The Secret Life of Trees
Page 5
In temperate forest you can be fairly sure that any one tree is the same species as the one next to it – or at least, it will be one of a cast list that is unlikely to exceed more than half a dozen (oak with ash in much of Britain; lodgepole pine with aspen in much of Canada; alder, Scots pine and spruce in the Baltic; and so on). But in Amazonia in particular you can be fairly sure that any one tree is not the same species as the one next to it. Often there is half a kilometre between any two trees of the same species and there can be up to 300 different species of tree in any one hectare. So the task, often, is to identify an individual tree that may be not much thicker than your arm from the appearance of its bark, out of a total cast of several hundred (or thousand) possibilities – which may well include some that haven’t previously been described, so that there is nothing to refer back to.
In practice, there are three main routes to identification, whether of trees or of any living creature, and in practice botanists and foresters use them all together. The first is to make use of botanical ‘keys’. These are lists of characteristic features with a series of decision points, which you work through like a flow chart, as in: ‘Do the flowers of this particular plant have four petals, or five?’ If four, you move to question X, and go on from there; if five, you go on to Y, and so on. Such keys first became popular in the eighteenth century. The great French biologist Jean-Baptiste Lamarck, best remembered for his pre-Darwinian theory of evolution, was particularly good at devising them. They are very much in the spirit of the Enlightenment.
The second, ultra-modern way to identify a tree – or any living creature – is to sample its DNA. Modern scientists working in tropical forest commonly take a bore of cells (a biopsy) from the cambium under the bark, which is the most reliably accessible living tissue in a tree. They then send the sample back to the laboratory (although field tests of DNA are becoming available).
Ultimately, both of these standard methods – the diagnostic keys, and the DNA printouts – rely on some kind of central reference point of information. The principal kind of reference point in botany is the herbarium, a central collection of plants kept in dried and mounted form (though some bits might be pickled, and there might be microscopic slides, and so on). There are many herbaria worldwide, each specializing to various degrees. Some, like that of the Royal Botanic Gardens, Kew, are extremely wide-ranging. Others focus on the particular plants of a particular region. Scattered among the various herbaria are the ‘type specimens’: the first examples of the species ever to be formally described.
But there is a third way to identify plants – and this is simply to know. This is how we recognize friends and family. Recognition is unconscious; and the unconscious does not need to check out the shortlist of diagnostic features that the key-maker or the forensic image-makers must refer to, but takes into account a dozen (or a hundred?) secondary cues – quirks of speech, expression, and so on. Many people grew up in tropical forests and some of them recognize trees from the feel of their leaves, their scent, or indeed the texture of their bark, as readily as any of us recognize our cousins and our aunts. In Brazil these indigenous experts are called mateiros. Mike Hopkins of EMBRAPA (Brazil’s research centre for forestry and agriculture) told me that he has sometimes known mateiros disagree with specialist botanists. Typically, the botanist says that two similar trees are the same, while the mateiro says they are different. Resolution becomes possible when DNA from the cambium is analysed, or the trees bear flowers and fruit. In such disputes, says Dr Hopkins, ‘I have never known the mateiros to be wrong.’
The mateiros are wonderful but they have their limitations. A mateiro who is supremely at home in one place, may be less at ease in another, which may well have a different complement of trees. Then again, the subtleties of the subconscious are not easily conveyed. It’s important that everyone who visits the forest with a serious purpose – scientist, environmentalist, forester – should be able to identify what they see. To convey the information formally and reliably, we have to go back to basic diagnostic features that can easily be described: whether the leaves are alternate or opposite, the texture of the bark, and so on. In short, identification needs formal field guides and/or keys, and herbaria in scholarly centres where difficult material can be assessed definitively, and preferably a lab for molecular biology – and the mateiros. Sometimes all are available. Sometimes not.
