The Tree (13 page)

Members of the genus
Thuja
are long-lived and cypress-like. The grandest of all the five species is
Thuja plicata,
known confusingly as the western red cedar—the “cedar” of the timber trade: fabulous all-weather wood that makes fine garden furniture and shingle roofs that will last a lifetime without further preservation. For good measure, too, its timber (as in most species of
Thuja
) is aromatic, and its leaves when crushed smell of pineapple. In its native Oregon, Washington, and British Columbia, western red cedar grows to 60 meters, with great buttressed bases that can be 10 meters across. The Native Americans of the northwest coast salvaged its long-dead trunks from the swamps and hollowed them into vast canoes and totem poles; and the Haida Indians of the shores of southern Alaska carved arrows from the stems, fashioned the tough knots into fishhooks, and wove the fibers from the bark into ropes, baskets, mats, clothes, and hats. In more humble guise, western red cedar features in suburban gardens, filling the same kind of role as Lawson’s cypress. But the first
Thuja
to make it to Europe—to Paris, in the sixteenth century—was America’s other native: the smaller
T. occidentalis
from the eastern states.

The most widespread of all conifers: one of the many junipers.

Three more species of
Thuja
live in northeast China, Korea, Japan, and Taiwan. This is a common pattern of distribution: many trees of many kinds—including oaks—are distributed both in North America and eastern Asia, notably China. They seem for some reason to have found it easy to straddle the Pacific. In any case, trees do not respect political boundaries and, indeed, reveal how arbitrary the lines that we draw on maps really are.
Thuja
trees in general like it cool and moist, and grow from the coast to the hills. Though most are tall there is one,
T. koraiensis,
of northeast China and Korea, that grows on exposed mountain ridges as a twisted shrub, showing again that any one group of organisms may essay a great variety of body forms.
T. sutchuensis
is one of those conifers that was presumed to be extinct but then turned up. To be sure, it didn’t go missing for quite as long as
Metasequoia
or
Wollemia,
but it was thought to be long deceased until the late twentieth century, when some were found alive and well in the Daban Shan mountains of northern China.

The genus
Thujopsis
has only one species, from Japan, which can look curiously like a plastic imitation of a cypress. It also favors cool, moist places, from the coast to the mountains, and is another conifer that grows slowly at first in shade but eventually overtops its neighbors.
Thujopsis
comes in various cultivated varieties and is much favored in gardens.

The four species of
Widdringtonia
are among the few conifers that put in an appearance in sub-Saharan Africa: in South Africa, Malawi, Mozambique, and Zimbabwe.
Widdringtonia
are fire-adapted: they do well when the surrounding shrubs are cleared by fire, as happens regularly in the African summer. The genus has been sadly depleted by felling, however. The forests of “Mulanje cedar” on the steep slopes of Malawi’s Mount Mulanje are the only substantial stands of
Widdringtonia
left to us. They are on my wish list of trees to be seen in the wild.

Two other genera of the old-style Cupressaceae are worth particular mention. Both have only one species each, both of which can grow into very large trees. They are
Platycladus
of eastern and northeastern China, Korea, and the Russian far east; and
Taiwania,
which, of course, occurs in Taiwan and also in China (Yunnan), Myanmar (Burma), and Vietnam—where it was discovered only in this century. It grows up to 70 meters. The businesspeople and diplomats who flock to Taiwan probably feel they have little time for trees. A pity. Perhaps they should make time.

Of the eight genera that once formed the Taxodiaceae family, five have only one species each:
Cryptomeria, Glyptostrobus, Metasequoia, Sequoia,
and
Sequoiadendron.
Of the other three genera,
Athrotaxis
has three species, while
Cunninghamia
and
Taxodium
have two apiece. This gives a grand total of twelve species. Here is a bunch of relicts indeed—magnificent, most of them—but not much left from a group that once bestrode the Northern Hemisphere.

Cryptomeria japonica,
the “Japanese cedar,” known in the trade as “sugi,” accounts for much of the remaining forest in Japan. Yet those forests are probably not natural; rather, they represent the remains of some of the oldest forestry plantations in the world. The timber turns dark green when buried in the ground, to produce
jindai-sugi,
which serves as a semiprecious “stone.”

Three genera of redwoods are left to us: the coastal redwood
(Sequoia),
the giant sequoia
(Sequoiadendron),
and the dawn redwood
(Metasequoia).
Truly the remaining redwoods are relicts, for 100 million years ago, when the climate was much milder and flowering plants were first coming into their own, there were a dozen more species of redwood throughout western North America, Europe, and Asia. There was even one in Australia. Various species of
Metasequoia
were widespread in the Tertiary. In the Eocene, around 45 million years ago, when all the world was wonderfully warm, they grew far up in what is now Arctic Canada, only 10 to 15 degrees from the North Pole. But then the world began to cool, in what has been called an “icebox effect”—prompted by a steady diminution of atmospheric carbon dioxide—and by the time of the Pleistocene (around 2 million years ago), the genus almost went extinct. Now, only the dawn redwood is left to us:
Metasequoia glyptostroboides.
Even this was presumed to be extinct, until a few turned up in central China in the 1940s. It’s hard to say exactly how the last dawn redwoods in the wild have been scratching a living since the time they went missing, because the area around their present habitat has been so cultivated this past few hundred years; but in general they seem to prefer the same kind of niche (wet) as the swamp cypress,
Taxodium.

