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Methodology
The Originally Rare Ecosystems in the Auckland Region
Thirty three originally rare terrestrial ecosystems, as defined by Landcare Research (Williams et al. 2006), occur in the Auckland Conservancy, excluding the Kermadec Islands.
Ecosystems associated with igneous rocks
The following methods were used to map the originally rare ecosystems associated with igneous rocks:
- Coastal cliffs on silicic bedrock
- Coastal cliffs on silicic-intermediate rock
- Coastal cliffs on mafic rock
- Cliffs, scarps, and tors of silicic rocks
- Cliffs, scarps, and tors of silicic-intermediate rocks
- Cliffs, scarps, and tors of mafic rocks
- Boulderfields of silicic-intermediate rocks
Geology maps (Edbrooke 2002, Searle 1981, New Zealand Geological Survey 1972 and 1982a&b) were used in conjunction with the Land Environments of New Zealand (Leathwick et al. 2002a&b), level three land classes (i.e. levels A1.1, A7.1, D1.1, and D1.2) to determine areas where igneous rocks occur. In instances where the geology map and Land Environments New Zealand (LENZ) had a similar description, rock type and polygon perimeter, the LENZ polygon was copied directly as a GIS data layer. In instances where the geology map and LENZ differed, the rock type and/or polygon was copied from the geology map. In instances where the various geology maps differed, information from the map at the highest resolution was used.
Four igneous rock types occur in the Auckland Conservancy: rhyolite, a silicic rock; dacite, a silicic-intermediate rock; andesite, an intermediate rock; and basalt, a mafic rock (Edbrooke 2002, New Zealand Geological Survey 1972 and 1982a&b). In locations where only one igneous rock type occurred, it was straightforward to determine which rare ecosystem was present. However, in locations such as the Rodney Ecological District and Kawau Island, where more than one igneous rock occurs (e.g. interbedded sandstone with volcanic breccia of andesite and basalt), it is difficult to determine which rare ecosystem is present. In these instances a ‘best guess’ was made and the full geological description is included in the ‘description’ field, should it be necessary to re-classify these areas.
The above rare ecosystems are separated by location (inland or coastal).Active sand dunes
Any polygons classified as duneland in the Auckland Protection Strategy Project were assumed to represent active sand dunes.
Dune deflation hollow
Threatened plant observations from the Department of Conservation BioWeb database and selected records from the Auckland Herbarium were searched for the word ‘hollow’. Observations which were located in a sand dune environment and included this word were classified as a ‘dune deflation hollow’.
Shell barrier beach
Coastlines classified as composed of ‘shell’ in the Coastal Project, and as described by Kenny and Hayward (1996), were assumed to represent shell barrier beaches.
Coastal turf
The following species were chosen as ‘indicators’ of coastal turf: Disphyma australe, Disphyma australe australe, Disphyma australe stricticaule, Gunnera dentata, Selliera radicans, Myosotis pygmaea pygmaea, Ranunculus acaulis, Selliera radicans, Zoysia minima, and Leptinella dispersa rupestris. A location is recorded as having coastal turf if at least one of these species has been observed post-1970. Observations prior to 1970 were included only if it a site visit had taken place to confirm that the species was not extinct at the site. Species observations were obtained from the Department of Conservation BioWeb Threatened Plants database and the Auckland Herbarium.
Stony beach ridges
This ecosystem is defined by rock size as well as presence of a beach ridge. Stony beach ridges identified by Kenny and Hayward (1996) were assumed to represent this ecosystem type.
Shingle beaches
This ecosystem includes rocks which range in size from gravel to cobble. Coastlines classified as ‘pebble’ and ‘cobble’ in the Coastal Project were assumed to represent shingle beaches. The Coastal Project did not cover western coastlines in the Auckland Conservancy, however according to the New Zealand Map Series (NZMS) 260 topographical maps, the western coastline is composed mostly of sand or sand and mud. Shingle beaches are, therefore, unlikely to be present on this coastline.
Coastal rock stacks
Islands digitised from the New Zealand Map Series (NZMS) 260 were classified as a coastal rock stack if they were less than, or equal to, 5.73 hectares in size.
Coastal cliffs on calcareous rocks
Cliffs identified by Kenny and Hayward (1996) as being composed of limestone or exposed coral reefs were assumed to represent this ecosystem type.
Recent lava flows
Recent lava flows were determined as having occurred after 1000 AD. This ecosystem type was identified through descriptions of location and estimated age of volcanoes in the Auckland region as identified by Searle (1981).
Volcanic boulderfields
Polygons classified as volcanic in the Auckland Protection Priorities Project, along with two areas identified on the ground and digitised from aerial imagery, have intact lava-flow vegetation present. These locations were assumed to represent volcanic boulderfields.
Debris flows or lahar
Debris flows of Parnell Grit beds (Kenny and Hayward 1996) and folding/slumping of strata adjacent to Parnell Grit beds (Searle 1981) were assumed to represent this ecosystem type.
Ultramafic hills
Of all the geology maps available, only the New Zealand Land Inventory (New Zealand Geological Survey 1982a&b) was researched at a small enough scale to identify the serpentinite deposits, a component of ultramafic hills, in the Rodney Ecological District. All serpentinite deposits were mapped, regardless of whether they had been quarried or not, because ultramafic vegetation could potentially still be present near the edges of the quarry (PJ de Lange, pers. comm. September 2007).
