The following is an article by Neil Faullknor, Land Management Officer, about the evolution and history of native vegetation in New Zealand and Hawke’s Bay.
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New Zealand’s indigenous vegetation is unique, evolving in virtual isolation for some 80 million years, the assigned date for the drifting of the New Zealand area from the super continent, Gondwanaland. Recent work by the Institute of Geological and Nuclear Sciences, presented by Dr Hamish Campbell, suggests that the New Zealand continent, or Zealandia, moved away from NE Queensland. This work suggests that all New Zealand rocks evolved from greywacke, and the only source of suitable greywacke is NE Queensland. This continent of Zealandia, including undersea parts, was about half the size of Australia, and carried with it plants and animals, including dinosaurs.
Small fossils of around 10 different dinosaurs have been found, and it was also suggested that though New Zealand is bereft of mammals, with native bats minor exceptions, other mammals could have been present, as mammals evolved at the same time as the dinosaurs. It was also suggested that 25 million years ago, most, if not all of Zealandia submerged, suggesting that the present plants and animals may not have originated from Gondwanaland, but evolved in the 25 million years since re-emergence.
Earlier work (Fleming 1979, Stevens 1974 & 1980, Gage 1980, and Cumberland 1981), quoted by Newsome (The Vegetative Cover of New Zealand, 1987), traced the origins and links of New Zealand flora and fauna.
Though theories and hypothesises have been presented about the original continents of Ur, Artica and Atlantica, and the events and break ups that occurred, resulting in other super continents including Gondwanaland, the events relating to the New Zealand area, date from around 300 my ago, and the deposition of sediments in the NZ geosyncline.
Beginning 150 my ago and continuing for some 50 my, the Rangitata orogeny caused ancestral NZ to emerge, extending from New Caledonia in the north to Campbell Island in the south. With a climate considered to be similar to today, plants and animals evolved/colonised including leiopelmid frogs, tuatara, ratite birds, and podocarps, kauri and ferns.
Another significant period was the drifting of NZ from Gondwanaland (NE Queensland coast), some 85 to 80 my ago. Ancestors of the southern beeches are considered to have appeared about this time.
From 80 to 60 my ago drifting of the continents continued as did plant distribution. Ancestors of tawa and rewarewa are recognised from this period, but it is considered that competition and climatic fluctuations may also have led to extinctions of some species.
This earlier work also considers submergence of much of the land area, and peneplanation of the remainder during the period 60 to 15 my ago, with climatic fluctuations from warm temperate to cold temperate, and two pronounced warmings to sub tropical 55 my ago and 15 my ago. The Antarctic ice cap has been dated as 45 my old.
New Zealand flora was evolving separately now from previously closely (?) related South American, Australian, New Guinean, and Antartican. Podocarps are considered to have been dominant, but also recognisable were the ancestor of fushia, hinau, kamahi, kohekohe, puketea, rewarewa, rata, tawa, coprosma spp, leptospemum spp, pittosporums, and ferns, epiphytes grasses and lianas.
Fleming noted three geographic affinities in these species –
- Australia – leptospermum
- Paleo austral – beeches, podocarps, and rewarewa
- Malayo Pacific – ferns, nikau, kohekohe, tawa and mangroves.
The last major geologic events affecting the New Zealand region is considered to be the Kaikoura orogeny, some 13 my ago, with the uplifting of the current land mass of NZ.
From this period, the major influence on NZ’s evolving flora and fauna would have been the climate, beginning with the Pleistocene glaciation, 2 my ago. From this period to some 10,000 years ago, an increasingly severe climate, saw the retreat of forest species north and to lower altitudes. Into the vacant habitats moved shrubs and grasses that were able to tolerate the conditions. The zone between permanent ice and snow and the lower tree line, is considered to have been filled by speciation and hybridisation of lowland and montane genera, i.e. celemisia, coprosma, dracophylum, hebe, myrsine, and podocarps. Other species may have arrived by migration, including epilobium, gentiana, and ranunculus. Extinction of species also occurred i.e. the large leafed beeches, which are still common in New Guinea and New Caledonia. Complete vegetation recovery is considered to have occurred in the interglacial periods so that forest covered all but the most arid lowlands, and extended up mountain slopes to high shrublands, grasslands and alpine herb fields.
Gradual warming occurred till about 8000 years ago, the end of the glacial period, or the beginning of the post glacial period, with only minor climatic fluctuation since that time. These would have only resulted in small adjustments in plant distribution. It is generally considered that spectacular but localised changes resulted from natural fires, and volcanic events, though there is some debate on the actual effect of the volcanic eruptions.
From this period on, the greatest and most negative influence on the flora and fauna of New Zealand has been from humans. The arrival of Polynesian peoples is considered to have occurred around 750 to 800 AD. These canoes would have carried tropical foods such as kumara, taro, yams and gourds and it is deduced that to cultivate these plants, early settlement would have been concentrated in the north of the country. These early colonisers brought and used fire, perhaps one of the greatest influences on NZ flora. The firestick is well documented as an important part of a travelling kit, used to clear travel ways through New Zealand’s dense natural forest. Abel Tasman noted extensive fires on the west coast of the South Island some 250 years ago.
