Second stage ecological restoration near Te Roto o Wairewa/Lake Forsyth and Little River, Horomaka (Banks Peninsula)

Abstract

Most revegetation and ecological restoration projects throughout New Zealand are planted with a limited selection of native plant species. Funding restrictions often do not allow additional time for forward planning of longer term plant community diversity outcomes. Little consideration is made for the emergence of beneficial seedlings, or for the planting of later stage species. The aim of this research was to investigate whether expanding the plant species list proposed for a selected planting area would enhance and extend local biodiversity, if understorey plants are included in longer-term planning. One objective was to enhance an existing ecological restoration project by doubling the number of native species with a selection of regionally rare, less common plants, and common plants with limited sale in nurseries. Twenty-one plant species were selected for the study. This research study was carried out in conjunction with the Wairewa Rūnanga. The hau kāinga hapū (the local people belonging to the Wairewa Marae, are Ngāti Irakehu and Ngāti Makō, (sub-tribes of Ngāi Tahu), are based at Little River and Te Roto o Wairewa / Lake Forsyth, Horomaka (Banks Peninsula), in Canterbury. With the support of a Vision Mātauranga award, the project was based near the Wairewa Marae, and at a nearby partially re-vegetated stream terrace. A preliminary study of archival oral and written histories provided a database of regionally rare or less common plants that were once present in this Banks Peninsula landscape. These included plant species of more particular or significant interest to the Wairewa tangata whenua, (the local people belonging to this area), particularly plants used in Rongoā Māori, (traditional Māori healing). A desk study provided an historical background upon which to base a proposed planting list and site location. Sixteen native plant species were already present in wider adjacent areas of the existing project on the stream banks or in the low terrace areas on the eastern side of the Ōkana Stream, but only 14 species were present in the immediate designated study areas. The additional 21 species planted included 17 taller growing plants, (trees, shrubs, one sedge and climbers) and 4 ground cover species. Of the 21 species, 16 new plant species were introduced into the existing project area. All the plants were monitored over a period of 15 months. The experimental area was a strip of revegetated land approximately 3.5ha (500m long and 70 m wide). Six individual plots (10m x 7m) were located along 70m length of terrace. Each plot measured 70m2 and began at the top of the terrace, with a gentle slope of 0.3m to 1.5 m, down to a low point by the old stream bed. The total width of the study area was 7m for plots on one side, and 7 m wide for plots on the other side of the old stream bed, with a total overall width of the study area of no more than 20m. The experimental plots covered 0.14 ha. A seventh plot was situated at the nearby Wairewa Marae, also measuring 70 m2. A total of 697 plants were included in the field study. Initial strategic planning was found to be important to ensure successful establishment of plants: location and species-suitability issues, as well as known geological, geographical, climatic and biological risks were taken into account at the early stages. Planting techniques, and careful individual plant selection and placement were considered to be important issues. Rare, less common and uncommon plants performed equally as well as the common species. The shade or shelter provided by foliage of the existing plants allowed healthier growth of all species, whereas fringe frost-tender species such as Fuchsia excorticata did not perform as well in the open spaces. One rare species, Pittosporum obcordatum, performed consistently well at all locations. The rate of survival in each species category, was observed in terms of successful establishment, (health and growth), failure, or recovery. Height and health recordings showed that given placement in favourable locations or conditions, such as partial shade or shelter, then the rare, uncommon and culturally useful species could grow equally robustly as the common species. Pseudopanax arboreus had the second highest number of deaths, but was among the tallest growing plants. Three species showed signs of set-backs due to frost damage or summer dryness, followed by new growth and recovery. All Melicytus ramiflorus survived and followed this pattern. When placed in sheltered positions, Pseudopanax arboreus and Fuchsia excorticata, had some success in set-back and recovery. The project resulted in an 87.9% survival rate of the taller plants, and an 82.9% survival rate overall, which included ground cover species. Given the limited period of study and evidence of plant recoveries and set-backs after two winter periods, it was thought that the survival rate maybe improved with further summer data observations. The benefits of a well prepared area in which to allow emergent seedlings to flourish was apparent. Only three emerging seedlings were identified in the unmanaged area compared with several hundred in the managed plots. Many emerging seedlings favoured the protection of the ground-cover species, where these had been placed in cluster groups together. Knowledge gained through this field study has increased biodiversity and Rongoā Māori species in the Te Roto o Wairewa/ Lake Forsyth and Little River areas, informed and raised awareness of the range and opportunities of ecological restoration amongst the Wairewa Rūnanga and local community, and has also advanced restoration practice towards considering how to establish rarer and less common species.