Net aerial primary productivity, litter production and decomposition of the reef Phragmites communis in a nature reserve in Hong Kong: management implications

Mean net aerial primary productivity of Phragmites communis (L.) Trin.amounted to 2198.3 f 416.7 g dry wt m-' yr-' (8.24 f 1.56 X 10' kcal m-' yr-l) in the Mai PO Marshes, a nature reserve for migrant birds in Hong Kong.Success of P. con~rnunis is also reflected by the high mean aerial standing blomass of 1250.5 f 309.3 g dry wt m-' and > 50 % area1 coverage increase over a 2 yr period.Litter production was estimated as 504.9 f 212.7 g dry wt m-' yr-' Export of litter was only 0.06 % of production; the bulk of litter was thus accumulated and decomposed in situ.Decomposition of litter was influenced by temperature and inundation regimes, the rate at 52.5 % air exposure being significantly higher than at 13.5 and 2.5 % exposure.Cumulated day-degree and cumulated immersion time were better predctors of decomposition rates than time alone.Higher decomposition rates at intermediate exposure were probably related to phylloplane algal growth, which gave the litter very low C:N ratios, attracting grazing gastropods.Success of P. communis is probably related to the high accretion rate and to traditional management practices which are complementary to the seasonal growth cycle.Rapid spread of the reed may decrease the open area available to waterfowl and their prey, and may also encourage further accretion.Clipping at peak biomass in autumn coupled w t h hydropenod and water level management are possible natural ways of control.