The Tree

by Colin Tudge

  Then comes a huge and supremely important family: the Moraceae. Its 53 genera (1,500 species) include shrubs, climbers, and herbs—but also some intriguing and supremely important trees that grow throughout the tropics as key players in rain forests. The jackfruit or breadfruit (Artocarpus) has a pale grayish-green warty-skinned fruit that is really a fused mass of fruits (an infructescence) and may be huge: as big as a sack of coal and up to ninety pounds in weight. Brosimum is the breadnut. There are some fine timber trees, too: the iroko (Chlorophora excelsa) from central and western Africa is often used as a substitute for teak. The snakewood (Piratinera guianensis) from tropical America is extremely heavy (much heavier than water when dried), with a black-brown tortoiseshell pattern favored for everything fancy, from the backs of brushes and umbrella handles to violin bows—and for native bows for shooting arrows. More temperate is the mulberry (Morus): the white kind grown to raise silk moths (nine thousand pounds of leaves for one silk blouse), the black kind favored for its glorious edible blackberry-like fruits, popular from the seventeenth century and now featured, gnarled, in many an old walled garden.

  Then there is Ficus, the genus of the figs. Ficus seems to go out of its way to be extraordinary. First, it is enormously various, with about 750 known species: a huge presence throughout the tropics, primarily in tropical rain forests, but reaching too into the subtropics and Mediterranean. Then there is the way it grows. About half the species simply take root in the ground like most other trees. The other half begin their lives as epiphytes—plants that grow on other plants. The seed lodges in the fork of a branch of some forest tree or, often, in the severed leaf base of some palm or, sometimes, in a crevice in a wall. As it grows, as an epiphytic cactus or orchid might, it sends down roots toward the ground; these eventually take root on their own account. Then the once-dangling roots function as stems: where previously they had carried nutrient and water downward, from the epiphytic roots above, now they carry minerals and water upward, from the new roots in the ground below. Generally the dangling root-stems fuse with one another to form what looks like an exercise in macramé: you wind up with what may be a massive trunk that you can see right through. In the epiphytic figs known as “stranglers” the probing roots twine around the host trunk. In others, like the Indian banyan, F. benghalensis, there is less obvious entwining. The roots merely drop to the ground eventually to form multiple trunks. The throttling of the stranglers, the monstrous weight of the epiphytic fig as a whole as it grows (whether it strangles or not), and the blotting out of light eventually kill the host—although the obliteration may sometimes take a century or more, until which they live in grisly union.

  Banyans form new trunks by sending down roots from above.

  Many trees are sacred to the Hindus and Buddhists of India, and two of the epiphytic figs are among the most sacred of all. The British in India were often cavalier, but on the whole, I am told (by Indians), they respected the sacred trees, and many ancient ones remain even in the heart of British enclaves—including one magnificent specimen (albeit split into two by a storm in 1947) in the Forestry Research Institute at Dehra Dun, at the foot of the Himalayas. The FRI was established at the turn of the nineteenth century on the site of what had been twenty-two villages (although many of the village people stayed to work at the institute, and many of their descendants still do). The indigenous vegetation was largely cleared—but this great banyan, dating at least from the eighteenth century and probably before, was spared. The greatest of all, in Calcutta, is reputed to be a quarter of a mile in circumference, with hundreds of trunks connected overhead to form a colonnade, able to provide shelter for twenty thousand people. The roots are guided to the ground along sticks.

  Most sacred of all the figs, however—most sacred of all trees indeed—is the peepul, F. religiosa, also known as the bo. For it was under a bo tree that the young Prince Siddhartha sat and meditated, sometime in the sixth century B.C., and received enlightenment, and thenceforth was known as the Buddha. Peepul trees are unmistakable. The leaves of many tropical trees have “drip tips”: extensions at the end that act like gargoyles, quickly getting shot of surplus rain. The bo leaf is heart-shaped, typically about the size of a man’s hand, and its drip tip is enormous, about a third of the total length. This form, so characteristic, has become a Buddhist icon; bo leaves often provide the background to pictures of the Buddha. Yet they grow like the humblest nursery clone by the side of Indian roads—or sometimes right in the road, with oxcarts and brightly painted, black-smoking lorries milling in the dust around them. In India, sacred means sacred. The traffic gives way.

