Alerce: The South American Giant

In the primeval rainforests of Chile and adjacent Argentina lives an ancient tree

Imaging walking through a magnificent cathedral forest with giant trees looming overhead--each one six to twelve feet in diameter. The dominant ones are from 1,500 to 4,000 years old, and the forest wood contains more carbon than any other, save perhaps some of the most superlative coastal California redwood groves. Below the giant trees is a lush evergreen growth of southern beech, laurel, and myrtle trees. Below these are brilliant flashes of scarlet, white, and blue from native Fuchsia, and myriad vines and woody shrubs. The forest resounds with a host of bizarre-sounding birds and mammals, most of them unique to this part of the world. As we near the twenty-first century few scientists or naturalists even know the names of these trees, much less the significance of this unique forest! This is the enigma of South America's oldest trees--the alerce (pronounced ah-LER-say).

So what is the scientific significance of alerce, and why should scientists spend the time and effort required to traverse one of the world's most remote and impenetrable forests to study it? The alerce is one of the most compelling examples of parallel or convergent evolution with the conifer forests of the Northern Hemisphere. Studying it may be the ideal opportunity for testing ideas about how forests have evolved in the face of changing climates and have adapted to these stresses. Perhaps this information could help form the foundation for understanding the implications of global climatic change.

Charles Darwin and the captain of the Beagle were among the first European naturalists to discover the alerce in 1832, and he recorded his impressions while exploring the southern South America coastline on Chiloe Island and San Pedro Island:

From a distance the view somewhat resembles that of Tierra del Fuego [southern tip of South America]; but the woods, when seen nearer are incomparably more beautiful. Many kinds of fine evergreen trees, and plants with a tropical character, here take the place of the gloomy beech of the southern shores.

In the lower part of the mountain, noble trees of winter's bark, and a laurel like the sassafras with fragrant leaves and others the names of which I do not know, were matted together by a trailing bamboo or cane. On the higher parts, brushwood takes the place of larger trees, with here and there a red cedar or an alerce pine. (Charles Darwin, Voyage of the Beagle, 1845)

The alerce still remains relatively unknown today partly because of the remote and inhospitable habitats it occupies. As Darwin noted, "In the winter the climate is detestable and in the summer it is only a little better. I should think there are few parts of the world, within the temperate regions, where so much rain falls. The winds are very boisterous, and the sky almost always clouded." Rain occurs during every month of the year and usually totals 160-270 inches within the alerce region. The alerce only occurs in the northern portion of the Chilean temperate rain forest zone and in adjacent Argentina. In total it covers only four degrees of latitude, a small remnant of its former range throughout much of temperate South America.

The alerce tree, which has variously been classified as a pine, a cedar, or a member of the redwood family, is still somewhat of an enigma to taxonomists today. The common name is Spanish for larch (an unrelated member of the pine family [Larix]), while the scientific name is Fitzroya cupressoides, in honor of the captain of Beagle, Robert Fitzroy. Cedar itself is not a particularly clear botanical term. The "true" cedars are found only in the Middle East and northern Africa, have needle-shaped leaves, and are members of the pine family. What Americans call cedars are actually members of the cypress family.

Alerce is classified as a cypress (the Cupressaceae) but has many characteristics of the closely related bald cypress family (which includes both the giant sequoia and redwood). Its closest relative is an obscure shrub which occurs at high elevations in Tasmania, Dislema archeri. Alerce has small, scalelike leaves and small, rounded cones reminiscent of several North American yellow or red cedars. In overall physical appearance, however, it most closely resembles the giant sequoia of California--a towering stout trunk with a ragged pyramidal canopy on top. To early colonists the resemblance of the alerce to the sequoia was uncanny. The wood lends itself to the same uses as redwood; alerce's soft, decay resistant wood is well suited for boat hulls, shakes, shingles, boardwalks, and hand-carved crafts. The utility of alerce wood and a low reproductive rate have in fact been key liabilities for the species, leading to its rapid decline throughout its natural range.

To really understand how alerce fits into the larger scheme of things one needs to consider a bit of geography. Although South America is an enormous continent, its temperate zone (where near-freezing or subfreezing temperatures commonly occur) is quite small, remote, and isolated from other like climates in the world. It is but a narrow sliver down the slopes of the Andes from central Chile down to the tip of South America at Tierra del Fuego. These forests developed in near-total isolation from the extensive temperate forests of North America, Europe, and Asia. They most likely were at their zenith in what is now Antarctica prior to when the continents drifted apart and moved to their present positions. The southern supercontinent broke apart into small segments quite early, and by virtue of their isolation allowed for the survival and evolution of primitive groups of plants and animals which, if they ever occurred in the Northern Hemisphere, became extinct long ago. Monkey puzzles (an evergreen), for example, are among the most primitive of conifers, but have persisted only in isolated temperate rainforests in the Southern Hemisphere: Chile, Brazil, New Zealand, new Guinea, and Australia. Similarities between trees in the two hemispheres today are most likely to represent basic adaptations to a similar climate rather than genetic ties.

