Coastal Restoration Trust of New Zealand

Coastal Dune Ecosystem Reference Database

Distribution of invasive plant species in the sand dunes of Kaitorete Spit, Canterbury Technical Report

Konlechner, T.M.
Publisher / Organisation
Department of Geography, University of Otago
Prepared for Department of Conservation This report updates the distribution of exotic plant species in the sand dunes of Kaitorete Spit. It has been 10 years since the first survey of tree lupin, marram grass, iceplant, gorse, boxthorn and pine (Hilton et al. 2006a). The Department of Conservation has been active in managing these species on the Spit, along with several other non-native plant species since this report. The location of these six species plus four others considered to threaten the conservation values of the Kaitorete dunes (horned poppy, Californian poppy, purple groundsel and broom) were mapped using field surveys in October 2015, supplemented by aerial photographs. Changes in species distributions since 2005 are reported, and the efficacy of DOC weed control works evaluated. Recommendations for the future control of the target species are provided. The target weed species were found the length of the Spit, but were, in general, more common in the western half of the Spit and near Birdlings Flat. The cover of the target weed species remains relatively sparse, with plant communities dominated by indigenous dune species. Lupin is the only surveyed species to have formed a semi-continuous cover over a large portion of the Spit. The remaining target weed species were typically found as small populations and isolated individuals. Many of the surveyed species, however, showed signs of active invasion and range expansion. The DOC control works over the past decade have probably been critical in maintaining the relatively low levels of weed invasion at Kaitorete. The density and distribution of most of the weed species examined in the present study has declined since 2005. Significant populations of most species still remain, largely due to persistent and long-lived seed banks and non-controlled populations that serve as a source of propagules. All of the weed species examined in the current study remain a priority for control, but future control programmes can be designed to target multiple species because of the overall sparseness of the weed species along most of the Spit. Finally, it is recommended that that regular and systematic monitoring be implemented to measure the effectiveness of the operations in removing target weed species, as well as the recovery of desired ecological and geomorphic properties.