Productivity‐decomposition dynamics of Baumea juncea and Gleichenia dicarpa at Kaitoke Swamp, Great Barrier Island, New Zealand

Abstract

The productivity and decomposition of Baumea juncea and Gleichenia dicarpa were measured at two sites at Kaitoke Swamp, Great Barrier Island, New Zealand, to determine their annual biomass dynamics. These interactions, including resulting peat accumulation, are poorly understood, especially for wetland sedges. Annual productivity and maximum “standing” above‐surface and below‐surface biomass were measured using sequential harvest plots. Decomposition was determined using recently dead B. juncea culms and G. dicarpa fronds confined in mesh litter bags placed on, above, and below the swamp surface.

The annual productivity of B. juncea (c. 1.4 kg m^‐2) was within worldwide estimates for swamp wetland species, but that of G. dicarpa (c. 0.5 kg m^‐2) was low. The order of decomposition of B. juncea leaf litter was: surface > above surface > below surface; but in the case of G. dicarpa there were no significant differences. Litter bag mesh size did not affect decomposition processes for either species, indicating that larger decomposer animals probably do not have a significant influence on biomass loss. Peat accumulation was estimated based on observations and measurements of the entrainment process. Baumea juncea and G. dicarpa both had high peat accumulation, with 71.6% (0.99 kg m^‐2 yr^-1) and 42.8% (0.22 kg m^-2 yr^-1) of the annual production remaining, respectively, after all components had been underground for 5 years. Consequently, only a small amount of the annual production of biomass is lost from both sites.

Key words:

• annual production
• Baumea juncea
• biomass components
• decomposition
• entrainment process
• Gleichenia dicarpa
• Great Barrier Island
• growth cycle
• peat accumulation