Sampling sites C started to be influenced by the spread of vegetation from the stable zone in the first forty days. Brachiaria mutica became the second dominant specie after KyllingabrevifoliaRottb.(Table 2).However,after the fortieth day,Ageratumhoustonianum Mill.became the third most prevalent species,and then it grew in to the most dominant plant after the sixtieth day. This situation resembled the primary flora succession of the flood irrigation zone in a previous study (Lee, 2002).