  Most extraordinary of all, however, is the manner of the figs’ reproduction. The flower, or rather inflorescence, is a fleshy cup formed from the flower stem; and within that cup hundreds of flowers open inward. The whole apparatus is pollinated by minute wasps: extreme specialists, for there is one dedicated species of wasp for each of the 750 species of fig. At least, “one fig, one wasp” is the general rule. The reality is turning out to be more complicated and even more fantastical, and is discussed at length in Chapter 13.

  Finally comes a pair of closely related families—the Urticaceae and the Cecropiaceae. The Urticaceae is the family of the nettles—which northerners know as herbs with a serious line in stinging (and which are also fine sources of fiber)—but it also includes some tropical forest trees, some of which also sting. In Queensland I was told the tale of a well-known British botanist much given to the waving of arms who waved them a little too much, right through the branches of a nettle tree, and wound up in hospital.

  Cecropiaceae is a most intriguing family; it includes the tropical genus Cecropia. Cecropias are pioneer trees par excellence, with hollow stems like bamboo for extra-rapid growth, branching at the top to produce an umbrella of silvery-gray compound leaves roughly like a horse chestnut’s. In the hollow stems dwell ants, which, as in acacias, are the tree’s housekeepers. In newly exposed land the cecropia provides almost instant shade, while its leaves, roots, and latex are pharmacologically potent and are used to treat a range of conditions, from hypertension and depression to gastric ulcers. In tropical America, three-toed sloths are fond of cecropias: sloths seem remarkably common, and all the ones I have seen (all, as it happens, in Panama) were in cecropias. But cecropias can bring bad news, too. Their silver foliage stands out in the forest, and since they grow fast in open space they show where gaps have recently formed. Some of those gaps are legitimate: old trees die naturally, and in some areas at least, favored forest trees are selectively and carefully harvested. But often you see hillsides where no logging is allowed awash with cecropias; they reveal where the illegal loggers have been at work. In Brazil and elsewhere, such sights are all too frequent.

  The Cecropiaceae family, as now defined by Judd, also includes Cannabis, provider both of hemp fibers and of marijuana, and Humulus (hops). This is how the molecular studies suggest they should be classified. In the past, however, Cannabis and Humulus have commonly been placed together in a separate family, Cannabaceae, which in turn has been grouped together with the Urticaceae within their own order, the Urticales. Urticales in turn has sometimes been associated with the witch hazels in the hamamelid group (now disbanded), and sometimes placed in the Malvales order, of which more later. Cecropia has been shuffled uncertainly between the Urticaceae and the Moraceae. For the time being things are as described here, with hemp and hops grouped with Cecropia in their own family, Cecropiaceae, among the Rosales. Let us hope it stays that way. Cannabis and nettles both produce fine fibers, good for ropes, though nettle ropes are not common these days.

  OAKS, BEECHES, BIRCHES, HAZELNUTS, AND WALNUTS: ORDER FAGALES

  Within the eight families of the Fagales order are some of the most beautiful, most iconic, most treasured, and most ecologically and economically significant of the temperate broad-leaved trees: the oaks, beeches, chestnuts, southern beeches, birches, alders, hornbeams, hazels, she-oaks, bayberries, walnuts, pecan
s, and hickories. Estimates of the total species vary wildly: Judd suggests 1,115, but there could be many more, not least because many of the Chinese kinds, where the order abounds, are as yet largely unstudied. All members of Fagales are trees or shrubs; there isn’t an herb in the entire order. The oldest fossils (of pollen and other parts) date from around 100 million years ago, when the dinosaurs were still in full pomp. Where they arose is a bit of a mystery. The oldest family of all seems to be that of the southern beeches (Nothofagaceae)—but they are the only Fagales family that lives in the Southern Hemisphere. All the rest are based in the Northern Hemisphere, with just a few venturing south of the equator here and there. But then, the evolutionary history of all groups is full of loose ends.

  The Fagaceae family includes the best-known trees of the Fagales order, and the most important economically and ecologically. The family probably first arose around ninety million years ago in tropical mountains—near the equator but nonetheless a relatively cool habitat—and it extends through the Northern Hemisphere from temperate lands to the tropics. All are trees or shrubs, rich in tannins. All have fruits in the form of a nut, with a spiny or scaly capsule around the outside—sometimes fully enclosing the nut, and sometimes holding it decorously like an egg in an egg cup.

