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In The Hills In The Hills 2015-03

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This article was first published in the Tararua Tramper Volume 87, no 2, March 2015

March in the hills with Chris Horne and Barbara Mitcalfe

Dacrycarpus dacrydioides, kahikatea, white pine

At least 60 m - 65 m in height, kahikatea is believed to be our tallest tree species. With a lifetime estimated to be 600 1000 years, it is also one of our longest-lived. A NZ endemic, kahikatea is found throughout the country, including Rakiura/Stewart Island. It favours moist sites up to 600 m elevation, including swamps, fertile flood plains and river terraces. Locally you can see fine examples in the water catchment area in Wainuiomatā Valley.

During their long lifetime, kahikatea adopt a series of distinctive, characteristic shapes. Beginning in Stage 1, as straggly seedlings, these spindly young trees take many decades to reach Stage 2, which is an easily-recognisable conical form, tapering to a point at the top, like a Xmas tree. Hundreds of years later, these will have reached Stage 3, i.e., maturity, having gained much height and become columnar, with a tall, very slender crown. Finally, in Stage 4, the crown of the aging tree broadens dramatically and opens out into a rounded shape.

Kahikatea trunks can exceed 2.5 m in diameter. Older trunks are usually vertically fluted, and buttressed at the base. The grey bark often peels off in oval flakes, giving the trunk a 'hammer-marked' appearance. The young leaves are soft to touch and measure c. 7 mm x 2 mm. The scale-like, mature leaves are c. 2 mm x 1 mm.

Kahikatea.jpg: 1030x690, 82k (2016 Oct 25 23:20)
A luscious kahikatea receptacle, topped by a ripening seed.
Photo: JEREMY ROLFE

Like all our NZ conifers (see February Tramper), kahikatea are usually dioecious. The male trees produce pollen 'cones', and the female trees produce seed 'cones'. Both types of cones are only c. 1 cm long and are found at the end of slender branchlets. The male cones are covered in scales which tightly overlap each other until, at pollination time, they are forced apart by the developing pollen underneath them, and millions of minute pollen grains escape into the air, to be carried away by the wind, to try their luck!

Meanwhile in another part of the forest, so to speak, millions of tiny female cones are developing and ripening. Each of them perches on the swollen, juicy tip of its twig, which is called a receptacle - see image. Each cone has a minute aperture, and guess what? At least one wind-driven pollen grain will enter the aperture and begin the process of fertilisation of the ovule, which usually takes several months.

The receptacles are often mistaken for fruit, because as they mature they turn red, attracting kererū, tūī and kākā, which gobble them up together with the ripened, black seeds. Entire female kahikatea trees can appear orange-red in autumn when this phenomenon advertises that the time has come for birds to plunder the bounty and thus propagate the species, a mutually-useful arrangement.

Use

The juicy receptacles were also an important food for Māori - sweet, with a slightly piney aftertaste. One feast was recorded as serving 60 baskets of it. They also made a tonic by steeping chips of the wood in boiling water, then drinking the liquid. Kahikatea wood was their favourite for making bird spears, and the soot derived from burning the heartwood was used as a tattooing pigment.

From 1885 to the 1940s, the main use of the wood was in making parchment-lined butter boxes to hold 56-pound slabs for export. Kahikatea wood was ideal for this use because it is odourless, clean-looking and lightweight. This usage, together with concrete boxing for the Clyde Dam, led to the destruction of extensive stands of kahikatea. Because a towering kahikatea is a whole ecological community supporting 'nests' of epiphytic fern, orchid, shrub, liane, lichen, moss and sedge species, not to mention hundreds of vertebrate and invertebrate animal species, one can easily imagine the huge amount of indigenous biodiversity that was lost with the trees.

Category
Botany 2015

Page last modified on 2017 May 27 04:13

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