Floristic variation and environmental relationships of sand dune communities at Kaitorete Spit Scientific Reserve

Abstract

A study of the plant-communities, their abundance, distribution, and environmental relationships, was carried out at Kaitorete Spit Scientific Reserve. The relationships between indigenous and exotic species were investigated and the conservation values of the reserve investigated.

The cover of each species was assessed using 2m x 2m plots, and the environmental factors of soil salinity, soil texture, soil pH, and distance from the sea were measured. Kaitorete Spit Scientific Reserve was divided into 5 blocks, and in each block four transect lines were established. Along each transect line, plots were located at 50 m intervals. The floristic data were analysed using the computer programme TWINSPAN, to derive the plant-communities, and their environmental relationships investigated using the programme DECORANA, as implemented in the programme CANOCO. Plant-communities were mapped.

In the Kaitorete Spit Scientific Reserve, progressive changes in vegetation composition, from the sea inland, were closely related to differences in soil pH, texture and salinity. On the foredunes, where soil texture was sandy and loose with high salinity, the most dominant plant species was pingao (Desmochoenus spiralis), a salt-tolerant species. This species also dominated the inner dunes where soil texture was similar to the foredunes. In the deflation hollows where the soil texture was coarser, with gravels and stones up to 20 cm in diameter, communities were characterised by Raoulia, Scleranthus, and Zoysia. On the inland sandy plain, where soil texture was finest, Rytidosperma dominated, associated with many other grasses. On the old dunes, bracken fern (Pteridium esculentum) and many other tall shrubs dominated.

Kaitorete Spit is one of 30 sites in the South Island and Stewart Island, which are considered to be of national priority for conservation, having total ratings of 15 or more. In terms of conservation values amongst the zones of Kaitorete Spit Scientific Reserve, zone 1 (foredunes) is important because of the dominance of pingao. Zone 3 (inner dune ridge) is also important because of the presence of the endemic native broom Carmichaelia appressa, and species at their southern most limits Muehlenbeckia astonii and Dodonaea viscosa.