To see how hard life can be for botanists in tropical forest we have only to look at the wondrous Reserva Florestal Adolfo Ducke (which rhymes roughly with ‘booker’): a hundred square kilometres (roughly 10 x 10 km) of pristine forest in northern Brazil, about a thousand miles up the Amazon river, just outside Manaus. The Ducke Reserve has been studied intensively for decades. Sir Ghillean Prance, formerly director of the Royal Botanic Gardens, Kew, has been working there on and off since 1965. When he first arrived the total species list of ferns and flowering plants that had by then been identified stood at a little over 1,000, of which about 60 per cent were trees. He and the other resident and visiting botanists steadily added to the species list and by 1993 it ran to 1,200. A high proportion of their additions were orchids.
The botanists aimed from the outset to produce a key to the native plants but, says Professor Prance, ‘all of us got diverted’, and they never got around to it. But at last, in the early 1990s, helped by the National Research Institute of the Amazon (INPA) and a grant from the British government, botanists were recruited specifically to provide the much-needed flora and guide. Mike Hopkins was appointed as one of the two coordinators. In truth he was not a botanist but an insect specialist (an entomologist) from Wales (via Oxford). But he pointed out to the appointments board that the guide was intended to be read and used by all who were interested – and if it was prepared by botanists, then, he argued, only botanists would be able to follow it. ‘But if I can understand it,’ he said, ‘then anybody can.’ Ghillean Prance supported his case and Hopkins got the job. A succession of Brazilian scientists have also acted as coordinators.
It took five years of focused study to produce the guide – and that five years more than doubled the species list that first confronted Ghillean Prance in the mid 1960s. The total inventory now stands at 2,200, of which about 1,300 are trees. Not all of the additions are new to science, of course. But some of them are (including more orchids). From all this, three points are abundantly clear. First, identification really can be difficult – for it had taken decades to produce the species list of 1965 that included only half the species in the Ducke Reserve. Secondly, in the tropics at least, the more that botanists look, the more they find. Thirdly, the tropics really are extraordinarily diverse. The Ducke Reserve is about two thousand times smaller than Britain (which has 2.3 million square kilometres), but it has forty times as many native trees.
Anyway, in 1999 the team that Dr Hopkins coordinated finally produced the Flora da Reserva Ducke, a magnificent work that drips with colour photographs and diagrams of everything pertinent, and allows identification not simply from the flowers and fruits that are commonly taken to be definitive but are usually absent, but also from the leaves, twigs and all-important bark. The guide would be among my favourite reading, if only it wasn’t in Portuguese.
Practical, hard-headed forestry of the kind that supports economies and ultimately supports the whole world depends on such fine-tuned botany. If foresters don’t know what’s what, they can finish up making horrible mistakes. It is still necessary to harvest at least some trees from the wild, and possibly always will be. In temperate countries where the trees in any one forest tend to be of less than half a dozen species (and sometimes only one) it is easy at least conceptually to take a proportion without doing terminal damage. But when the forest contains hundreds of species, and no two next to each other are alike, problems abound. Some tropical trees provide timber of immense value – worth several thousand dollars a cubic metre. Some, which may look very similar from the ground, may be good for nothing but firewood – a
nd yet may be immensely important to the other creatures of the forest. Make a mistake, and you waste time and effort, and do damage for no reason. When valuable trees are harvested, it is important not to take too many and in particular to leave ‘mother trees’ that will seed the next generation. The sad loss of mahogany from the West Indies over the past two centuries is just one example of many of what happens when foresters are careless. Often, though, we find that the target species has relatives that are very similar (and may indeed provide timber that is just as good) but are much rarer. If the forester is careless about identification, he (tropical foresters are usually ‘he’) may harvest the rare, related species alongside the main target species – and so may wipe out the rare one altogether, again with immense and unnecessary ecological damage. Of course, much of the logging in the tropics is still carried out illegally (even in Brazil, where the forest is as well managed as in most places, an estimated 60 per cent of all logging is carried out illegally), and illegal loggers generally don’t give a damn. But the trend to sustainable harvesting is increasing – and depends absolutely on good identification.