  Botanists tend to define and include around nine genera within the Fagaceae. The oaks, Quercus, are the biggest genus, with 300 to 600 species, depending on who’s counting (Judd opts for 450). It seems, though, that many of the Asian oaks should be placed in the tan oak genus, Lithocarpus, which at present contains around 100 to 200 known species from North America, with only one officially recognized from Asia.4 Fagus is the genus of the beeches, with about ten species. Castanea, the chestnuts, also has about ten species. Castanopsis, which in some classifications embraces Chrysolepis, includes the 150 or so species of chinkapin (or chinquapin), from North America, China, India, and the Malay archipelago. There is just one species of Colombobalanus, from Colombia, in South America; and two of Trigonobalanus, from China and Malaysia. About one in eight of all the species of Fagaceae—12 percent—are included in the 2003 Red List of Threatened Plants.

  Northern Europeans and Americans think of the genus Quercus as mighty trees of temperate lands that shed their leaves in winter. This is true of Britain’s two native oaks, the English or common oak, Q. robur, and the sessile oak, Q. petraea: and those two, plus ash and Scotch pine, would now extend from the tundra of northern Scotland to the tip of mild and rainy Cornwall were it not for our forebears, who stripped the post–ice age forest to make farmland and took the oaks in particular to build the medieval and Tudor cities, and the navy that defeated the Armada. (“Heart of oak are our ships,” we used to sing at school in moments of patriotism. But later, the British navy made much use of teak, from India.)

  The oaks are the most widely distributed of forest trees—and not particularly northern. Indeed, common and sessile oak are the only species that venture more than 50 degrees north of the equator (and those two extend up to 60° north). Evolutionary studies suggest that Quercus first appeared in Southeast Asia, around 60 million years ago,5 and most still live between 15° north and 30° north, especially in Mexico and Central America, and in the Yunnan province of China. In the south the genus peters out in Colombia (where oaks live in the highlands) and Indonesia. North America has the most species; Europe and Asia have many; and a few live in North Africa. Between them the different kinds are adapted to every habitat, from desert to swamp and from sea level to the highlands—up to 4,000 meters in Yunnan—as high as the highest Rockies. In the wild, the most widespread of all the individual species are red oak (Q. rubra) and white oak (Q. alba) in Northern America; Q. acutissima and Q. mongolica in Asia; and common and sessile oak in Europe. Many are shrubs. Many—like the live oaks (Q. agrifolia and Q. wislizenii) of California; Q. coccifera; holm oak (Q. ilex); and cork oak (Q. suber) of southern Europe—are evergreen.

  Oaks are so tremendously successful partly because, like many other successful trees, they can reproduce in so many ways. Unlike most Fagaceae, but like beeches and southern beeches, oaks are pollinated by wind, and generally bear both male and female single-sex flowers on the same tree (that is, they are monoecious). In good years the acorn crop is prodigious; they are distributed largely by mammals (especially rodents). But oaks also sprout from damaged trunks, to form natural coppices; and coppicing once supported entire industries of foresters (broadly defined) throughout Europe. Oaks also send forth shoots after forest fires, again producing entire stands that are clones of the parent individual.

  Nowadays, of course, many have been transplanted from their native lands and have become ubiquitous: red oaks, from the eastern United States, are planted throughout Europe; common oak, from Europe, is now seen just about everywhere; and so on. The timber of many species is of legendary strength and beauty and is used for everything from pit props in mines to the finest veneers. Half of all hardwood in the United States comes from oaks. Their wood burns well: oak chips are essential for smoking kippers. Oaks are burned for charcoal, too. They make some of the finest barrels, most favored for sherry and whiskey and wine. Their tannins are used for tanning leather. Cork oak has a thick fireproof layer of cork beneath its bark, a key player in the traditional economies of Portugal and Andalucia, the plantations not only providing cork but also a home for the black pigs that produce such magnificent hams: a fine exercise in agroforestry. Entire streets in Andalucia are lined with shops that seem to sell hams exclusively. The young piglets are ginger-brown and trot about in tightly coordinated squads as baby warthogs do. You meet them on Iberian hikes—torn, as wild animals so often are, between curiosity and nervousness: charming, fleeting companions. The cork forests, too, are home to some of the last of the Spanish lynx. Natural cork is now threatened by plastic: yet another degradation of the world’s ecological and cultural diversity.