The genus
Sequoia
is also reduced to a single species:
S. sempervirens,
the coastal redwood of western, lowland California and Oregon. Yet the genus was once present in three continents (of which one was Australia).
S. sempervirens
needs the coast. It gets about a third of its water from the fogs that rise almost daily from the cold currents of the North Pacific and condense against its dark green, leathery, feathery leaves. Some coastal redwoods are managed for timber on a one-hundred-year cycle; their rich reddish brown wood provides everything from telegraph poles to coffins and organ pipes, while the fireproof bark, up to 20 centimeters thick, supplies fiber for fiberboard.

There is only one species of
Sequoiadendron
left to us, too: the giant sequoia
(S. giganteum),
which survives in groves on the western slopes of the Sierra Nevada in California, sometimes in pure stands and sometimes with other conifers. Like
Sequoia, Sequoiadendron
once included several species, widespread over North America. Like
Sequoia,
too, it is adapted to fire, and in general regenerates only after fires, so that there are successive waves of new recruits, each following a fire. It grows quickly when young, soon overtops its rivals, and may live for thousands of years—not as tall as the coastal redwood, but sturdier. On the face of things,
Sequoiadendron
seems a fine survivor. Yet it is down to one species, in only one small restricted area. Nature is unpredictable.

The old-style Taxodiaceae family takes its name from
Taxodium,
the genus of the swamp cypresses. They generally live, as their name suggests, in swamps and on the waterlogged fringes of lakes. Their roots have vertical outgrowths that project above the ground or the surface of the water, which apparently act like the ventilator pipes on the decks of ocean liners, bringing air, with its much-needed oxygen, down to the roots. The broad-leaved trees of the mangrove swamps have a comparable arrangement. In Mexico, however, swamp cypresses sometimes grow well above the water table, sometimes in the company of broad-leaved trees. Again, a once-various genus is now reduced to two species:
T. distichum,
of the southeastern United States, which is deciduous, and
T. mucronatum,
of Guatemala, Mexico, and southern Texas, which is reported to be evergreen.

Finally, closely related to
Taxodium
is its Asian equivalent,
Glyptostrobus,
also reduced to a single species that grows along streams and in other damp places, including river deltas, in southern China and Indochina. Again we see the North American–Chinese connection.

P
INES
, F
IRS
, S
PRUCES
, T
RUE
C
EDARS
, L
ARCHES
,
AND
H
EMLOCKS
: F
AMILY
P
INACEAE

Pinaceae is not the biggest family when measured in genera—a mere eleven—but it does have the most known species, with 225. This may simply be because of all the conifers, the Pinaceae are the best described. This is partly because the three biggest genera include the most economically valuable trees of all—the pines
(Pinus),
the firs
(Abies),
and the spruces
(Picea)—
and partly because all but one species of the Pinaceae are native to the Northern Hemisphere, where most scientists do their work. The only one of the family that has strayed south of the equator is
Pinus merkusii,
from northern Sumatra (note the similarity to junipers, which also have just one southern species). Even the fossils of the Pinaceae are exclusively northern. It is unclear, as we have seen, where most of the conifer families originated, but the Pinaceae family seems emphatically Laurasian.

The Pinaceae as a whole live in many habitats, but when it’s very dry they tend to be replaced by Cupressaceae; only a few pines can take extreme aridity. Firs, larches, spruces, and pines are among the most extreme northerners among trees; they are found along the northernmost tree line in Eurasia and North America and climb mountains as high as any tree will go. Sometimes they grow alongside broadleaves—especially pines, which are pioneers, and firs and hemlocks
(Tsuga),
which tend to creep in later.

The biggest natural forests of Pinaceae are in the extreme north—North America, Scandinavia, and Russia. Yet these boreal forests contain very few different species. As with most groups of creatures, the greatest diversity is toward the equator, where the growing season is longer and there is abundant seasonal rain. There are also mountains toward the equator, which create boundaries between populations, which, when thus isolated, evolve into new species.

In practice the various Pinaceae are focused mainly in four great centers of diversity (although we might with justice add a fifth). Two of these centers are in Asia, which has the greatest variety of genera; and two (or three) are in North America, which has fewer genera but has the greater number of species, though mainly from the genus
Pinus.

The greatest of the four centers—with species from all eleven genera—runs from China through to the Himalayas (Sichuan and Yunnan to Nepal). Most various among them are the firs and the spruces. Several genera are endemic to China:
Cathaya, Nothotsuga,
and
Pseudolarix.
Japan and Taiwan form another, separate center, with species from ten of the eleven genera. The one lacking is
Cedrus,
the genus of the true cedars.

Of the North American centers, California has five genera:
Abies, Picea, Tsuga, Pseudotsuga,
and
Pinus.
Mexico, a separate center, has the lion’s share of
Pinus,
with forty-three species, and also has
Abies, Picea,
and
Pseudotsuga.
Perhaps Mexico has so many species of
Pinus
because it has so many natural fires, and pines are good fire resisters—indeed, they are dependent on fire: they cannot release or germinate their seeds without it. Finally, the Atlantic plain of the southeast United States really forms yet another center, with an array of pines that is largely different from those of California and Mexico.

With 109 known species,
Pinus
is the largest genus of all the living conifers (with
Podocarpus
running a close second). It also seems to be the oldest known genus of Pinaceae. Most genera of the Pinaceae date only from the early Tertiary—60 million years ago or less. But fossils of
Pinus
are known from well before the Tertiary. The earliest date from the Cretaceous, the last great age of the dinosaurs. Many
Pinus
species were more widespread in former times than they are today, yet they have not retreated as the sequoias or the araucarias have done. Features that distinguish
Pinus
include the papery sheath that surrounds the base of their needle leaves—leaves that sometimes are borne singly, but more often in clusters of up to five. Yet their overall form is highly various. Most grow tall with a central trunk; some are more spreading like cedars; and some are multistemmed shrubs.