Monitoring and ecology of coastal turf on the Waitakere Coast, Auckland, New Zealand
Biodiversity monitoring is important for both science and environmental management. In the Auckland region, there are established monitoring programmes for forest and freshwater-wetland ecosystems, but currently there is no systematic biodiversity monitoring programme for the terrestrial coastal area. The coastal area includes ecosystems that are often rare, unique and under high development pressures, but the coastal area has less protection than many inland ecosystems. A regional analysis identified nine coastal ecosystems in Auckland, four of which are critically endangered. The rarest of these ecosystems is coastal turf. This thesis uses the coastal turf ecosystem as a case study to assess ecological integrity using measures such as indigenous dominance, species occupancy and environmental representation. Species diversity and abundance were measured at two separate times for three coastal turf locations along the Waitakere coast at Piha, Bryers, and Te Henga (Bethells Beach) using an almost continuous coverage of point intercepts on three subsites within each location. Plants were identified on over 12,000 point intercepts within coastal turf patches ranging in size from 2.8m2 to 164m2. Nineteen native plant species, five exotic species and one exotic species group were identified with native species dominating at two locations, and an approximately equal coverage of native and exotic species found at the third site (Bethells). Repeated sampling of the same subsites was undertaken at time intervals ranging from a few hours to several months to assess short-term sampling error and temporal variation. Natives and exotics were generally found to increase in coverage between sampling events, suggesting a seasonal increase over summer. Patterns in species abundance and composition were mapped in a geographic information system (GIS) and analysed in multivariate ordinations to assess differences in species composition. Changes in bare ground and native and exotic vegetation were graphed as indicators of indigenous dominance and changes related to environmental data on slope, aspect, soil depth and mammal pests were assessed. The species composition of Waitakere coastal turf was similar to previous studies of coastal turf at Great Barrier Island, but different to other locations in New Zealand. Composition was most strongly related to vegetation coverage and to slope. High density, point intercept estimates of cover provided a reliable method to assess status and trends in species abundance and composition at these locations. Although labour intensive, the method provided precise information for these relatively small, rare ecosystems. Recommendations for further research and management include examining long term changes in coastal turfs, their response to threatening processes and investigation of other locations and coastal ecosystem types.