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

Selected water regime indices are used to describe the tolerances to flooding and exposure of littoral and floodplain plants of the River Murray, South Australia. The cover and abundance of 26 perennial species were surveyed at 12 sites along a reach where water levels were influenced by weir operations. Six indices were measured: days when water depths were ≥0, 0–20, 20–60 and ≥200 cm; days when plants were exposed 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 ≥100 cm. Five species clusters were apparent, these being common floodplain species (e.g. Muehlenbeckia florulenta), uncommon floodplain species (e.g. Eleocharis acuta), species from the infrequently flooded littoral (e.g. Bolboschoenus caldwellii), species from the permanently flooded littoral (e.g. Vallisneria americana) and widespread, common species tolerant to flooding and exposure (11 species, including Phragmites australis, 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 exposure. Preferred water regimes are summarised using minimum and maximum values and quartiles for the six indices, and similarities between preferences are illustrated by a model based on minimum spanning tree techniques. Copyright © 1999 John Wiley & Sons, Ltd.