But the Amazonian tree known as the angelim, much valued for its fine, strong timber, shows that good identification and careful harvesting are not yet the norm. The angelim is a legume: one of the vast family formerly known as Leguminosae and now called Fabaceae, which includes the acacias and laburnums among trees, and gorse, peas, beans and clover among non-trees. But what exactly is an ‘angelim’? At EMBRAPA, Mike Hopkins has found that foresters apply this hallowed name to well over a dozen different species from at least seven genera. Admittedly, all the commonest ‘angelims’ come from the right family (Fabaceae), but still they come from more than one subfamily from within the Fabaceae.1 Similarly, the excellent timber that is marketed under the general name of ‘taurai’ commonly includes at least five species (and probably many more) from the Brazil-nut family, Lecythidaceae. Perhaps the most notorious confusion of all – much of it deliberate obfuscation – surrounds mahogany. The term should refer to one or at best several species of the genus Swietenia, in the family Meliaceae. In reality an enormous variety of brownish timbers are marketed as ‘mahogany’.
Whatever is identified must also be named. Names are an aide-mémoire but more than that they are vital for precise communication. But after God had expelled Adam from the Garden of Eden, so Genesis tells us, he created the Tower of Babel. Perhaps that was where the trouble began: in any case, naming has always been, and remains, a huge bugbear.
WHAT’S IN A NAME?
Different people speak different languages of course; in aboriginal societies there is commonly one language per tribe, and the world as a whole has many thousands. Since particular species of trees may be widespread, many finish up with a hundred or more different local names – to which travellers, notably Europeans, have been wont to add a few more of their own. For those who simply want to know about trees, and enjoy them – aspiring connoisseurs – this can make life very difficult; although for those who enjoy words qua words, the variety is also most intriguing.
Local names to those who understand their roots are of course instructive: they reflect what the tree means to the people who coined them. Some gave rise to their common English equivalents. The toon tree is tun in Hindi and Bengali. The sacred fig known as the peepul is pipala in Sanskrit – and is also known in English as the bo or bodhi, apparently from the Burmese nyaung bawdi. ‘Tamarind’ comes from the Arabic tamr-hindi, meaning ‘date of India’. Neem is from the Bengali nim or the Hindi nim balnimb. Teak is tek in Tamil. Some local names have simply been adopted straight into English – including, in recent years, the Maori names of native conifers; totara, rimu, miro, matai, kahikatea (which is the tallest tree in New Zealand), and kauri (the most massive New Zealander).
But although local names often mean a great deal to the people who coined and use them they can be of much less use to outsiders. It may be, for instance, that the Maoris recognize some deep similarity, practical or spiritual or whatever, between, say, the kahikatea and the kotukututu, yet see no worthwhile parallel between the kahikatea and the rimu. Certainly, at least to the foreigner, ‘kahikatea’ sounds similar to ‘kotukututu’, while ‘rimu’ is altogether different. You could not guess, as an outsider, that the kotukututu is the tree fuschia, Fuschia excorticata – the only fuschia that still has the form of a (very lovely) tree; and that the kahikatea and rimu are both tall conifers in the same botanical family, the Podocarpaceae. It may be that by not speaking Maori, outsiders miss a great deal that is instructive. But it is at least possible that many local names in Maori and a thousand other languages are not meant to express particular relationships at all. After all, traditional societies – or at least the specialists within them – typically know their local flora and fauna as well as the rest of us know our friends and family. When you know everyone individually, you do not need to name them in ways that express particular relationships. Bill is Bill and Sarah is Sarah and Romesh is Romesh. Why should their names express more than who they are?
