An assessment of ecosystem restoration at Styx Mill Conservation Reserve, Christchurch, New Zealand.

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Theses / Dissertations
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Bachelor of Forestry Science
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Walters, Emma

With human arrival in New Zealand, many indigenous flora and fauna have become extinct or endangered. The 90% loss of lowland wetlands, due to conversion and fragmentation, is of significant concern. Large-scale restoration efforts must occur across the country to preserve the remaining ecosystems and re-establish degraded areas. Styx Mill Conservation Reserve (SMCR), Christchurch, New Zealand is a remnant freshwater wetland where restoration activities are occurring. The progress of ecosystem restoration at SMCR will be assessed by understanding how species composition varies across the reserve, determining whether the restoration efforts are creating an ‘ecologically authentic’ representation of the historic ecosystem, and identifying whether, and where, natural seedling regeneration is occurring.

A hierarchical cluster analysis used vascular species composition to identify four vegetation communities at SMCR (low forest, high grassland, riparian/marshland, and low shrubland). An nMDS ordination showed that the low forest community was most distinct from the other communities. The low forest community was abundant in indigenous Griselinia littoralis and Cordyline australis. The other three communities were abundant in exotic Lotus pedunculatus; suggesting that its abundance reduces as forest canopy closes.

Indigenous species that are present in the four О̄tautahi Christchurch Ecosystems Map plant lists (Wet plains – Kahikatea, Dry plains – Tussock, Dry plains – Ti Kouka, and Dry plains – Houhere) were most dominant (mean importance value= 0.22) across the reserve (exotic species= 0.12, indigenous species not present on lists= 0.07). The low forest plots were the only community where the indigenous – present species were significantly greater (p-value= 2.21x10-6) than the indigenous – not present and exotic species.

The species regenerating the most were Coprosma robusta (0.45 seedlings/m2) and Griselinia littoralis (0.42 seedlings/m2). All seedlings were found in the low forest plots, aside from one Coprosma robusta seedling in a riparian/marshland plot.

Restoration at SMCR can be thought of as incomplete, due to the high abundance of exotic species and lack of seedling regeneration in all areas of the reserve apart from the low forest community. The incomplete areas of restoration will require the most attention by management and efforts should be focused on assisting these areas to move to a composition similar to that of the low forest community.

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