Are cabbage trees worth anything? Relating ecological and human values in the cabbage tree, fl kouka PHILIP SIMPSON piles, and fence posts. The cabbage tree exemplifies the relationship be­ Cabbage trees entered 'New Zealand' along tropical tween people and plants, not only the whole.tree itself archipelagos some 15 million years ago.' They have but also its parts, the leaves, the internal tissues, and adapted to the vicissitudes of sea-level, mountain build­ their biochemistry. ing and erosion, and climate change, and have evolved When Polynesian settlers named the New Zealand into different species and regional forms. A remarkable cabbage trees 'ti' they were retaining a tradition of set of structural and physiological features has devel­ using its tropical relative, Cordyline fruticosa (formerly oped to equip them for survival in a changeable and known as C. terminalis). They brought it with them and sometimes extreme environment. called it tl pore, 'the 'short' cabbage tree. European It was the qualities of strength and durability that whalers and sealers adopted 'cabbage palm' from Cook's were seized on by Maori, and they favoured some or first voyage because the tips of palms were often eaten selected new forms to satisfy their daily needs. The as a vegetable ('cabbage') by sailors, and because of the same qualities of survival underscore Pakeha respect archetypal similarity between cabbage trees and tropi­ for cabbage trees. They too have recognised variety and cal palms that the temperate travellers had seen for the have bred new forms to satisfy their aesthetic mores. A first time. It is perhaps the leafy, tropical look com­ sense of national identity has grown around the cab­ bined with temperate strength that account for the world bage tree and people have been shocked by the epi­ fame of cabbage trees. demic disease 'Sudden Decline'. One of our best known In this paper I am exploring two themes. One is a natural symbols, of strength, uniqueness and humility relationship between natural properties and cultural (someone said 'a real kiwi') has fallen down. What are values. The other, a conservation-driven issue, is the we doing to the world? worth of the cabbage tree. To what extent should we be There are often intimate linkages between the natu­ concerned at the loss of cabbage trees through the dis­ ral values of plants and human uses. For example the ease Sudden Decline? The themes are really one and the totara, an endemic New Zealand conifer, inhabits allu­ same because understanding that a particular value is vial soils where drought and water-logging can occur firmly rooted in an adaptive ecological process (as mani­ repeatedly. The fibrous bark and the tough leaves pro­ fested by particular structural and biochemical features, tect the tree from drought, and the wood is impreg­ for instance), provides a reliable platform for appropri­ n ated with a resin that inhibits damage from water­ ate conservation actions. generated decay. Maori used totara bark for thatching and bird storage baskets, and European settlers fa­ Above: Footrot Flats by Murray Ball helped to encourage voured the wood for those parts of structures that were Government to fund research into the cause of Sudden exposed to rain and the ground: roofing, window sills, Decline, which, however, remains elusive. 14 NEW ZEALAND STUDIES MARCH 1997 BEING A TREE would not survive. Is it a real tree? Foremost among the natural characteristics of the cab­ Each of the thousands of fibres within the trunk of bage tree is its impressive size and longevity. What's so the cabbage tree consists of water- and food-conduct­ valuable about being a tree? 'You can't see the wood for ing cells (xylem and phloem, respectively), the former the trees' means you are preoccupied with detail and wrapped around the latter like reinforcing concrete. cannot see the whole picture or context. Trees grow Now, in a so-called 'real' tree this is not the case; rather, together and form forest (called 'woods' by early Euro­ the xylem forms the woody core of the trunk and the pean explorers, like Bishop Selwyn). phloem forms a cylinder beneath the bark. Such a 'real' Cabbage trees do this by colo­ tree can, therefore, be ring-barked by chopping thro.ugh nising freshly exposed the bark with an axe, which destroys th~ phloem ground (usually wetland and kills the tree. A cabbage tree cannot be formed after a flood, or ring-barked because the water and food­ burnt ground) in dense conducting cells occur together, in stands that last for hun­ fibres, throughout the trunk. This dreds of years. The large is why cabbage trees survive in scale of the resulting paddocks even when stock have forest creates new en­ eaten off the bark to get at vironments that innu­ the tasty