Domain C: inland hills and basins

"The earth is what we all have in common."

- Wendell Berry.

 
Map of Domain C: inland hills and basins.
Domain C: inland hills and basins.
See explanation of inset below.
 

Environmental character

Cool, frosty, cloudy and wetter than domains A and B, with a highly seasonal rainfall (winter maximum) and annual mean rainfall of 1168mm. Moderate to steep hillslopes; narrow, steep and winding gullies leading into terraced basins where cool air collects. Complex topography (smooth ridgetops, fault-induced valleys, gullies, river terraces and broad basins) contributes to patchy frosts, turbulent wind flow and variable incident solar radiation.

Generally includes altitude range of 0-400 metres. Mature natural vegetation cover was podocarp/broadleaf forest, with rimu-northern rata penetrating a tawa-dominated canopy.

'Natural' ecological character

Domain C subsections

 
Drawing of Domain C subsections.
Domain C subsections.
 

1. Upper hill-slopes and spurs

Pioneer: manuka (Leptospermum scoparium) scrub.

Secondary: broadleaf scrub and forest dominated by mahoe (Melicytus ramiflorus), karamu (Coprosma robusta), five-finger (Pseudopanax arboreus), rewarewa (Knightia excelsa), tree ferns.

Mature: three-tier podocarp/broadleaf forest dominated by tawa (Beilschmiedia tawa), with rimu (Dacrydium cupressinum) and northern rata (Metrosideros robusta) emergent. Other canopy species may include kohekohe (Dysoxylum spectabile), hinau (Elaeocarpus dentaus), matai (Prumnopitys taxifolia), lancewood/horoeka (Pseudopanax crassifolius), titoki (Alectryon excelsus) and totara (Podocarpus totara) on well drained sites, miro (Podocarpus ferrugineus) increasing with altitude.

Rata viability is low where possum densities are high. Tawa is vulnerable to wind exposure and rodent browse, and will require NZ pigeon/kereru for seed dispersal.

2. Gullies and sheltered foot-slopes

Pioneer: rangiora (Brachyglottis repanda) and manuka (L.scoparium) scrub.

Secondary: broadleaf scrub and forest dominated by rangiora (B.repanda), mahoe (M.ramiflorus), five-finger (P.arboreus), hangehange (Geniostoma rupestre var. ligustrifolium), rewarewa (K.excelsa).

Mature: three-tier podocarp/broadleaf forest dominated by tall pukatea (Laurelia novae-zelandiae), rimu (D.cupressinum), kahikatea (Dacrycarpus dacrydioides) with pigeonwood (Trema orientalis), five-finger (P.arboreus) and tree ferns in non-frosty valleys.

3. Basins and open terraces

Vegetation associations vary according to drainage conditions (from swamps with impeded drainage to excessively drained alluvium), and are frost-tolerant. These areas pool cold air especially at night. Kanuka (Kunzea ericoides) dominates early succession.

4. Shoreline

A low energy, soft shoreline. Streams deposit a gradation of sand to silt at stream mouths and carry suspended sediments during flood events. Zonal associations are created around the shoreline by salt water inundation tolerances of plants and wildlife (saltmarsh, reed and rushland, scrubland of marsh ribbonwood/makamaka (Plagianthus divaricatus) and manuka (L.scoparium), freshwater wetlands of flax, raupo (Typho orientalis) and toetoe (Cortaderia toetoe)). Salt wedges occur up streams and riparian associations here would reflect periodic salt water inundation.

Special features

Fault line running between Pauatahanui and Paekakariki, creating straight-flowing Horokiri Stream.

Continue to Domain D or return to Porirua's Ecological Sites Inventory.