Influence of Large Seasonal Water Level Fluctuations and Human Impact on the Vegetation of Lake Tonle Sap, Cambodia

Abstract

Lake Tonle Sap, the largest inland water body in Southeast Asia, encompasses unique ecosystems and wildlife adapted to large seasonal fluctuations in water level. The permanent waterlogged area of the lake is encircled by a vast floodplain, the inundated woodland being dominated by Barringtonia acutangula (Lecythidaceae), probably a major vegetation type of this ecotone, although human impact has degraded the floodplain vegetation and developed forest is restricted to a narrow band along the shore in the lowest water season. The aspects of seasonally inundated vegetation (i.e., variations in physiognomy, species composition, stratification, and distribution) on the coastal side of the floodplain (approximately 4 km in depth), located adjacent to the southern part of Siem Reap, was analyzed. Quantitative data for phytosociological evaluation were collected at 67 quadrats (10 m × 10 m each) during the low water seasons in 2005 and 2006, the sampling plots being classified by Two- Way Indicator Species Analysis (TWINSPAN) and ordinated by Detrended Correspondence Analysis (DCA). Two vegetation zones (i.e., extensive cropland and disturbed woodland), seven vegetation types (i.e., “Cultivated field,” “Fallow field,” “Shrub,” and “Tall-shrub” in the extensive cropland zone and “Scrub,” “Open forest,” and “Closed forest” in the disturbed woodland zone), and vigorous invasion and/or regeneration of Barringtonia acutangula over the study area were identified. Human impact (e.g., plowing, burning, and cutting for firewood) seemed to be inversely related to both duration of flooding and maximum water depth and to be the main cause of degradation of seasonally inundated vegetation.