The effect of fire varied from region to region. It is safe to assume that the heavy forest and moist climate of the north would not be conducive to fire spread, as were the central, eastern and southern regions. It is recorded that fire was used to prepare transport routes, flush moa, and prepare ground for bracken growth.
New Zealand’s climate and topography also had and influence on the effect of, and recovery from fires. With a predominantly westerly airflow, and interception of rainfall by the central mountain chains of both islands, the eastern regions are in a rain shadow and thus grew less dense podocarp/broadleaf and beech forests, that were less able to recover from repeated burning. It is considered that forest was eliminated from much of the eastern lowlands from northern Hawke’s Bay to Southland, during this period. Figures quoted are a forest cover of 75% in 700 AD, reducing to 55% in 1800 AD.
The next major influence was the arrival of Europeans. Early arrivals, people like whalers, sealers, and others, brought the first truly exotic plants, including the potato. A new era of forest clearing occurred to allow the cultivation of these new crops for consumption and trade.
An interesting quote, earlier referred to in reference to the effect of volcanic eruptions on forest clearance, was an account in 1843 by Dieffenbach (reproduced in 1964 by Cameron).
“It is evident that the forest has at some former period covered a greater extent of the land in the neighbourhood of Taupo than it does now: it does not appear to have been destroyed by volcanic eruptions, but by the fires kindled by the natives in order to clear the ground for the purposes of cultivation.”
The next, and perhaps greatest influence, certainly the most organised and systematic, was the clearance of the forest by European settlers for the establishment of English grass pastures.
“Increasing European settlement heralded the most far reaching and rapid changes in New Zealand’s long history.”
Often sawmills were established to cut timber from fallen logs, but in many inaccessible or remote areas, the forests were just cut and burnt. Post WW1 saw another period of intensification of land clearance, with the subdivision of many larger properties for the provision of rehab settlement farms for returning servicemen, and the development of poorer pasture and scrubland.
By the middle 1900’s virtually all the plains and downlands and much of the low hill country had been cleared of forest and converted to agricultural use.
The other significant influence on native flora and fauna, in conjunction with human activities noted, was the introduction of exotic plants and animals.
Mapping of the current vegetative cover of New Zealand, as carried out by Newsome in 1987, gives some indication of what the original vegetation may have been. From small remnants in inaccessible areas, maybe with what are assumed to be climax species, assumptions are made that these are representative of the original cover, despite the fact that all such areas have been modified to some extent.
Evidence of tree remains, stumps, and charcoal, suggest that the eastern HB was extensively forested by broadleaf and podocarp species. The species listed in the DOC, PNA report, and all which have been noted, are –
On mudstone faces and in the gullies, species including -
- Tawa – Beilschmiedia tawa
- Titoki – Alectryon excelsus
- Rewarewa – Knightia excelsa
- Lacebark – Hoheria populnea
- Ti Kouka (Te Rakau) – Cordyline australis
- Kanuka – Kunzea ericoides
- Kaikomako – Pennantia corymbosa
- Pigeonwood – Hedycarya arborea
- Hinau – Elaeocarpus dentatus
- Mahoe – Melicytus ramiflorus
- Lancewood – Pseudopanax crassifolius
- Lemonwood (Tarata) – Pittosporum eugenoides
- Kahikatea – Dacrycarpus dacrydioides
- Totara – Podocarpus totara
On alluvial terraces, the podocarps,
- Kahikatea – Dacrycarpus dacrydioides
- Totara – Podocarpus totara
- Matai – Prumnopitys taxifolia
with broadleafs such as,
- Titoki – Alectryon excelsus
- Black maire – Nestegis cunninghamii
- White Maire – Nestegis lanceolata
- Narrow leafed maire – Nestegis montana
- Ti kouka – Cordyline australis
- Lacebark – Hoheria populnea
- Ribbonwood – Plagianthus regius
- Kowhai – Sophora tetraptera (some S. microphylla in southern part of district).
Many small leafed understory species occur through these remnants. Pittosporum obcordatum (heart leafed kohuhu) is noted as a vulnerable specie.
Nearer the coast other species occur such as,
- Ngaio – Myoporum laetum
- Karaka – Corynocarpus laevigatus
- Pukatea – Laurelia novae-zelandiae
- Nikau – Rhopalostylis sapida
- Titoki – Alectryon excelsus
- Mahoe – Melicytus ramiflorus
- Lacebark – Hoheria populnea
- Putaputaweta – Carpodetus serratus
- Wharangi – Melicope ternata
In the south of the area, near Porangahau, on harder argillite hill country, remnants of beech forest, principally black beech, Nothofagus solandri, remain.
The coastal margin of much of the area consists of steep unstable faces. Few beaches are present and the steep slopes rise up from wave cut platforms. These steep faces probably never supported tall forest and the current vegetation of:
- Wharariki – Phormium cookianum
- Tauhinu – Cassinia leptophylla
- Manuka – Leptospermum scoparium
- Kanuka – Kunzea ericoides
probably reflects the original vegetation.
The most extensive beach area is at Porangahau (Te Paerahi), where native sand plants such as pingao and spinifex are rare and threatened by the introduced marram grass.