Journal archives for July 2022

31 July, 2022

Vegetation of the Port Hills, Christchurch: Shrublands

The Port hills are a hill range directly South of Christchurch city, Canterbury. They are approximately 25 kilometers in length and reach a height of 573 metres at Coopers Knob / Omawete. As a geographical feature of Christchurch, the hills are greatly valuable as they provide a wide variety of recreational activities and an iconic backdrop to the city. (They also provide useful reference points when trying to navigate some of the deep dark suburbs of Christchurch...)

The vegetation of the hills vary considerably, and provide the foundation for the biodiversity and economy of the region. The hills are a mix of suburbs, grazing paddocks, tussock grasslands, exotic scrub, rock outcrops, forestry blocks, native scrub and indigenous forest. The hills form one side of the Lyttelton crater, the remains of an ancient volcano which now exists as a harbour. Because of this geography, the hill slopes facing the harbour side are steep, whereas the slopes facing away are relatively gradual. The hills can also be divided another way: north and south, with the border between the two regions situated approximately at Dyers pass. The differences between both regions are in altitude, with the lower north side reaching a max height of 499m at Mt. Pleasant. Characteristics of the north side also include a peninsula-like geography, with the hills somewhat isolated between Pegasus bay and Lyttelton harbour, with the settlements of Lyttelton and Sumner on either side. The north side is also more urbanised, with the much larger south side being fairly rural, private and not as popular with recreationalists. The altitude of both regions effects weather somewhat, rain is generally less frequent on the north side, and the south side is wetter. However, there are exceptions with both regions with wet and dry areas occurring in both.

Native scrub

Native scrub is found throughout the hills, especially on south side slopes and gullies with regenerating bush. Native scrub also occurs in small stands on rocky bluffs. Much of the species are small-leaved and divaricating species, but also larger leaf species as they develop into trees.

Native scrub has a biodiversity significance similar to native forests, with a high diversity of native trees giving habitat to native birds and insects.
Shrub species found in native scrub include (39 species, 3 hybrids):
kānuka (Kunzea robusta)
kaikōmako (Pennantia corymbosa) - juvenile form - somewhat divaricating
horopito (Pseudowintera colorata) - becomes large tree
matipou (Myrsine australis) - becomes large tree
kōhūhū (Pittosporum tenuifolium) - rocky outcrops, becomes large tree
akiraho (Olearia paniculata)
pāpāuma (Griselinia littoralis) - becomes large tree
horoeka (Pseudopanax crassifolius) - becomes tree
rōhutu (Lophomyrtus obcordata) - becomes tree
tūrepo (Streblus heterophyllus) - becomes tree
fragrant tree-daisy (Olearia fragrantissima) - divaricating, rare
yellow wood (Coprosma linariifolia) - divaricating, becomes tree
thick-leaved miki (Coprosma crassifolia) - divaricating, drier regions
grey miki (Coprosma dumosa) - divaricating, higher altitude, south
blood wood (Coprosma wallii) - divaricating, uncommon
black miki (Coprosma propinqua) - divaricating
small-leaved karamū (Coprosma x cunninghamii)
rigid miki (Coprosma rigida) - divaricating
Coprosma rubra - divaricating, uncommon
Coprosma virescens - divaricating, uncommon
karamū (Coprosma robusta)
shiny karamū (Coprosma lucida) - wet areas and outcrops
Porcupine shrub (Melicytus alpinus) - divaricating, dry areas
niniao (Helichrysum lanceolatum) - wet areas
korokio (Corokia cotoneaster) - divaricating, dry areas
tarangahape (Carmichaelia australis) - dry areas, can form distinctive stands
poataniwha (Melicope simplex) - divaricating
Raukaua anomalus - divaricating
koromiko (Veronica salicifolia)
Banks Peninsula hebe (Veronica strictissima) - rocky outcrops, endemic to region
tūmatakuru (Discaria toumatou) - dry areas, divaricating
weeping māpou (Myrsine divaricata) - divaricating
(Fuchsia x colensoi) hybrid
tāwiniwini (Gaultheria antipoda) - rare, high altitude
poroporo (Solanum laciniatum) - also found in disturbed and suburban zone
tororaro (Muehlenbeckia complexa) - climber which forms dense shrubs - often a component of drier shrubland communities
mingimingi (Leucopogon fasciculatus) - uncommon
Mountain pinkberry (Leptecophylla juniperina) - dry areas
inaka (Dracophyllum acerosum) - rare, high altitude
Olearia x macrodonta - ?
mountain akeake (Olearia avicenniifolia)
prostrate kowhai (Sophora prostrata) - dry areas, divaricating

