Vegetation assessment of an urban restoration at Styx Mill Conservation Reserve, Christchurch, Aotearoa New Zealand

Human impacts in Aotearoa New Zealand have considerably damaged native ecosystems, and conservation efforts must therefore preserve remaining ecosystems and restore degraded areas. However, restoration efforts must address several challenges including species authenticity, plant survival and seedling regeneration in the presence of exotic competition, browsing mammals, and vagaries of climate. Styx Mill Conservation Reserve (SMCR), Christchurch, contains a remnant freshwater wetland in a floodplain complex where restoration activities were initiated in 2000 under a 40-year plan. This study assesses the restoration progress at SMCR in the face of challenges such as invasive exotic plant competition and defining ecological integrity. Thirty-three vegetation plots were sampled across the reserve and hierarchical cluster analysis was used to define vegetation communities. Species composition of these communities was compared against species lists representing the putative historical plant associations of the Christchurch area to assess ecological integrity of the restoration. Three vegetation communities were identified at SMCR based on vascular species composition: low forest, marshland/low shrubland, and high grassland. The low forest (restoration) community was the most distinct and was the only community in which species regarded as native to SMCR dominated plant diversity and biomass. This community was characterised by planted trees and shrubs. Seedling regeneration of native woody plants including Coprosma robusta, Griselinia littoralis, Pittosporum tenuifolium, and Plagianthus regius was occurring in the low forest plots. Native herbaceous species Carex secta and Phormium tenax were the dominant species across the marshland/low shrubland plots, although taller species such as Cordyline australis occurred in some plots. The high grassland community was dominated by exotic grasses and forbs. Restoration at SMCR is still in the early stages, with abundant exotic plant species present, limited seedling regeneration, and enrichment planting still to be undertaken. The high grassland and marshland/low shrubland sites will require further management attention.