The Tree (25 page)

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 beautiful, 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.

There are 35 or so known species of southern beeches, although in reality there are probably many more. Most are evergreen, although a couple are deciduous. Nine live in South America, not least in the bands of forest along either side of the Andes in Patagonia, which are dominated largely by the lenga
(N. dombeyi)
and the nire
(N. procera)
and are home to pumas, guanacos (small relatives of the llama), southern river otters, geese, Andean condors, and deer. Here is another grand place to see and wander through, now sadly threatened by too much logging, although in part protected now by Patagonia’s Perito Moreno National Park. Three more southern beeches live in Australia. They were far more widespread there when Australia was wetter, but in these dry and fire-prone times they are largely supplanted by eucalyptus. They flourish still in New Zealand (four species); and there are eighteen more in New Guinea, New Britain, and New Caledonia (inevitably!) and a few more on other islands. There are none in Africa, but before Antarctica drifted to the South Pole and was buried in ice it clearly had great forests of southern beech. Often, within their range, they are the dominant broad-leaved trees, but in New Zealand and South America, in particular, they tend to share their forests with the great southern conifers, the podocarps and the various araucarias. Though we can reasonably suggest that southern beeches are the southern equivalent of the oaks, beeches, and chestnuts of the north, in truth the southern temperate forests tend to be very different in character: typically damper and, in New Zealand, having a wondrous understory of giant ferns, each worthy to stand in some stately conservatory in a grand ceramic pot.

Challenging the Fagaceae family in diversity and ecological range (although nothing can quite challenge the Fagaceae) is the family of the birches, alders, hazels, and hornbeams, the Betulaceae. Again, all of them are trees and shrubs, widespread in the Northern Hemisphere—both in temperate regions and in the most extreme north. Just a few, notably some alders
(Alnus),
drift into the Southern Hemisphere. In general, trees of the Betulaceae are early on the scene when there is new ground to be colonized—and so they rapidly spread north after the last ice age, in the wake of the retreating glaciers. In the case of alders, they are helped in this by nitrogen-fixing
Frankia
bacteria in nodules in their roots. Alders in particular, too, largely because of their nitrogen-fixing bacteria, do well in waterlogged soils, in the same way as mangroves. Sometimes, however—as with the endless birch forests in Siberia and Canada—Betulaceae are the dominant forest trees. Their flowers are catkins, pollinated by wind; and their seeds are mostly distributed by wind (or water, in the case of alders and hop hornbeams); but the seeds of hazels are spread by rodents, with squirrels as key players, although they exact a huge fee for their services.

Judd recognizes 6 genera, with a total of 157 species: 60 birches
(Betula);
35 alders
(Alnus);
35 hornbeams
(Carpinus);
15 hazels
(Corylus);
ten hop hornbeams
(Ostrya),
also sometimes called ironwood; and a couple of
Ostryopsis,
which resemble hop hornbeams. Early botanists placed alders, birches, and willows together in a subfamily they called Amentiferae: all, after all, are trees, and have catkins. Walnuts, figs, and elms were bundled in too, for good measure. But the catkins that they all shared evolved independently, not from a single common ancestor. Alders, birches, and willows do share a propensity as pioneer species, however, and are used for similar things—not least to provide the charcoal needed to make gunpowder.

Helped by their nitrogen-fixing bacteria, alders grow rapidly, sometimes reaching 30 meters in a decade—and so aggressively that they are often rated as weeds. They definitely have their upside, however. Because they fix nitrogen, they are able to improve the soil significantly, and so benefit the whole forest. They are excellent pioneers; in general they are widely planted, and in particular are pressed into service for soil reclamation.

Though Judd recognizes 35 species of alder, this should not be taken as gospel. Stephen Harris, curator of the herbarium in Oxford University’s Department of Plant Sciences, puts the figure at nearer 25. But as outlined in Chapter 1,
Alnus
is one of those genera in which the concept of “species” is hard to pin down. They have a great tendency to form polyploid hybrids, and given the enormous geographical range of
Alnus,
and the remoteness and hostile nature of many of the places it tends to live, we can also be fairly sure that many species remain to be identified.

For alders are indeed extremely widespread.
A. acuminata
lives in Central America and extends into the highlands of South America, and is planted extensively for timber and fuel. The black alder,
A. glutinosa,
is widely distributed in Europe. In workaday mode, it serves to stabilize riverbanks and roadsides, and is grown for fuel. More grandiosely, it once supplied much-valued timber for violins. In recent years, however, at least in Britain, black alder has suffered hugely from attack by the fungus-like
Phytophthora cambivora,
related to potato blight. The Nepal alder of the Himalayas,
A. nepalensis,
is also planted widely for timber and firewood, and as forage for cattle and sheep. The red alder of the American northwestern floodplain,
A. rubra,
is a huge tree, up to 40 meters, favored for building and furniture, as well as for fuel and pulp (though used mainly in mixtures). Red alder can also be a significant weed in plantations of pines. Alders do well in waterlogged places. Alders are among the many trees that tend to concentrate minerals within their cells: they pick up gold, for instance. Whether it is worth trying to extract gold from them, I do not know. Alder bark is also astringent and is traditionally used to treat burns and infections.

The oldest known fossils of alder date from the Miocene, around eighteen million years ago. The genus
Betula
is much older: birch fossils date from the Upper Cretaceous, still in dinosaur times, and perhaps birches were most diverse in the Eocene, around forty-five million years ago. The 60 or so extant shrubs and trees also live in even more diverse habitats than alders do, from temperate lands to the extreme northern limit of trees. They are present and may be dominant in peat lands: along the banks of streams and the shores of lakes; in damp woods; on the margins of roads and railways; in alpine settings; and on tundra. Birches are pollinated by wind—and produce a great deal of pollen. Like alder pollen, this is bad for hay fever, though speaking as a sufferer, I find it a small price to pay for all that beauty. Again, birches tend to be polyploid, and prone to hybridizing.

Fey, melancholic, and wonderfully hardy: the birch.

Birches are good biochemists—and so are used for many things besides their attractive white timber. Their leaves are often rich in resins, and their bark (particularly from the white-barked kinds) is rich in phenolics. Some species produce betulin in their bark, which makes them waterproof. (These agents are also said to be effective “antifeedants,” repelling hungry browsing animals in winter; yet many insects feed on birch, and fungi may rot the heartwood.) Their twigs were traditionally used for punishing: the generic name
Betula
derives from the Latin for “beat.” Birch bark (for example, of the paper birch,
B. papyrifera
) is used for roofs and canoes, and is the stuff of the oldest known Hindu manuscripts, dating from around 1800
B.C.
It is also rich in oil and starch and serves as food in times of famine. Like alder and willow, birch wood burns to make good charcoal, excellent for gunpowder (how many did the Russians fell in seeing off Napoleon?). The sap of the Appalachian
B. lenta
is tapped in the spring and fermented to make birch beer. Oil of wintergreen, containing methyl salicylate (related to aspirin), can be obtained from
B. lenta
and the yellow birch,
B. alleghaniensis.
The leaves of the European species downy birch
(B. pubescens)
and silver birch
(B. pendula)
produce a green dye. Birch, like alder, accumulates heavy metals in its leaves and can be used to reveal their presence in the soil beneath. Birches in general yield valuable timber, and also pulp. Many birches are grown as ornamentals, and quite right too.