Coastal Restoration Trust of New Zealand

Coastal Dune Ecosystem Reference Database

Growth and habitat of Sebaea ovata (Gentianaceae) in New Zealand and Australia DOC Publication

Champion, P.D.; Hofstra, D.E.; Auger, M.E.; Gemmill, C.E.C.
Journal / Source
Science for Conservation
Publisher / Organisation
Department of Conservation
ephemeral, wetland, weed invasion, soil and plant nutrient concentrations, hydrology, endangered plants, sand dune, management options
Ephemeral wetlands are characterised by seasonal fluctuations in water level, with alternating wet and dry periods. The resulting indigenous vegetation is low in stature, making these wetlands vulnerable to alien weed invasion, and many ephemeral wetland plants are now uncommon or endangered. This study investigated soil nutrients and hydrology as potential influences on the susceptibility of dune ephemeral wetlands to weed invasion. Study sites were selected in dune systems on the Pouto Peninsula, Northland, and at Hawkens Lagoon and Whitiau near Wanganui, North Island, New Zealand. At these sites, soils and vegetation were sampled and water tables measured to establish water level fluctuation patterns. Transects were established and vegetation type and percentage weed cover on them were measured on three occasions from 2002 to 2005. Soil nutrient levels did not appear to influence the distribution of alien weed species. The cover of alien species did not increase at Pouto sites over the three monitoring years. However, the Wanganui sites progressively became weedier, and taller indigenous vegetation displaced low-stature turf communities. Weed invasion appears to be promoted by a combination of altered hydrology reducing both the water level and the extremes of wet-dry fluctuations, along with stabilised dunes that restrict the dynamic sand movement that creates and destroys these ephemeral wetland areas. Management options include maintaining natural dune processes which ensure that the conditions for creating new ephemeral wetland areas continue, surveillance for and removal of invasive weed species and, at sites where dunes have been stabilised, removal of taller alien and indigenous vegetation by mechanical methods, grazing or selective herbicides.