Waitakere Ranges – Elements And Interactions, Spatial Variations

Waitakere Ranges – Waitakere Ranges – Elements and InteractionsElements and InteractionsSpatial VariationsSpatial Variations

Element / Interaction Model Element / Interaction Model

GEOLOGICAL / GEOMORPHOLOGICAL

SYSTEMS = RELIEF

PEDOLOGICAL SYSTEM= SOILS

CLIMATICSYSTEM

BIOTIC SYSTEM

= VEGETATION / ANIMALS

ClimateClimate• Climate data shows the Waitakere Ranges are

slightly cooler and rather wetter than the Auckland urban area

Waitakere Ranges:Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rainfall(mm)

140 160 130 175 230 240 260 200 170 190 145 160

Temp( C)

17 17 16 15 13 12 10 11 14 15 16 17

Albert Park in Auckland City:Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rainfall(mm)

75 65 94 105 103 146 142 135 120 102 95 91

Temp( C)

20 20 19 17 14 12 11 12 14 15 17 18

Why?Why?

• Effect of Altitude: roughly 60 temp decrease every 1000m increase in altitude.

Waitakere’s max altitude is just over 400m ►about 30 decrease with altitude

• Exposure to prevailing westerly winds:

Cooling effect of wind

• Orographic Rainfall

Moist air forced to rise

Rain shadow on leeward side

Air warms as it descends

Air cools as it rises

Condensation / Precipitation

Leeward side: Warmer, Drier conditions Windward

side: Cooler, Wetter conditions

Evaporation

• The climate of the Waitakeres is sub-tropical. It lies in the path of prevailing westerly winds which are moist from passing over the Tasman Sea.

• The Block Mountain of the Ranges is prone to predominately westerly winds that are strong. These winds can dry out the western flank (side) of the ranges and cause erosion (aeolian) on the cliffs and ridges.

Relief – Geology / GeomorphologyRelief – Geology / Geomorphology

• Refer back to notes about the formation / evolution of the Ranges

• The Waitakere Ranges are located between Auckland City and the Tasman Sea. It was once a plateau and today rises over 400 metres above sea level. Its features include streams, valleys and gorges and it’s covered in sub-tropical rainforest.

Main landformsMain landforms

• Prominent ridgelines (e.g. Scenic Drive Scarp)

• Incised stream catchments and streams eg Piha Stream

• Elevated hills and plateaus

• Scarps and coastal cliffs

• Peaks

• Wetlands

• Dune systems and sandy beaches

Formation of landformsFormation of landforms

The topography (shape) of a landscape is determined by 2 major processes

• Tectonic processes (mountain building)

• Erosion processes (removal of material from one area to another)

Tectonic ProcessesTectonic Processes

These are caused by movement in the earths crust and cause

• Fold mountains

• Block Mountains eg Waitakeres

• Volcanic mountains – some Waitakere examples eg Lion Rock. Also the whole range is formed from volcanic products ie Manukau Breccia (conglomerate)

Erosional ProcessesErosional ProcessesThese erode (break down) the mountain

landscapes, remove the rock and soil through wind, rain, river and glacial movements. River movements carry the eroded material to lowland areas and deposit it – either on a floodplain (flat lowland area) or in the sea.

• Fluvial – erosion by rivers• Aeolian – erosion by wind• Weathering (chemical, biological and physical)• Erosion / Transportation / Deposition

SoilsSoils

SOIL = the transition zone between rocks and vegetation.

Soils are in a constant state of change and contains:

• Organic matter – decomposed leaf litter, bacteria. Earthworms etc

• Inorganic matter – weathered rock

• Water

• Air

• The soil of the Waitakeres is generally red-yellow podzolic. This is highly fertile and formed from andesitic rocks (that are high in minerals) and has a high clay content. However, soil types vary, depending on where it is located.

• Parent material = Manukau Breccia (volcanic rock – a fragmented andesite)

• Soil type = podzol (reddish-brown in colour)

Reasons / PatternsReasons / Patterns

High rainfall (2000mm per year) AND mild-warm temperatures

= Rapid forest growth

= decomposers (e.g. fungi)

= increased weathering

= fluvial erosion and mass-movement

= poor horizon development

Kauri / Rimu Forest soilsKauri / Rimu Forest soils

• These trees are inefficient at cycling nutrients back to the soil. The litter they drop is acidic and makes the soil infertile

• The litter remains for a long time (slower decomposition) so the soil below is leached

• Grey, structureless topsoil with Yellow – brown podsol subsoil (infertile)

• Silica – rich “pan” (layer) below the topsoil makes drainage difficult (poor for farming)

Other patternsOther patterns

• “Gley” soils = Waterlogged soils around stream floodplains where the soil has a very high water content and is largely anaerobic

• Sandy coastal soils where forest has grown over dunes or sand has blown over existing soil layers

• Thin azonal soils on coastal cliffs / headlands

VegetationVegetation

Vegetation in the Waitakere Ranges is known as “sub-tropical Rainforest”. However, there are variation within the Ranges. There are

• coastal dunes,

• wetlands,

• Variations in sub-tropical forest depending on elevation and flank (west, east, north facing etc).

Forest StratificationForest Stratification

• The forest is made up of several “layers”. The process by which this structure emerges over time is known as stratification– Emergent layer– Canopy– Subcanopy– Shrubs– Epiphytes (grow in the canopy)– Lianas (grow up the tree trunks)– Ground layer (ferns, grasses. mosses etc)

General StructureGeneral Structure

Dominated by Kauri, Rimu and Northern Rata

• The Emergent layer is (or was) the Kauri

• Other Canopy species include:

– Podocarps – Totara, Miro, Kahikatea

– Broadleafs – Tawa, Rewarewa

• Middle canopy (sub-canopy). These include:

– Coprosma species, Mahoe, Ponga - Tree Ferns,

– Nikau Palm, Lancewood,

……continuedcontinued

• Lower shrub and ground level has small ferns, grasses, mosses and lichens.

• Clinging to these species are climbers and epiphytes. These include:

– Climbers - Supplejack, Kiekie, climbing ferns,

– Epiphytes – Kahakaha, Puka

Due to the high rainfall and mild temperatures The Waitakere Ranges contain:

• ¼ of our flowering plants

• 2/3 of our ferns

• 500 developed species

Vegetation PatternsVegetation PatternsVegetation distribution mostly influenced by

micro-climates largely influenced by relief

Ridge Tops…Ridge Tops…Vegetation: • Canopy trees (esp. Kauri and Rata), and lots of

lower canopy trees – manuka, rata and rewarewa.

• Ground cover consists of some ferns, grasses, and hebes.

Soil: • The Humus layer is very thin, as is the A + B

soil horizons. Areas of rock exposed with mosses and ferns

Lower Floodplains…Lower Floodplains…

Vegetation:

• Larger percentage of ferns (ponga’s, grass skirt ponga’s, and nikau palms, some tall canopy trees. It is shadier and the

Soil:

• humus layer is thicker with a more developed soil horizon

Western flank (Tasman coast)Western flank (Tasman coast)Vegetation:

• hardy low lying trees such as manuka / kanuka / cabbage tree / flax / etc – due to strong predominant westerly winds,

• often funnelled through gaps in the sand dunes or up over cliffs / headlands

WildlifeWildlife

• Animals are an important feature living in our native bush. They re-distribute seeds and help the forest to grow and spread. One of the most important birds is Kereru (Native Wood Pigeon). It swallows seeds whole (really big ones too!) and poops them all over the forest. Other species include: Tui, Kaka, Silver Eye, Tomtit etc.