Cloud forest
Vegetation associations were used to define the location of cloud forest. On Little Barrier Island the Quintinia acutifolia-Ixerba brexiodies-Metrosideros umbellata forest class was used to define cloud forest. On Great Barrier Island the Lepidothamnus intermedius (yellow silver pine) – Agathis austalis (kauri) forest class was used to define cloud forest. Though Quintinia acutifolia is present in the Waitekere Ranges (D Havell, pers. comm. 2007), a suite of cloud forest vegetation is not present because the peaks have a lower elevation and have less than 200 rain days per year.
Hydrothermally altered ground (now cool)
Geothermal springs identified in Houghton et al. (1989) which have ceased discharging were assumed to represent hydrothermally altered ground which is now cool.
Geothermal streamsides
Geothermal springs identified in Houghton et al. (1989) and Wilson et al. (1973) were assumed to represent geothermal streamsides.
Seabird burrowed soil and/or seabird guano deposits
These two ecosystems were grouped together as they are likely to overlap or occur in close proximity in nature. Various methods were used to map these ecosystems.
Polygons were used to delineate the spatial extent of seabird colonies for which locations are fairly well-known (i.e., Muriwai, Rangitoto, central peaks of Great Barrier Island). Experts were also consulted to ascertain which islands in the Auckland Conservancy have, or are likely to have, seabirds present. It was then determined, where possible, the species assemblage and abundance for selected islands. Where seabird locations on an island were not known, the entire island was mapped as a polygon.
Experts consulted include:
- Chris Gaskin, Pterodroma Pelagics NZ
- David Towns, DoC Scientific Officer (Auckland Conservancy Office)
- Matthew Rayner, Auckland University
- Halema Jamieson, DoC Biodiversity Ranger (Great Barrier Area Office)
Cave entrances
Lava cave entrances identified by Kenny and Hayward (1996) were used to map this ecosystem.
Subterranean basalt fields
Surface lava flows depicted in Searle (1981, p54) are assumed to represent the potential locations for subterranean basalt fields.
Ephemeral wetlands
The following species were chosen as ‘indicators’ of ephemeral wetlands: Centipeda minima, Centipeda minima subsp. minima, Epilobium pallidiflorum, Glossostigma elatinoides, Myriophyllum propinquum, Ranunculus amphitrichus, Carex sinclairii, Eleocharis acuta, Isolepis prolifer, Isolepis sepulcralis, Isolepis setacea.
A location was recorded as having an ephemeral wetland if at least one of these species was observed post-1970. Observations prior to 1970 were included only if a site visit had taken place to confirm that the species was not extinct at the site. Species observations were obtained from the Department of Conservation BioWeb Threatened Plants database and the Auckland Herbarium.
The BioWeb Threatened Plants database was also searched for the word ‘ephemeral’ and descriptions which indicated that the wetland water level fluctuated during the year, or was dry and wet during different seasons. Descriptions that met these criteria were used to indicate the presence of an ephemeral wetland.Lake margins
The edges of any polygons classified as lake/open water in the Auckland Protection Priorities GIS Project were assumed to represent lake margins. However, the amount of modification of the lake margins, or whether the lakes are artificial (i.e. man-made) or natural, is unknown.
Gumland
A location was recorded as having gumland if at least one of the following species was identified as being present in the understorey: Schoenus tendo, Gleichenia spp., and/or Baumea spp. and at least one of the following canopy species is present: Leptospermum scoparium, Agathis australis, and/or Phyllocladus trichomanoides. Only permanent PNAP plots from the Waitakere, Rodney, and Hunua Ecological Districts contained species data in enough detail to determine where gumland was located in the Auckland Conservancy.
In locations where several plots of gumland vegetation are clumped together, a polygon was drawn to encompass all of these plots. When a plot of gumland vegetation was located by itself, a 100m radius circle was drawn around the identified point, although though the extent of the gumland vegetation is likely to be much larger. These gumland polygons were clipped to the extent of the existing native vegetation from the Auckland Protection Strategy Project to ensure that polygons identified as gumland only covered areas where native vegetation is known to currently exist.Damp sand plains
The only area in the Auckland Conservancy which was identified as possibly fitting the damp sand plains ecosystem is Whatipu. A polygon of this area was created based on Land Information New Zealand (LINZ) aerial photos.
Dune slacks
Land Information New Zealand (LINZ) aerial photos along with polygons identified in the Auckland Protection Strategy Project were used to map dune slacks. A polygon was classified as a dune slack if it was entirely surrounded by a sand dune, larger than a ‘dune lake’, and was dark in colour – likely indicating the presence of water.
Estuary
Any polygons classified as estuarine/brackish in the Auckland Protection Strategy Project were assumed to represent estuaries.
Seepages and flushes
Observation from the Department of Conservation BioWeb Threatened Plant database and selected records from the Auckland Herbarium were searched for the word ‘seep’, ‘seepage’, and ‘flush’. Observations which included any of these words were classified as a ‘seepages and flushes’.
