Tolerance of riverine plants to flooding and exposure indicated by water regime

Selected water regime indices are used to describe the tolerances to floodi ng and exposure of littoral and floodplain plants of the River Murray, Sout h Australia. The cover and abundance of 26 perennial species were surveyed at 12 sites along a reach where water levels were influenced by weir operat ions. Six indices were measured: days when water depths were greater than o r equal to 0, 0-20, 20-60 and greater than or equal to 200 cm; days when pl ants were exposed to greater than or equal to 100 cm of water; and days of longest exposure to water. Ordinations of plant abundances were correlated with the frequency of flooding to 0-20 and 20-60 cm, and exposure to greate r than or equal to 100 cm. Five species clusters were apparent, these being common floodplain species (e.g. Muehlenbeckia florulenta), uncommon floodp lain species (e.g. Eleocharis acuta), species from the infrequently flooded littoral (e.g. Bolboschoenus caldwellii), species from the permanently flo oded littoral (e.g. Vallisneria americana) and widespread, common species t olerant to flooding and exposure (11 species, including Phragmites australi s, Cyperus gymnocaulos and Bolboschoenus medianus). Half of the 26 species occurred in at least four of seven regimes suggested by cluster analysis of water regime indices, thus indicating a broad tolerance to flooding and ex posure. Preferred water regimes are summarised using minimum and maximum va lues and quartiles for the six indices, and similarities between preference s are illustrated by a model based on minimum spanning tree techniques. Cop yright (C) 1999 John Wiley & Sons, Ltd.