## 1 Introduction  
Forest ecosystems have an important role as carbon sinks. The amount of CO\({}_{2}\) uptake by forest ecosystems is known to be affected strongly by disturbances such as logging, fire, herbivory, and windthrow. Such disturbances most likely shift forests from a sink to a source of CO\({}_{2}\) because the uptake of CO\({}_{2}\) from the decreased gross primary production (GPP) is less than the corresponding losses of CO\({}_{2}\) from plant respiration and the decomposition of detritus [1; 2; 3]. After disturbances, the net CO\({}_{2}\) emissions decrease gradually as vegetation recovery progresses. Over time, these disturbed forests become a carbon sink because the increased GPP more than compensates for the corresponding losses of CO\({}_{2}\)[1; 3; 4]. Of all the carbon balance components, the amount of plant biomass plays an important role in the ecosystem carbon cycle because it contributes greatly to the carbon stock [5; 6] and because it affects ecosystem productivity [7]. Carbon sequestration not only occurs in plant biomass, but also in soil organic matter derived from this biomass through litter supply. Therefore, although plant biomassaccumulation is part of the carbon dynamics in forest ecosystems because of the large contribution of soil carbon to forest carbon dynamics, elucidation of biomass accumulation and NPP change during early secondary succession is crucially important for the evaluation of carbon sink/source activities, and the prediction of carbon dynamics of the future [8]. Growing concerns exist about how forest carbon dynamics may be influenced by the acceleration of large-scale disturbances of forest ecosystems by global warming and human activities such as forest fires [9; 10], as well as strong tropical storms [9; 11; 12], insect herbivory, and pathogen damage [13]. Elevated atmospheric concentrations of CO\({}_{2}\) and the resultant climate warming can accelerate the recovery of ecosystem carbon uptake [14]. In addition, vegetation change caused by human-mediated invasive species can affect the ecosystem carbon pool size and carbon balance [15; 16]. Strong interactions also occur between natural and anthropogenic environmental changes. Quantitative evaluation of biomass change associated with the disturbance-recovery regime of forest ecosystems is crucially important to understanding and predicting ecosystem carbon dynamics on both local and global scales [6; 17]. When a stand-replacing disturbance occurs, the environmental conditions of the forest floor change. Subsequently, ground vegetation (herb and shrub layers) contributes substantially to total biomass accumulation [18] before canopy closure. Furthermore, saplings of arboreal species face competition with the ground-covering species. Actually, understory vegetation often suppresses sapling growth through dense shading [19], competition for water and nutrients [20; 21], and alleopathy [20; 22], and influences the speed of forest recovery and biomass accumulation. In Japan, it is often reported that the undergrowth of _Sasa_ (dwarf bamboo) expands after severe forest disturbances [3]. Previous reports showed that the dense shade of _Sasa_ inhibits the growth of saplings [19; 23], while, in sites without _Sasa_, sapling growth would not be as inhibited by shade and forest (biomass) recovery would be expected to be fast, if not inhibited by other factors. In Japan, there are no reports on the monitoring of biomass recovery in sites without _Sasa_. In fact, few studies have examined how biomass changes during the early stage of secondary succession for more than five consecutive years [24]. Long-term changes in biomass accumulation and carbon balance components after severe forest disturbance have been evaluated in temperate and boreal regions using a chronosequence approach, comparing biomass or carbon balances among sites with a different disturbance history [1; 4; 25; 26; 27; 28; 29]. This approach is effective for clarifying long-term changes of carbon dynamics.