Northern Rata
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''Metrosideros robusta'', commonly known as the northern rātā, is a forest tree endemic to New Zealand. It grows up to or taller, and usually begins its life as a
hemiepiphyte A hemiepiphyte is a plant that spends part of its life cycle as an epiphyte. The seeds of primary hemiepiphytes germinate in the canopy and initially live epiphytically. They send roots downward, and these roots eventually make contact with th ...
high in the branches of a mature forest tree; over centuries the young tree sends descending and girdling roots down and around the trunk of its host, eventually forming a massive, frequently hollow pseudotrunk composed of fused roots. In
disturbed ground In ecology, a disturbance is a change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic element ...
, or where there are gaps in the forest cover, northern rātā will grow on the ground with a normal but short trunk.


Distribution

Northern rātā is found in the
North Island The North Island ( , 'the fish of Māui', historically New Ulster) is one of the two main islands of New Zealand, islands of New Zealand, separated from the larger but less populous South Island by Cook Strait. With an area of , it is the List ...
from Te Paki in the north to
Wellington Wellington is the capital city of New Zealand. It is located at the south-western tip of the North Island, between Cook Strait and the Remutaka Range. Wellington is the third-largest city in New Zealand (second largest in the North Island ...
in the south. Formerly widespread, it is now uncommon over large parts of its former range, and is apparently absent from all but the south-east of
Hawke's Bay Hawke's Bay () is a region on the east coast of New Zealand's North Island. The region is named for Hawke Bay, which was named in honour of Edward Hawke. The region's main centres are the cities of Napier and Hastings, while the more rural ...
. In the
South Island The South Island ( , 'the waters of Pounamu, Greenstone') is the largest of the three major islands of New Zealand by surface area, the others being the smaller but more populous North Island and Stewart Island. It is bordered to the north by ...
, northern rātā is common from
Nelson Nelson may refer to: Arts and entertainment * ''Nelson'' (1918 film), a historical film directed by Maurice Elvey * ''Nelson'' (1926 film), a historical film directed by Walter Summers * ''Nelson'' (opera), an opera by Lennox Berkeley to a lib ...
to
Greymouth Greymouth () (Māori language, Māori: ''Māwhera'') is the largest town in the West Coast, New Zealand, West Coast List of regions in New Zealand, region in the South Island of New Zealand, and the seat of the Grey District Council. The populat ...
and
Hokitika Hokitika is a town in the West Coast region of New Zealand's South Island, south of Greymouth, and close to the mouth of the Hokitika River. It is the seat and largest town in the Westland District. The town's estimated population is as of ...
. It reaches its southern limit near Lake Mahinapua at 42°4′ South latitude. The natural habitat is forest along the coasts and in the lowlands. In some parts of its range northern rātā occurs in montane forest. Formerly, with rimu (''
Dacrydium cupressinum ''Dacrydium cupressinum'', commonly known as rimu, is a species of tree in the family Podocarpaceae. It is a dioecious evergreen conifer, reaching heights of up to , and can have a stout trunk up to in diameter. It is endemic to New Zealand ...
'') it was a dominant tree in a forest type known as rimu/rātā forest. In 2024 an unusual 105 feet (32 meters) tall northern rātā near
Karamea Karamea is a town on the West Coast, New Zealand, West Coast of the South Island of New Zealand. It is the northernmost settlement of any real size on the West Coast, and is located northeast by road from Westport, New Zealand, Westport. Apart ...
on the west coast of South Island, nicknamed the "walking tree" because of its pair of leg-like trunks resembling legs walking across a field, won the
New Zealand Arboricultural Association The New Zealand Arboricultural Association (NZ Arb) is a nationalnon-profit organisationfor arboriculture within New Zealand. The association was formed i1989 representing professional and non-professional people in the arboricultural industry ...
's (NZ Arb)'s Tree of the Year Award with 42% of the public vote.


Description

Northern rātā is a massive tree, easily distinguished from other ''Metrosideros'' species by its small, leathery, dark green leaves that are long, and have a distinct notch at the tip. Young growth is generally pink and covered in fine rust-coloured hairs that are gradually shed as the foliage ages but tend to persist at the midrib and in the vicinity of the leaf base. The flowers, borne in sprays on the tips of branches, are a mass of dark scarlet stamens. Flowering peaks between November and January, and seeds take a year or slightly more to ripen. The bark is usually brown or grey-brown and rather corky and provides an ideal stratum for the roots of epiphytic plants such as ''
Astelia ''Astelia'' is a genus of flowering plants in the recently named family Asteliaceae. They are rhizomatous tufted perennial plant, perennials native to various islands in the Pacific, Indian, and South Atlantic Oceans, as well as to Australia an ...
'' species and ''
Freycinetia banksii ''Freycinetia banksii'', also known as kiekie, is a densely branched, brittle, woody climber native to New Zealand. It is a member of the screwpalm family Pandanaceae. Description ''Freycinetia banksii'' is a densely branched woody climber, w ...
'' (kiekie). The wood is reddish brown, and the manner of its growth results in a twisted grain.


