The effect of salinity on the growth of some New Zealand sand dune species

Abstract

Soil salinity affects many coastal communities, but it is not clear to what extent salinity is involved in the distribution of sand dune vegetation. Twenty-nine species (including nine exotic species) found on New Zealand sand dunes were used in a study of root-salinity tolerance. Six concentrations of salt were added to plants grown in water culture; growth rates and the percentage of live material were measured. About half the species were more intolerant of root-salinity than the glycophytic control (wheat). These were mainly native New Zealand herbs and grasses and the introduced species Silene gallica and Lupinus arboreus. Tolerant species included the native species Desmoschoenus spiralis and Scirpoides nodosa. Most tolerant exotic species were grasses; Elymus farctus was the most salt tolerant species tested, and possibly in Barbour's ‘facultative halophyte’ category. Species scores from the first vegetation gradient of an ordination of field data from four dune systems were plotted against results from this study. For some species, root-salinity tolerance correlated with their field position. However, there was little correlation with distributions on West Coast dunes, with some glycophytes growing in the semi-fixed dunes. This was attributable to the high rainfall. On the dry east coast, however, species were more tolerant and their distribution more closely linked to their salinity tolerance. New Zealand dunes contain a mixture of root-salinity tolerant species and root-salinity intolerant species. It is suggested that root-salinity is only one of a complex of environmental factors important on dunes.