Productivity-decomposition dynamics of Typha orientalis at Kaitoke Swamp, Great Barrier Island, New Zealand

Abstract

The productivity and decomposition of Typha orientalis at Kaitoke Swamp on Great Barrier Island, New Zealand, were measured to determine the annual dynamics of its biomass. These interactions, including peat accumulation under nutrient-rich conditions, are often poorly understood. Annual productivity and maximum "standing" above-surface and below-surface biomass were measured using sequential harvest plots. Decomposition was determined using recently dead T. orientalis leaves in mesh litter bags placed on, above, and below the swamp surface. The annual productivity of T. orientalis (c. 3 kg m-2) is within world-wide estimates for swamp wetland species. The order of decomposition of leaf litter at Kaitoke Swamp is: below surface > surface > above surface. Litter bag mesh size did not affect decomposition processes, indicating that larger decomposer animals probably do not have a significant influence on biomass loss in the site. Peat accumulation was estimated based on observations and measurements of the entrainment process. T. orientalis had low estimated peat accumulation, with 6.5% (0.19 kg m -2 yr-1) of the annual production remaining after all components had been underground for 5 years. Consequently a large amount of the annual production of biomass is lost from the site. The ratio of maximum biomass to annual productivity was 2.2, also indicating low biomass accumulation.