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Abstract：UDdefstanding strearn flow and sediment nmoff is essential in tryhlg to mahltahl

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： Although willows are generally believed to expand population through seed dispersal ， there have been some incidents in which a 】 ternative rnetbod for expansion was clearly used ． In this study ， the authors aimed to under − stand a " seed − ffee " method of willows reproduction ， Observations of two s ple populations suggest that wi 且 lows may reproduce and establish new populations in unoccupied sites through branch propagation ， a clonal reproduction process by rootilg of deposited branches ． As we examined the environmental factors which allowed the new estab − Iishments and the vegetation growth， in those sites where accumu ］ ated gravel particleg ． were relatively larger had higher皿 umber of individuals ploduced f 士 ol皿 deposited branches instead of growing from seed ． 1皿 additio 皿 ， larg 巳 branches may have greater chances ofsurviva 且 which may also be an advantage 飴 r healthier growth with this type of reproduction ． These results suggest that wiUews may be able to expa 皿 d populations by branches floated f ｝ om up − stream ， 働 躍 0 痂 ' 肪 〃OWS ； Pro ρ agation ； Clona〃 e ρ roduct ' 0 η厂Branc 乃， ' Float； Est α biish JOURNAL OF RAINWATERCATCHMENT SYSTEMS ／ VOL15NO ． 12009■ 41