EFFECTS OF EDAPHIC FACTORS AND FLOOD FREQUENCY ON THE ABUNDANCE OF LIGNUM (MUEHLENBECKIA-FLORULENTA MEISSNER) (POLYGONACEAE) ON THE RIVER MURRAY FLOODPLAIN, SOUTH AUSTRALIA

Lignum is a native woody perennial which forms extensive thickets in low-lying areas of the floodplain of the lower River Murray, although its range and abundance have been affected by land clearance, salinisation, flow regulation and possibly grazing on seedlings. Comparisons between lignum cover and edaphic data for three sites (Chowilla, Morgan and Overland Comer) showed a negative correlation with soil hardness. Cover was also correlated positively with soil moisture and negatively with time since last flooded, but not correlated with flood recurrence interval. Principal Components Analysis revealed a complex component, loaded by moisture, salinity, pH and organic content, that explained most of the variation in lignum cover. A greenhouse experiment indicated that the salinity and volume of water supplied to plants have significant effects on stem growth. Stands of lignum may be best maintained by flooding low-lying areas every 3-10 years or areas with saline soils more frequently.