Some societies, however, including many Europeans this past few thousand years, have tended to travel the world and have actively sought to find relationships between whatever they came across. I really do not know when such a way of thinking first arose, but Aristotle’s pupil and colleague Theophrastus refers to different kinds of oaks, growing in different places. Even Britain with its paltry inventory of native trees has two distinct native oaks: the common oak, Quercus robur, and the sessile oak Quercus petraea. (‘Sessile’ means ‘sitting’, and refers to the way the cups of the acorn sit directly on the twig – they don’t have a stalk of their own as in common oak.) As European botanists began to travel the world, from the sixteenth century onwards but particularly from the eighteenth, they found more and more oaks throughout Europe, Asia and north America – and up to now have listed a somewhat astonishing 450 different species of oak, including both the deciduous kinds (as the two British natives are) and a host of evergreen types (for example, the cork oak, Quercus suber and the holm oak, Quercus ilex). Although, as we will shortly see, many non-oaks are also casually called ‘oak’, in general the term expresses a true biological relationship in a way that is not always evident in local languages. It’s not that some languages are superior to others. It’s just that different languages serve different purposes. They have different agendas. They express what different people feel is important.
But English and other such global languages raise problems of their own. English names have been conferred by many different groups of people with different traditions and for different purposes: by local people everywhere; and by gardeners, nurserymen, naturalists, foresters, traders, carpenters, makers of pulpits and pianos, and even, in recent years, marketing people. Thus the same tree and its timber may have several different English names (which are often different too in English and American); and also – which can be especially damaging – many different trees may finish up with the same name. It’s as if the word ‘dog’ was also applied as the mood took to horses or ants or goldfish; and goldfish were sometimes called ‘butterfly’ or ‘baboon’.
(Please skip the next four paragraphs if you have no wish to be confused: they are written to illustrate the prevailing confusion.) Thus, the various trees that are peremptorily called ‘tulip trees’ include Liriodendron tulipifera from the magnolia family, Magnoliaceae; and Spathodea campanulata of Africa which is from the catalpa family, Bignoniaceae. But Brazilian tulipwood is Dalbergia frutescens – a member of the Fabaceae (alias Leguminosae), the family of peas and acacias. On the other hand Dalbergia is best known for various species of ‘rosewood’, though of course these have nothing to do with roses, which are in the family Rosaceae. Almonds and plums do belong to the Rosaceae. But the ‘wild almond’ of India is Sterculia foetida, a relative of cocoa in the Sterculiaceae family (now included in the Malvaceae); and the Java plum is Syzygium cumini, in the eucalyptus family, Myrtaceae.
But the populist namers of trees saved their full powers of obfuscation for the conifers. It’s good to acknowledge that members of the Pinaceae family have important characters in common, and to call them all ‘pines’. But foresters and timber traders in particular have applied the term ‘pine’ to just about anything that has needly leaves and is evergreen. Thus, while the Pinaceae predominates among the northern conifers, the two great families of the southern continents are the Podocarpaceae and the Araucariaceae. The Podocarpaceae includes the New Zealand conifers: the kahikatea, the matai, the miro, the rimu. But the pioneer British foresters called the kahikatea the white pine, the matai the black pine, the miro the brown pine, and the rimu the red pine. The Araucariaceae includes three genera: Agathis, Araucaria and Wollemia. Agathis australis, the kauri, is still widely known as the kauri pine. The parana pine, much favoured by do-it-yourselfers, is Araucaria angustifolia from Argentina and surrounding areas. Araucaria heterophylla is commonly called the Norfolk Island pine. (Araucaria araucana is the monkey puzzle tree, from Chile and Argentina.) Even Wollemia, long thought to be extinct and only recently rediscovered in New South Wales, was immediately called the ‘Wollemi pine’ although in modern times we should know better. On the other hand the Scots pine, Pinus sylvestris, which really is a pine, is sometimes known in the trade as redwood; although the trees more commonly known as ‘redwoods’ are the Californian giants of the genus Sequoia, which is now included in the cypress family, the Cupressaceae. But then again, the tree that Californians more commonly call the ‘giant sequoia’ is of the related genus Sequoiadendron (formerly sometimes known as Wellingtonia). Colour is a particular obsession of the timber trade. Trees called ‘blackwood’ come from at least three families – the ebonies, Ebenaceae; the Fabaceae; and the mahogany family, Meliaceae. I won’t even begin to bore you with the number of species and their timbers known as ‘whitewood’.