Hemi-epiphytic growth habit

Northern rātā often begins life as hemi-epiphyte, and the resultant tree has a hollow trunk up to 4 m in diameter made up of interlocking roots that enclose the space left by the former host tree. The host tree of epiphytic northern rātā is usually
rimu ''Dacrydium cupressinum'', commonly known as rimu, is a species of tree in the family Podocarpaceae. It is a dioecious evergreen conifer, reaching heights of up to , and can have a stout trunk (botany), trunk up to in diameter. It is endemis ...
. In former times, the tree was described as a 'strangler', however it may be that rātā can only establish in trees that are already in decline. Northern rātā usually occurs in hardwood, podocarp, and
southern beech ''Nothofagus'', also known as the southern beeches, is a genus of 43 species of trees and shrubs native to the Southern Hemisphere, found across southern South America (Chile, Argentina) and east and southeast Australia, New Zealand, New Guin ...
forests. It is often associated with such species as rewarewa, tawa, hīnau,
kānuka ''Kunzea ericoides'', commonly known as kānuka or white tea-tree, is a tree or shrub in the myrtle Family (biology), family, Myrtaceae and is endemic to New Zealand. It has white or pink flowers similar to those of ''Leptospermum'' and from its ...
,
kahikatea ''Dacrycarpus dacrydioides'', commonly known as kahikatea (from Māori language, Māori) and white pine, is a Pinophyta, coniferous tree endemism, endemic to New Zealand. A Podocarpaceae, podocarp, it is New Zealand's tallest tree, gaining hei ...
,
kāmahi ''Pterophylla racemosa'', commonly known as the kāmahi, is an evergreen tree endemic to New Zealand. It is a member of the Cunoniaceae family of plants, and it is often referred to by its former botanical name ''Weinmannia racemosa.'' Most me ...
,
kohekohe Kohekohe (''Didymocheton spectabilis'') is a medium-sized tree in the Meliaceae family, native to New Zealand. It is found in lowland and coastal forests throughout most of the North Island and also occurs in the Marlborough Sounds in the no ...
, pukatea and māhoe.


Conservation

The greatest threat to northern rata is browsing by introduced possums (''Trichosurus vulpecula''), which cause severe damage by eating the leaves, buds, flowers and young shoots of the tree. In severe cases this can lead to the death of the tree within two years. In some districts, this has resulted in the local loss of the species. The situation of the species has been improved through the efforts of
Project Crimson __NOTOC__ Project Crimson is a conservation initiative to promote the protection of the pōhutukawa and the rātā which are under threat due to browsing by the introduced common brushtail possum. The vision of the project is to "enable pōhutu ...
. Hybridisation with
pōhutukawa Pōhutukawa (''Metrosideros excelsa''), also known as the New Zealand Christmas tree, or iron tree, is a coastal evergreen tree in the Myrtus, myrtle family, Myrtaceae, that produces a brilliant display of red (or occasionally orange, yellow o ...
is another threat to the survival of northern rātā. Pōhutukawa has naturalised in areas south of its natural range, and poses a problem in localities where the northern or southern rātā species are present. Other threats include cutting for firewood, and forest clearance for roading or construction.


Cultivation

Northern rātā may be propagated readily from fresh seed. Viability of the seed drops quickly after a few weeks or if it is allowed to dry out. Cuttings do not strike readily, but better results can be obtained from using water shoots. At least three
cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...
s of northern rātā have been released. There are also known cultivars of hybrids between northern rātā and pōhutukawa (known as ''Metrosideros ×sub-tomentosa''), and between northern rātā and southern rātā. Known cultivars include: ∞ Hybrid of northern rātā and southern rātā
¤ Hybrid of northern rātā and pōhutukawa


See also

*''
Metrosideros excelsa ''Metrosideros'' is a genus of approximately 60 trees, shrubs, and vines in the family Myrtaceae, mostly found in the Pacific region. Most of the tree forms are small, but some are exceptionally large, the New Zealand species in particular. The ...
'', pōhutukawa *''
Metrosideros umbellata ''Metrosideros umbellata'', the southern rātā, is a tree endemic to New Zealand. It grows up to or more tall with a trunk up to or more in diameter. It produces masses of red flowers in summer. Unlike its relative, northern rātā, this sp ...
'', southern rātā *'' Metrosideros bartlettii'', Bartlett's rātā *'' Metrosideros parkinsonii'', Parkinson's rātā


References

*Salmon, J.T., 1986. ''The Native Trees of New Zealand''. Wellington: Heinneman Reed. *Simpson, P., 2005. ''Pōhutukawa & Rātā: New Zealand's Iron-Hearted Trees''. Wellington: Te Papa Press. * * * * * {{Taxonbar, from=Q744244
robusta ROBUSTA (Radiation on Bipolar for University Satellite Test Application) is a nano-satellite scientific experiment developed by the University of Montpellier students as part of a Centre National d'Études Spatiales (CNES) call for student proje ...
Endemic flora of New Zealand Trees of New Zealand Epiphytes