Divaricating plants, for those not familiar:

Native scrub/shrubland communities

Native scrub differs depending on which part of the hills an observer is situated. Typically, shrubland on the North-east of the hills is a mosaic of shrubs within grass or tussockland. It is characterised by particular species which favour the lower, drier environment. These communities include tororaro (Muehlenbeckia complexa), black miki (Coprosma propinqua), thick-leaved miki (Coprosma crassifolia), kānuka (Kunzea robusta), Porcupine shrub (Melicytus alpinus), tūmatakuru (Toumatou discaria), small-leaved karamū (Coprosma x cunninghamii), korokio (Corokia cotoneaster) and Prostrate kowhai (Sophora prostrata). These shrubland "mosaics" are habitats for native and introduced bird species, insects and spiders. They are also characteristic of the "dryland" Port Hill ecological landscape. These shrublands are generally easy to navigate through.

On the wetter and often darker South-east and west of the hills display a different type of dense shrubland, something I would call "pre-forest shrubland". This is characterised by dense stands of native (and often
exotic) shrubs standing 1-2 metres tall. These shrublands often cloak hill gullies and seemingly random hillsides. They are often regenerating indigenous forest, and increase in ecological value with age. They provide habitat and food sources to a variety of bird and lizard species, and are important due to their significant role in sucking carbon dioxide out of the atmosphere. Species of these communities include natives such as mahoe (Melicytus ramiflorus), kānuka (Kunzea robusta), pāpāuma (Griselinia littoralis), kōhuhu (Pittosporum tenuifolium), Mangrove-leaved daisy-bush (Olearia avicenniifolia), shiny karamū (Coprosma lucida), yellow wood (Coprosma linariifolia), blood wood (Coprosma wallii), Coprosma virescens and exotic shrubs such as Scotch broom (Cytisus scoparius), Gorse (Ulex europaeus) and Himalayan honeysuckle (Leycesteria formosa). Many more species can be spotted among these shrublands, making them always interesting to study.

Those who see the Port Hills as basic grasslands with little variation are mistaken, although understandably. When looking a little more closely, we can see a vast variety of species in the mosaic of shrublands alone, which are essentially 'in-development' indigenous forest, and still host fauna species and a variety of ground ferns and herbs. The vegetation cover of the Port Hills additionally contributes to climate change reversal, in a small way. There is definitely a problem of exotic weed-dominated shrublands on the Port hills, with a few particular culprit species doing the most harm. However, these species are often nitrogen fixers, providing nutrients to the soil and even providing sustenance to native fauna (kererū, Hemiphaga novaeseelandiae, consume broom flowers, and many pollinators find the vast amount of weed flowers useful). I would suggest the seeding of native species underneath exotic shrublands which have reached a maximum height, as these weeds have been shown to assist native seedlings in establishing more valuable native shrubland on other parts of Banks Peninsula (Hinewai Reserve).

Above: A large Prostrate kowhai (Sophora prostrata) shrub on the dry North-east Port hills area. 380m above sea level.

Above: A community of shrubland plants in the Southern Port hills. 460m above sea level.

Posted on 31 July, 2022 01:31 by noahfenwick noahfenwick | 0 comments | Leave a comment