food beneath. merable other species of The tasty food is actually organisms can use, the the growth layer (cambium) mutual interrelationships generating diversity and stabil- cabbage tree trunk. The ity. Trees, the largest and old- cambium contains a est organisms on Earth, store of sugar and generate diversity by starch to nourish a creating multi-dimen­ burst of growth in sional habitats in spring when a· new space and sequential crop of leaves is habitats in time. formed. The cambium If there is one single also produces the bark factor that is critical to around the outside of the ability of cabbage the tree, which pro­ trees to actually be tects the softer tissues trees, and is therefore within from physical critical to most of their injury, infection and ecological and cul­ loss of water. The tural roles, it is the growth of wood. Each year the growth layer into a maze of cork­ (cambium) under lined crevices that are the bark produces a ideal for the attach­ new annual ring of wood. Structurally this wood is not ment of mosses and lichens and the fine roots of larger like that of totara or the apple tree, however, prompt­ plants like ferns, lilies and orchids. These epiphytes in ing some people to say, 'The cabbage tree is not a real turn attract a host of animals, so that each cabbage tree tree at all!' The wood is composed of an interconnected becomes an ecosystem in itself. network of fibres, like three-dimensional lace, embed­ ded within packing tissue that stores water and food. Above: Species of Cordyline in New Zealand: The fibrous network conducts food and water between 1. Cordyline fruticosa Pacific Cabbage Tree, n pore the leaves and roots, through the trunk and branches. 2. Cordyline banksii Forest Cabbage Tree, n ngahere The critical property of the network of fibres and the 3. Cordyline pumilio Dwarf Cabbage Tree, n rauriki, mauku turgid packing tissue is the mechanical strength they 4. Cordyline australis Cabbage Tree, n kiJuka provide, which holds up the heavy branches and heads 5. Cordyline indivisa Mountain Cabbage Tree, n TIJ! of leaves, and prevents collapse during storms. Watch From A.L. Poole and N. Adams, Trees and Shrubs of New a cabbage tree in the wind. Without the strength it Zealand (1963). NEW ZEALAND STUDIES MARCH 1997 15 The ability of cabbage trees to produce wood year a tissue that can conduct air, and this allows them to after year for centuries is the fundamental that under­ grow in the waterlogged, oxygen-less soil of wetlands. lies their stature as trees. By being trees, grouped with When they are old, however, they form a very hard others into forests, cabbage trees have the scale and skin that protects the root from damage, especially from complexity to attract and maintain the myriad of other drought. These features of the root explain why cab­ life forms that mutually interrelate. What we commonly bage trees can grow in almost any soil, whether wet or see today however, is a lonely cabbage tree in the pad­ dry, sandy, clay, or rocky, in every climate below about dock, surviving because of its virtues. It has lost its a thousand metres and as part of a wide range of veg­ mates and its future: it is a 'man alone',' against insu­ etation: wetland, shrub land, grassland, duneland or for­ perable odds. est. Cabbage trees are famous for their ability to regen­ But there are other virtues of being a tree. By storing erate and part of the answer lies in the roots. Because a large quantity of water and food, it can survive the roots can form from the cambium on any part of the tough times that inevitably confront a long-lived plant. stem, pieces of branch falling to the ground, even chips The many heads of leaves, over two hundred on a large from the axe, can root and send forth new leaves. tree, make lots of food when times are good. Similarly Leaves the blanket of flowers leads on to a vast crop of fruits In young trees, old leaves die and reflex to form a and seeds. I calculated once, by extrapolating from a 'skirt' that protects the young trunk from damage. Adult sample, that a hectare of trees produces 400 million leaves live for two years so that if one annual set fails seeds. This sort of fecundity is needed by a plant (because of frost, for instance), the other can survive. adapted to the occasional catastrophic flood. By pro­ Leaves are extremely tough: the veins which conduct ducing nutritious fruits in vast numbers, flocks of birds the food and water are covered in long fibres which such as kereru are attracted to disperse them, a fact strengthen the leaf against wind, and the leaf-bases well appreciated by Maori hunters before Queen Victo­ wrap around the stem so that not even a cyclone can ria required the swamp flax for her ships and dairy dislodge them.