Roles of dominant understory Sasa bamboo in carbon and nitrogen dynamics following canopy tree removal in a cool-temperate forest in northern Japan

To clarify the role of dense understory vegetation in the stand structure, and in carbon (C) and nitrogen (N) dynamics of forest ecosystems with various conditions of overstory trees, we: (i) quantified the above- and below-ground biomasses of understory dwarf bamboo (Sasa senanensis) at the old canopy-gap area and the closed-canopy area and compared the stand-level biomasses of S.senanensis with that of overstory trees; (ii) determined the N leaching, soil respiration rates, fine-root dynamics, plant area index (PAI) of S. senanensis, and soil temperature and moisture at the tree-cut patches (cut) and the intact closed-canopy patches (control). The biomass of S. senanensis in the canopy-gap area was twice that at the closed-canopy area. It equated to 12% of total biomass above ground but 41% below ground in the stand. The concentrations of NO3- and NH4+ in the soil solution and soil respiration rates did not significantly change between cut and control plots, indicating that gap creation did not affect the C or N dynamics in the soil. Root-length density and PAI of S. senanensis were significantly greater at the cut plots, suggesting the promotion of S. senanensis growth following tree cutting. The levels of soil temperature and soil moisture were not changed following tree cutting. These results show that S. senanensis is a key component species in this cool-temperate forest ecosystem and plays significant roles in mitigating the loss of N and C from the soil following tree cutting by increasing its leaf and root biomass and stabilizing the soil environment.