  The tan oaks, Lithocarpus, have fruits like acorns but leaves like a chestnut’s. Tan oaks are less legendary than oaks; but they, too, produce hard, strong timber—though mostly used for pulp and firewood—and their tannins also are used to tan leather.

  Seven of the ten or so species of beeches in the genus Fagus live in temperate eastern Asia. There is also one in North America, one in Europe, and one in the Caucasus. Normally they are found with other deciduous species in mixed forests, in temperate climes with soils that hold moisture well but are not waterlogged, for they like neither flooding nor drought. But they don’t mind shade and will grow for decades in the shadow of other trees. So it is that the European beech, F. sylvatica, grows happily alongside sessile oak, common oak, and the European hornbeam, Carpinus betulus. On plantations, hornbeams are grown with beeches to “train” them—encourage them to grow straight and tall, and to shed their lower branches as they reach up. The American beech, F. grandiflora, features in about twenty different forest types in the eastern United States, sometimes dominant but by no means always. Its companions typically include hickories and oaks, yellow birch, sugar maple, red maple, American basswood, black cherry, plus eastern white pine and red spruce; and in the south, it may grow alongside Magnolia grandiflora (another combination I would very much like to see in the wild, and haven’t yet). All in all, beeches seem to be sociable trees. They are also long-lived. Among American broadleaves only the white oak and the sugar maple are said to live longer.

  Beech, like oak, is highly prized, its silky, pale timber excellent for floors, furniture, veneers, turning, and steam bending. Beech that has been infected with fungi may be particularly valued for turnery, with wiggly black lines etched by the fungus in the creamy wood. There is a parallel here with noble rots, and with the yeasts and molds that produce the world’s great wines and blue cheeses: one of the great leitmotifs of Western art is that beauty and decay are never far apart. People as well as wildlife eat the nuts, or mast, of beeches. I have waited in traffic in Holland while pigs snuffled beech mast off the road (and rightly so). Beeches are beau
tiful, too. Their trunks are smooth gray columns. Their diaphanous leaves filter the light like pale green glass. Some garden varieties are stunning, like the copper beech (in truth, deep red) and the weeping kinds that grow like spheres, their branches sweeping the ground if browsing animals are kept at bay. They also make fine hedges—their leaves turn red-brown in winter but nonetheless remain on the hedge (although beeches that are allowed to grow into forest trees shed their leaves). Altogether, Fagus is a fabulous genus.

  One of the temperate world’s most valued hardwoods: the beech.

  The ten or so species of the genus Castanea are the sweet chestnuts. They are also known in some parts as chinkapins (but so are Castanopsis and Chrysolepis). Sweet chestnuts hail naturally from southern Europe, North Africa, southwestern and eastern Asia, and the eastern United States. They are prized for their nuts, of course: traditionally roasted, and also the source of a fine stuffing, excellent with wintry goose. Before the 1930s, too, the American chestnut, C. dentata, was prized for its timber. But American chestnut is one of all too many trees that have been devastated by disease: in this case the chestnut blight, Endothia parasitica. As with Dutch elm disease, the fungus attacks larger trees, so American chestnuts are at least able to grow to the size of a shrub before the stems are killed. The roots survive, the stems regrow until they are big enough to be zapped again, and so on ad infinitum. It is all immensely sad.

  The southern beech, the genus Nothofagus, first attracted the attention of Joseph Banks in the late eighteenth century, during his trip south with James Cook. In the 1830s, the young Joseph Dalton Hooker was struck by the similarities between different southern beeches on different continents. In particular, New Zealand’s tawhai or silver beech, N. menziesii, much favored for its timber, is remarkably similar to Australia’s N. cunninghamii, another fine timber tree, confusingly if typically known as the Tasmanian myrtle; and also to N. betuloides of South America. Such observations fed the growing suspicion that different species in different places must have evolved from some common ancestor. (Hooker later became great friends with Charles Darwin, another pioneer naturalist in southern climes, and succeeded his father, William Hooker, as director of Kew.) Botanists for many years placed southern beech among the Fagaceae, alongside beech. But the cups that enclose the nuts of beeches, oaks, and chestnuts are formed from the flower stalk, while those of southern beech are compacted from bracts. So the relationship is not as close as it may seem, and southern beech now has its own family, Nothofagaceae, although still within the order Fagales. Nothofagaceae is the only Fagales family that belongs to the Southern Hemisphere.