation types representing six typical successional stages were selected and investigated, which include herb stage, herb to shrub stage, shrub stage, shrub to arbor stage, arbor stage, and climax stage. Twenty-four plots of 30 m × 30 m were established on sites of the six forest types, and samples of plants, litter and soil were collected in each plot.

The total vegetation biomass increased from 7.97 to 166.83 t·hm^-2 with advancement of restoration stages, corresponding to the trend of changes in biomass for the arbor layer (from 41.77 to 164.59 t·hm^-2), but with declining biomass for the herb layer (from 8.45 t·hm^-2 at the herb to shrub stage to 0.68 t·hm^-2 at the climax stage) and the shrub layer (from 32.87 t·hm^-2 at the shrub stage to 1.56 t·hm^-2 at the climax stage). The ratio of above ground to belowground biomass in karst vegetation was relatively low (varying between 1.26 and 2.03), especially for the shrub layer (varying between 1.23 and 1.45). The weighted average carbon content increased from 36.76% to 48.74% with the process of restoration. In the process of the natural restoration, the carbon density in the arbor layer increased from 19.44 to 80.40 t·hm^-2, but decreased from 3.19 t·hm^-2 at the herb to shrub stage to 0.23 t·hm^-2 at the climax stage in the herb layer and from 15.13 t·hm^-2 at the shrub stage to 0.69 t·hm^-2 at the climax stage in the shrub layer. The overall carbon density showed an increasing trend from the early stages (herb and herb to shrub stages), through the middle stages (shrub and shrub to arbor stages), to the late stages (arbor and climax stages) at levels of ecosystems (from 15.72 to 99.37 t·hm^-2), vegetation (from 2.93 to 81.31 t·hm^-2), and soil (from 8.26 to 18.80 t·hm^-2), accompanied by a reduction in litter (from 4.97 to 1.53 t·hm^-2). It can be concluded that vegetation, especially the component of woody plants, has the greatest influence on ecosystem carbon stocks during the recovery progress of karst forests, with little effects of soils. Therefore, it is important to facilitate the recovery of vegetation for enhancing karst ecosystem carbon sink.