Only two conifers in the Southern Hemisphere are capable of growing into magnificent patriarchs towering over the hardwoods: the kauri of northern New Zealand and the alerce of southern Chile. The kauri (in the monkey puzzle family, Araucariaceae) generally occurs as scattered individuals in mixed forests, with some trees reaching 18 feet in diameter. The trees are often heavily decayed in the center and were exploited for gums and other extractive chemicals found at the base of the tree. They grow only in the northern part of the North Island of New Zealand which is almost subtropical in nature.

The alerce can be a huge tree by any standard. Mature trees growing on good soils and protected from winds can routinely reach twelve feet in diameter. The most magnificent alerce forests cleared by Spanish and German colonists in the early 1800s were reputed to include trees as large as 16 feet in diameter. This ranks with the largest conifers in the northern hemisphere (Sitka spruce, coast redwood 16.4 feet, Douglas fir 14 feet, western red cedar 20 feet). In terms of height the alerce is exceeded by most Pacific Northwest conifers, even though it is one of Chile's tallest trees. The perpetual winds of the region (the forty-degree latitude belt in Chile is often called the "roaring 40s" for its winds) are probably responsible for the relatively short stature of alerce trees--generally about 100-135 feet.

In terms of age the alerce stands alone as a forest tree. Recent studies have documented average-sized trees (3-6 feet in diameter) more than 2,000 years old; the oldest specimens are estimated to exceed 4,000 years. The largest conifers in the Pacific Northwest typically attain only 1,000-1,200 years of age. The oldest giant sequoias and yellow cedars reach only 3,000 years, and many of these are considered overestimates. Even under ideal conditions the alerce usually grows at a snail's pace. Clearly this is a plant that has evolved to tolerate and persist on poor soils and poor growing conditions rather than to outgrow competing species.

The alerce once extended throughout much of the temperate zone in South America. There is much scientific debate over the causes of its decline, including changes in climate (a drying trend) and human influences (fire, clearing, and grazing animals). Like many other cypresses it often does not regenerate well, due to poor quality seed or exacting requirements for germination. Of course for a tree that can live 4,000 years, rapid regeneration may not be all that important for its evolutionary success.

Ecologically, the tree occurs in two distinct kinds of habitats: frequently disturbed high-elevation, well-drained and exposed ridges, and low-to mid-elevation valleys or gentle slopes that are usually poorly drained of water. Most of the low-elevation and easily accessible alerce forests on poor soils have already been cleared, but good examples of mid-elevation valleys and high-elevation forests still remain.

In low-elevation valleys alerce can form pure cathedral groves. These unique forests usually owe their origin to catastrophic events such as landslides or mudslides which eliminated all competing hardwood trees. Even under ideal conditions the alerce is unlikely to grow sufficiently fast to keep up with hardwoods. Its niche is to grow on poor soils which are difficult for other species to grow on. Once a dense canopy is formed the alerce shades out most other competing trees, including its own seedlings.

Reconstructing the history of these forests is often quite revealing. Because of the resistance of alerce wood to decay, logs can be found on the forest floor that are 1,000 or more years old. One can find generation upon generation of hardwood that has germinated, grown, matured, and died beneath an alerce patriarch. These are the forests that some scientists estimate can exceed 4,000 years in age. Within the annual rings laid down by these trees are clues to thousands of years of climatic changes, including storms, droughts, and even glacial advances.

At higher elevations, especially on exposed ridges, the alerce grows in a strikingly different environment. As Darwin observed, the Andes have earned a well-deserved reputation for ruggedness and remoteness:

In vain we tried to gain the summit: the forest was so impenetrable, that no one who has not beheld it, can imagine so entangled a mass of dying and dead trunks. I am sure that often, for more than ten minutes together, our feet never touched the ground, and we were frequently ten or fifteen feet above it, so that the seamen as a joke called out soundings. At other times we crept one after another on our hands and knees, under the rotten trunks. Here we were more like fishes struggling than any other animal.

Alerces grow in these rugged entanglements of hardwoods, especially on exposed ridges, and generally regenerate more frequently and reliably than in the dense groves in more protected environments. With forests under constant attack by snow avalanches, landslides, mudslides, high winds, and the like, alerces have abundant opportunities to establish new seedlings. One can often find a wide assortment of ages and sizes of alerces in this environment. These mixed forests are the most diverse forests in which alerces occur, and are actually the most widespread habitat for alerces. Alerces also occur in mixed hardwood forests at lower elevations, but are usually much rarer, and are less successful at regenerating in disturbed sites there than at high elevations. At its southernmost extreme of range, alerce exist only in unstable and highly disturbed habitats at high elevations.

These remote South American forests represent one of the last remaining examples of pristine landscapes, full of biological richness and intricate interdependent webs. These complex biological linkages need to be understood in great detail before it can even be guessed what the biological consequences to economic development will be in the rapidly changing societies of Chile and Argentina. It is one of the few places where large trees are classified as endangered species and where so many species of both plants and animals are unique to an area. To solve the big issues of balancing the environment with both short- and long-term economic development, ecologists clearly are going to have to use all available evidence to understand how forests relate to the vagaries of climate and soils. Science can no longer afford to continue to ignore the ancient and bizarre forests of the alerce.