EFFECT OF FLOODING-DRAWDOWN CYCLE ON VEGETATION IN A SYSTEM OF FLOATING PEAT MAT AND POND

The relationship between vegetation and seasonal changes in water level was examined in a system of terrestrializing floating peat mat and pond in a warm temperate zone. The duration of flooding, or drawdown period, is related to vegetation in the mat. The first process of terrestrialization would be the attenuation of floating-sinking movement of the mat and the consequent stabilization of water level. Water level at the time when the movement of the mat was attenuated determined the subsequent vegetation change at the site. Two series of succession according to terrestrialization were recognized, and started from initial conditions of low and high water levels respectively. Habitats in low initial water levels experienced short flooding and long drawdown periods. Species changes in the successional series were: Menyanthes trifoliata-Rhynchospora fauriei-Eriocaulon sikokianum-Sphagnum cuspidatum. Submerged peat was experimentally emerged, and the crowded community of Rhynchospora fauriei and Eriocaulon sikokianum established within one or two years. Appearance of these species was controlled by the water level of the habitats in winter. Another series of species changes in terrestrialization process was: Menyanthes trifoliata-Phragmites australis-Carex thunbergii or Isachne globosa. Habitats of these types of vegetation were in the area with relatively high initial water level (long flooding and short drawdown) when the floating-sinking movement of the mat attenuated. After the temporal paludification, the water level was lowered by the accumulation of peat in the process of terrestrialization.